Diffusion Cloud Chamber (Part 3)

All cable interconnects for this project were salvaged from old PC power supplies. The only exceptions are the Teflon insulated corona-free HV cable (rated at 15kV) and all top-side wires (for heater and light bars) which are silver-plated Teflon insulated stranded wire. All rocker switches are rated for 20A but the only critical circuit in terms of max current is the Power B switch for the 3rd TEC Stage where the current is 18A.

This is the underside of the completed Cloud Chamber. 

Removing residual heat left after the liquid cooling stage helps a bit by lowering the temperature by another 2-3°C. To accomplish this, a system of fans was designed - two small fans blow air horizontally across the fins of the heatsink, while another exhaust fan picks up the hot air on the other side of the heatsink and blows it out in the open thru the back of the enclosure. This system works for the tight space we had to work with. The screws keeping together the Cooling Unit "sandwich" are used to support the brackets for the exhaust fan and the thin plastic air guides using a set of stand-offs.

The intake pair of fans and the blue exhaust fan. Sheets of thin transparent plastic form air channels to contain and direct the stream of air into the fins of the heatsink.
An aluminum L-bracket secures the two stainless steel T- splitter for the coolant - the bottom one on the picture is the inlet for the cold water and the top one is the warm water outlet. The splitters also act as adapters converting the 3/8" ID water supply tubing to 2 x 1/4" ID silicone tubing connected to the copper water cooling blocks.

The front panel's Industrial Digital Thermocouple Thermometer (Lascar DTM-995B) is on the right-hand side. DTM-995B supports T, J and K-type thermocouples, it has a switchable backlighting, °C/°F display units and switchable Current/Min/Max display (a little button, installed next to the display, not seen in the pictures, scrolls through the 3 readings). I installed a Cryogenic-optimized Type T thermocouple and the thermometer was calibrated for this probe before the installation at the Cooling Unit. K-type thermocouple which is more common can also be used but it is not as accurate at low temperatures. There are two adjustments on the back of the thermometer for calibration - Offset to set the 0°C value and Calibration for 100°C

Due to the close proximity between the thermocouple probe cables / thermometer and the HV lines leading to the Discharge switch, additional insulation (Neoprene foam sheet) was added and zip-tied to the HV cables. Any arcing there can destroy the digital thermometer or the power supply.
I took apart an identical switch to the one used for the HV/Discharge circuit and made sure that the distance between the contacts is at least 2 mm in the opposite throw of "Discharge" when the switch is in HV ON position - this should be enough to prevent HV leakage / arcing thru the Discharge circuit inside the switch as Air breakdown Voltage is generally 3kV/mm.
I was toying with the idea of using a HV vacuum relay instead of the switch but it was going to be just over-engineering on my part for only 4kV.

Thin, transparent plastic sheets, salvaged from plastic packaging are used to create a "scoop" for the heatsink exhaust hot air, just above the exhaust fan. This guide directs the hot air coming out of the heatsink fins directly into the blades of the fan. The exhaust scoop is visible on the right, partially covering the 3 switches. The sheet separating the air intake and the air exhaust can be seen on the left/center of the picture and it is secured by the screws on the heatsink.

In this picture, on the right side, one can see the two power resistors (50 Ohm (2 x 100 Ohm /3W in parallel) and switch used to control the power levels to the heater. Heater power is switchable between 1W on LOW (running)  and 1.4W on HIGH (start-up).
The 3 terminal strips are used to distribute different PS voltages to various circuits of the Cloud Chamber - this makes it really easy to change the power configuration of the TEC modules.

Proper tangential lighting above the Active Zone is absolutely essential for good observation of the vapor trails left behind the charged particles. We used 2 opposing light elements - each light bar contains 9 evenly-spaced Super-Bright White LEDs. The LEDs are mounted very low, just above the Active Zone, illuminating the supersaturated alcohol vapors at a steep angle. Standard 5mm LEDs with a built-in lens work best providing sharp bright light beams compared to large diffuse light LEDs.
The 18 LEDs are electrically divided into 6 groups and each group of 3 LEDs in parallel has its own 150 Ohm current limiting resistor. There is a simple Brightness control facilitated by a potentiometer and DPDT light switch with OFF, HIGH and LOW (adjustable) beam settings. LOW brightness includes a 1 kOhm trimmer-potentiometer in the circuit, allowing for a variable brightness level. This can help when doing long exposure still photography or videography of the Active Zone of the Cloud Chamber.
Two PCB strips with width of 1cm are used to form each Light bar. The strips are attached to each other at 90 deg using heavy gauge solid bus wire. The PCB design is fairly simple and can be etched easily at home or the copper can be mechanically removed with a Dremel tool to form the pads and traces.
Visible on the picture is the closed-cell foam "Vapor Fence" intended to contain the supersaturated alcohol vapors above the cold plate so they don't spill over the entire surface of the volume.
Since the vapor trails are whitish, everything inside the Cloud Chamber should be colored black for maximum contrast and visibility of the white trails.
The Active Zone is covered with Black Self-Adhesive Aluminum foil - this type of foil tape is ideal for the purpose as it has a wide temperature range adhesive, it has alcohol-resistant paint and it is heat conductive. This kind of tape is normally used in Broadcast studios by the Lighting Technicians to modify / mask studio spot lights and in comes in 2" width.
Also visible here is the outer Neoprene foam seal for the chamber's cover.
The air inside the chamber must be perfectly still so the vapor trails are not disturbed by air turbulence when formed. This seal prevents any air from coming in or out when the volume cover is in place, eliminating any draft and possible air turbulence.
All seams on the bottom and around the Active Zone are sealed with Black RTV Silicone sealant to prevent alcohol from seeping thru and infiltrating into the Cooling Unit.

This is the finished top side of the Cloud Chamber setup without the volume cover.
The top surface of the chamber's enclosure is covered with a fairly thin (~ 2 mm) black rubber sheet (We picked up this in the flooring section of Home Depot). The rubber sheet was glued using non-foaming Gorilla Glue to the top of the plywood. Gluing this rubber sheet was a bit tricky though - I had to make a jig to clamp and provide even downward pressure on the entire surface while the glue was curing to avoid any wrinkles or air pockets but the result turned out to be excellent.
Aluminum L-shaped profiles are used as a trim for the side edges of the enclosure.
The rubber surface around the chamber's volume provides a nice, durable, non-slippery, alcohol-resistant work area which can be used for additional experimental equipment, specimens, photographic equipment, etc.

The Heater element of the Alcohol Evaporator Unit. The Cloud Chamber relies on a steep temperature differential / gradient between the top part and bottom part of the chamber's volume. Raising the temperature of the top side helps with the alcohol evaporation. We constructed the Heater element from 6 x 68 Ohm (0.25W) resistors organized in two parallel strings - each string has 3 evenly spaced resistors in series. The total resistance of the heater is approximately 100 ohms, dissipating 1.44W at High setting. At Low setting, the heater runs thru an additional 50 Ohm resistance and the heater element dissipates 0.64W.
The heater is powered with 12V from the main power supply. The resistor strings are connected to Teflon insulated wires and placed inside heat-shrink tubing, . A small pair of barrel connectors (M/F) is used for the electrical connection, making the heater replaceable / interchangeable in case we decide to experiment with different heaters / power levels.
The power supply line for the Heater comes thru the top surface, goes into one of the Delrin rods thru a hole on the side and exits from the top opening, terminated by the heater jack.

The completed Alcohol Evaporator Unit. The Heater element is inserted between 4 sheets of black felt squares. The felt squares serve as "alcohol reservoir" and are thoroughly soaked (but not dripping!!!) with Isopropyl Alcohol before the Cloud Chamber is closed and started. Felt material is ideal for releasing the alcohol vapors as it provides a very large surface area and even evaporation. Different number of felt sheets can be used for different run times / amount of alcohol. Heat is absorbed by the top and bottom sheets and alcohol vapors seep thru the mesh supporting them above the Active Zone of the Cloud Chamber. With 2 felt squares the Cloud Chamber can run for about 1.5 hours before it requires removal of the alcohol condensate from the bottom plate. This can be done with a Squeeze-bottle, syringe or just soaked with one of the felt squares and then recycled.

The High-Voltage Positive Supply line comes thru the top surface and connects to the Ion Scrubber mesh on top. The wire is inserted in a black heat-shrink tubing and spliced to a thinner and more flexible Teflon insulated wire, which allows for the metal frame holding the mesh to be adjusted up or down as needed.
While the Cloud Chamber will operate without an Ion Scrubber (IOS), the IOS greatly improves the performance of the Cloud Chamber and IMHO it is a "must-have" feature. 

The electric field cleans the air from dust contaminants when the Chamber is first started and vastly improves the visibility and the definition of the vapor trails by quickly removing (scrubbing) the ions. With IOS turned off, tracks are much thicker, linger for a longer time, less defined and much lower in number. When IOS is turned ON the effect is rather dramatic - the number of visible tracks jumps many times, tracks are very crisp and well defined and the chamber quickly resets itself, clearing old trails.
Total of 4 cables come from the bottom compartment to the top surface - 2 x for the two Light Elements, the High-Voltage IOS supply line and the Heater lines. The rubber top surface provides a very nice and tight seal around each cable as it tries to self-close.

The transparent acrylic Cloud Chamber cover. It is a 6" x 6" x 6" inches (inside) hollow, 5-sided cube and provides enough vertical height for a good temperature gradient and excellent viewing angles. We picked up the acrylic cover on eBay, sold as Trophy / Memorabilia cover and it works for the purpose as a temporary solution during testing but it will be replaced with a custom-made glass cover.

This cover contains and seals the volume of the chamber and it is best if it is made out of glass - we are planning on using 3/16" glass when the cover is replaced (just the standard "fish-tank" type construction and silicone adhesive). Acrylic plastic doesn't react well to saturated alcohol vapors and low temperature - eventually it becomes brittle, cracks and flakes.
 I designed a special "Neoprene" foam seal for the bottom edge of the volume cover. This seal is air-tight and completely seals off the volume of the Chamber when the cover is inserted. It is made of 2 different thicknesses Closed-Cell Rubber Foam material - the thin, bottom layer seals the under-edge of the cover - it has an inside lip on which the cover "steps on", while the thicker outside foam rim seals the cover on the outside wall. The seal is glued with black RTV Silicone to the top surface and provides also mechanical stability of the cover as it is a tight-fit and locks-in the cover in place.

Update: Finally, I built a proper volume cover to replace the acrylic one . It is made of 3/16" thickness glass with an inside dimensions of 6" x 6" x 6". The glass sides are glued together with clear RTV silicone sealant (just as if you are building a box or a fish tank)  and then the edges were reinforced and protected by gluing over each of the edges an aluminum angle (L-profile) 1/2" x 1/2" x 1/16".
The top edge trim was made of the same material in sections of 6" with 1/2" cutout on one of the sides to cover each corner's top side.

I built the cover in 3 steps - first is to glue the glass, after the silicone completely cured, I removed all the excess from the seams (inside and outside) and then glued with the same sealant, the corner aluminum L-trim. Working with silicone gets very messy and you have only a limited time before it starts setting so doing it in 3 steps affords more control over the build process (but the cleanup stage can be time-consuming and I recommend using masking tape to minimize cleanup).

The bottom 1/2" glass of the side edges was left without the protective trim in order to ensure a tight side seal when the cover is inserted into the custom gasket.

The bottom edges were trued by polishing the cube edge over a very flat, machined surface with sandpaper until the edges became smooth and straight on the bottom for a really good seal.

Diffusion Cloud Chamber (Part 2)

After the cooling element was constructed and installed we did a quick test run to prove the concept and to make sure that we can achieve our goal of -36°C.

Unfortunately, the IR thermometer I had at hand was not at all accurate at very low temperatures! I had a black matte finish aluminum tape over the copper plate for this measurement to reduce the reflectivity and improve the emissivity of IR radiation and it still showed about 10°C error. The actual temperature, established later with a proper calibrated Type T thermocouple was -37°C - still exceeding our design goal.

Wiring of the front panel. We used the rest of the 2RU aluminum blank for the front panel. All Cloud Chamber control switches, indicator LEDs and the cold plate thermometer were mounted on the front panel. The back side was left open for the water feedlines, power connectors and air cooling.

The Cloud Chamber is powered with two individual Power Supplies.
The main Power Supply is a 450W PC ATX power supply. This type of power supply serves the purpose well as it provides enough power and variety of voltages for all of the circuits - the heater element of the evaporator (+12V), Ion Scrubber HV supply (+3.3V), Light bars (+5V), Front Panel Thermometer (+5V), First stage TEC (+3.3V), Second Stage TEC (+6V per element - actually 12V/2 as they are wired in series) and 5th Stage cooling fans (+12V). Same power supply also powers the Liquid Cooling Plant (+12V and +5V).
The ATX power supply plugs in directly, in the female connector of the main wire harness and it is switched on/off by the main power switch on the front panel.
The second power supply (Power B) is 15V/32A (Alinco DM-330MVT) and it is exclusively dedicated to Stage 3 TECs as they require the most power. The voltage in Stage 3 should never exceed 15V! (maximum rated voltage for TEC1-12709 module is 15.1V). All wiring for Stage 3 is done 12AWG stranded wire due to the high current demand of  the dual TEC1-12709 modules.

To facilitate the wiring of multiple circuits, three 5-position terminal blocks were mounted. One of the blocks is all GND terminals while another other block is dedicated to the TEC modules and the third block is used for all other circuits - HV PS, Lights, Heater element, etc. The ATX PS main wire harness was connected on one side of the terminal blocks. We used PC PSU Extender Cable for the main power harness - one side of the extender cable comes with a female ATX connector - the male connector on the other end of the cable is simply removed and all wires are terminated with spade terminals.

The top side of the Cloud Chamber under construction.

Visible is the Cooling Unit, attached with countersunk brass screws to the plywood. 4 x Black Delrin 5" x 1/2" rods are attached with stainless steel machine screws (1/4"-20 x 1") to create the "support pillars" for the Positive mesh of the High-Voltage Ion Scrubber and the Alcohol Evaporator Unit / Heater sitting on top.
Delrin (Polyacetal) is a good choice as it is resistant to the hostile environment of super-cold supersaturated alcohol vapors and it is easy to work with. Other possible choices are Ceramic or Teflon. Plexiglass/Acrylic will become brittle under these conditions so I don't recommend using such material (The Chamber's acrylic dust cover which we used during testing while constructing the actual glass cover, for example, started peeling and cracking after a few runs).
The Delrin rods I found were solid so I had to drill and tap all rods on both sides for 1/4-20 thread. One rod was drilled end-to-end to act as a conduit for the heater wires. I drilled a small hole on the side about 3/4" from one of the ends. This hole was drilled at 45 degrees to make the internal cable routing easier to deal with.
The rods are placed very close to the inside wall and corners of the Cloud Chamber Cover (outlined with pencil marks on the top surface in this picture) while making sure there is enough clearance to slide the cover on freely.

The fine aluminum mesh of the Positive terminal of the Ion Scrubber is stretched over a brass tube frame, using a very thin silver-plated wire. The frame is constructed out of 4 brass tubes, slightly larger in diameter than solid 12AWG wire. Each corner of the frame is a solid copper 12AWG wire loop formed in a loop around the Delrin rods with ends at 90 degrees. The ends of the loop are inserted in the brass tube segments and then soldered. This arrangement is allowing the frame / mesh to be moved up or down, sliding over the corner posts.

We wanted to be able to adjust the height of the mesh in order to control the intensity of the electric field above the Active zone. A number of rubber O-rings were placed over the Delrin rods below and above the corner loops of Ion Scrubber mesh to act as "movable stoppers" suspending the mesh at an adjustable height.
Another brass frame made of flat brass stock supports the tin-plated steel mesh (not installed yet in this picture) of the Alcohol Evaporator Unit (AEU). This frame is fixed on the very top of the Delrin rods. Each corner is a copper washer to which we soldered the brass frame elements and the frame is then secured on top of the support pillars with stainless steel screws. The AEU support steel mesh is soldered on the bottom of this brass frame.

This is the completed support structure with the Ion Scrubber HV mesh, the Alcohol Evaporator Unit (the heater element is visible on the very top). The black and green O-ring stoppers and another green O-ring which acts as an "insulator rib" to lengthen the electrical distance between the high-voltage mesh and the Alcohol Evaporator.
(!) Since the Cloud Chamber is filled with a mixture of air and alcohol vapors during operation, an extra effort was made to prevent even a remote possibility of arcing! The temperature in the top portion of the volume where the HV mesh is located is above the alcohol's flash-point temperature. Last thing one wants is a fireball! 

The HV operates at 4.6kV and the Air breakdown voltage is 3kV/mm, so a minimum of 3 mm distance (~2x the breakdown distance) to GND is absolutely mandatory! Any High-Voltage Arcing inside the Cloud Chamber can ignite the alcohol vapors and can also destroy the main Power Supply. This is one of the reason why the heater supply wires were conducted on the inside of the Delrin tube and not just wrapped around it when passing the HV mesh.

The almost finished control panel with all SPST (Power and Power B) switches, DPDT switches, LED indicators and the Industrial Grade Thermocouple Thermometer for the Cold Plate. A quick test showed a good temperature drop. The digital thermometer's display mode selector button was installed later in the build process.

Visible, on the right-hand side is the High-Voltage Ion Scrubber power supply. This was taken out of an Electric Fly Swatter /Zapper. The circuit is made of a DC pulse converter, high-voltage step-up transformer and a voltage multiplier. At 3.3V input voltage I measured output of 4.6 kV.
CERN's recommendation for the Ion scrubber is minimum of 100 V/cm and 4.6 kV is more than enough to satisfy this.
The HV supply is housed in a poly-carbonate plastic box (from CCI .22 Cal Ammunition) to provide additional insulation and safety. A special, high-voltage, Teflon insulated, corona-free wire (rated at 15kV) is used to connect the positive output to the top-side mesh. The negative pole is connected to both, the aluminum plate and to the copper cold plate of the cooling element.
The HV supply has a capacitor on the output and since this is a school project, I would imagine that no kid would like to be zapped by 4.6kV. I designed a dedicated Discharge circuit to prevent any unpleasant accidents. Half (one pole) of the Ion Scrubber DPDT switch is used to control power to the HV PS. The other pole of the same switch on the opposite throw is used for discharge. 

When the HV PS switch is flipped to DISCHARGE position, the other pole of the switch shorts the HV output thru a 15 kOhm / 3W metal-oxide resistor to the negative side. The middle position of the switch is OFF, the UP position turns power ON to the HV PS and the DOWN position is DISCHARGE - it basically shorts the HV output capacitor (In this position, the LV power to the HV PS is already disconnected).
The safety procedure requires the Cloud Chamber to be opened and manipulated only with the switch in Discharge position. 

This circuit can be avoided if enough time is afforded after HV is switched off, before the Chamber is opened, for the voltage to drop down due to HV capacitor's and wire leakage - I measured this to be approx. 30 sec. Using a Discharge circuit just takes the guessing out and guarantees that the mesh is at 0V as soon as the switched is flipped to discharge.

Diffusion Cloud Chamber (Part 1)

One day in February, my son came from school, holding a Science Fair application and said "I am not doing the stupid "baking soda and vinegar volcano" that everyone at school seems to like! I want to do an actual science project!".
Lately, my son has taken a great interest in the model of the Atom, subatomic particles and Nuclear Physics in general, so we knew exactly which direction to go, and we started to brainstorm a possible project. A "Geiger Counter" was what immediately came to mind, but it is a simple straightforward device - quick and easy to build. Then I said - let's take it a step further - why just count charged particles when we can almost see them. Enters - The Cloud Chamber Particle Detector!
There are two main types of Cloud Chambers - The Wilson Cloud Chamber, which relies on a rapid volume expansion to drop the pressure and achieve a vapor supersaturated state and it is only sensitive for a moment and the Diffusion Cloud Chamber (DCC) which relies on super-cooling alcohol vapors to get them to a supersaturated state. DCC is more complex than the Wilson Chamber, but it is continuously sensitive so no danger of missing an event while you are blinking! We decided to go "Diffusion". Such detector requires a plate cooled to a very low temperature. Here is how it works.
A Dry Ice or Liquid Nitrogen (LN) cooled DCC was right out - we wanted to use it at will, without depending on a Dry Ice / LN source, plus storage for these materials is always a problem and you have a narrow window to use the chamber.
Phase-change cooling requires huge, noisy refrigeration units and is pretty complex and difficult to build at home, so this type was also out of our list of considerations!
We decided on Thermo-Electric Cooling (TEC) (also known as the "Peltier effect") - it is not really efficient method, requires a lot of power but it is small and easy to build.
The other design parameter to establish was the size - with Cloud Chambers bigger is always better and more spectacular, just like with a Telescope but using the inefficient TEC means that a large area DCC will be extremely power hungry, with huge power supplies and a lot of supporting equipment. Again, just like a Telescope - too big and you'll use it less often. We wanted something really portable, desktop sized that we can quickly setup, get ready and start experimenting with.

All materials for this project were sourced from eBay, Home Depot and my own electronics junk box.

The most common size "Peltier" cooler is 40mm x 40mm thus two side-by-side units will give us a cooling area of 40mm x 80mm. The final design has a slightly larger copper cold plate of 2" x 4" - not really big but enough to observe well the particle effects and with a fairly small footprint at the same time. The final chamber volume is 6" x 6" x 6" with an Active Zone of 8 sq. in.
Diffusion Cloud Chambers requires a maximum temperature of -26°C (this is the temperature at which alcohol vapor supersaturation occurs) and this means that the Active Zone should be cooled down to at least -35°C from the +25°C room temperature to work reliably - a ΔT of 60°C. To achieve this, a cascaded (multi-stage) cooling will be needed. Cascaded TEC modules are not very good at pumping a lot of thermal energy, but they achieve the highest temperature differential, impossible to achieve with a single stage. The specification for TEC1-12706 shows ΔT of 70°C but this is more of a theoretical value than what my real-world tests showed.
Our chamber has 5-stage cooling - 3 cascaded TEC stages, 1 stage liquid cooling and 1 stage air cooling (both for the main heat-exchanger and also for removing the residual heat of the TEC modules right after the water-cooling stage). Having 3 TEC stages opens the platform to experimentation with different power levels to achieve best optimization and the lowest possible temperature.


2 cooling stacks, placed in a side-by-side configuration. Each stack has 3 TEC modules and a water-cooling block. The stacks are cooling a Tellurium Copper (Alloy C145000) Plate (2" x 4" x 0.25")
The top side of the Cooling Unit is an aluminum plate (3" 1/2 x 5" 1/2) with a rectangular "window" cutout, slightly smaller (3" 7/8 x 1" 7/8) than the cold plate to ensure a slight overlap (1/16") on each side, while exposing most of the copper plate. This top aluminum plate was made out of a 2RU equipment rack blank (the gray plate under the stacks on the picture)


The top surface of the enclosure was made of a plywood square 14" x 14" x 1/2" (in a retrospective, we could have gone 13" x 13" or even a tad smaller) with two sides of pine planks (14" x 3 1/2" x 3/4") attached with glue and long deck screws. In the center of the plywood square, we made another rectangular "window" (approx. 4" x 3" 3/8), this time slightly smaller than the aluminum top plate's narrow side but larger than the copper cold plate. The aluminum plate was centered over the window and attached with countersunk brass screws to the top plywood surface. The copper cold plate was placed over the window of the aluminum plate and centered using closed-cell rubber foam "Neoprene" insulation spacers.
Brass screws were used to mount the aluminum plate (frame) so I can easily solder to one of the screws protruding on the back side and establish an electrical connection between the aluminum plate and the negative terminal of the HV PS.

The cascaded TEC stacks were formed using 2 types of Peltier modules - lower power TEC1-12706 for Stage 1 and 2 and higher power TEC1-12709 for Stage 3.  All modules are in cold side-hot side/cold-hot/cold-hot sequence. The idea is that the first 2 stages are lower power modules and operated at lower than nominal voltage - stage 1 runs at 3.3V and Stage 2 at 6V. The heavy lifting is done by stage 3 (TEC1-12709 @15V). Each stage needs to pump out the heat, pumped by the previous stages AND the heat generated by that stage as well. Running the first 2 stages at lower power prevents stage 3 from being overwhelmed beyond cooling capabilities. In our setup, stage 3 is powered by a separate power supply due to the high current requirements - 15V / 18A or 270W electric power (9A for each stage 3 module in 2 stacks).

In this arrangement, Stage 1 adds ~6W (2 x 3W) of thermal energy which needs to be removed in addition with the thermal energy pumped out from the Cold Plate, Stage 2 adds another ~22W (2 x 11W) for a total of 28W. These extra 28W heat must be removed by stage 3 in addition to all of the thermal energy pumped out from the Cold Plate.
The water-cooling blocks and heatsink must remove almost ~298W of thermal energy burden, generated by the TEC modules in addition to the heat removed from the Cloud Chamber volume.
Cascading the TEC modules also allows for a more gradual heat distribution across the whole stack and brings stage 3 in an area of better efficiency.

All modules are stacked together with generous amount of aluminum-based thermal compound on both sides in a thin and even layer. Stage 3 modules are mounted using silver-based thermal compound on both sides. The two stacks of 3 TEC modules are placed side-by-side along with the water cooling blocks on the last hot side. This whole assembly is "sandwiched" between the aluminum plate/frame (and copper cold plate) and a large copper heatsink. The heatsink is intended to dissipate any residual heat, not completely removed by the liquid cooling stage. The copper water cooling blocks are not 100% efficient (I suspect the internal surface area of the block was not much enhanced) so additional help by the heatsink improves the overall heat-removal process. Copper components were used exclusively due to their outstanding thermal conductivity.

The cascaded TEC stacks are surrounded by tightly fit Closed-Cell Rubber Foam insulation ("Neoprene"). We made 2 foam insulation "frames" (glued together) with a 40mm x 80mm cutout and notches for the lead wires. The top portion of the foam frame fills up the cutout cavity in the plywood under the aluminum plate.
It is important not only to insulate the bottom of the aluminum-copper plate assembly and the TEC modules but also to prevent any heat, rising from the liquid cooling blocks & heatsink and heating up the cold plate so any air convection should be prevented.
1/4" ID silicone tubing is connected to the water-cooling blocks. Both cooling blocks run in parallel using stainless steel T-splitters. Silicone tubing is optimal for this stage as it seals nicely around the barb fittings without the need for additional hose clamps.

The Cooling Unit "sandwich" is held together with small diameter, countersunk, oxide plated, stainless steel screws to minimize heat transfer between the hot and cold sides. These screws must have minimal thermal conductance and their length to diameter ratio and material help a lot, but are also exposed to airflow around the hot side to further cool. The screws go through the aluminum plate and the copper heatsink (3" 5/8 x 3" 5/8 x 1" 1/16) essentially "squeezing" in-between the two plates the rest of the cooling stack - the cold plate, all 6 TEC modules and the 2 water cooling blocks. A dab of RTV sealant was used to seal the wire exit openings in the surrounding foam insulation.

This is the final design of the Cooling Unit for the Cloud Chamber.

Two small holes were drilled in the side of the cold plate - one hole was used to attach screw with wire lug and wire to the Negative terminal of the High Voltage Ion Scrubber and the other hole was filled with thermal compound and accommodated a T-Type (Cryogenic-Optimized) thermocouple probe. A small brass bracket lined with fiberglass tape was used to fix (pinch) the thermocouple probe cable to the plywood enclosure and prevent it from pulling out of the cavity in the copper plate.

When Lightning Strkes ...

This summer was sort of OK for me in terms of Thunderstorm activity in my area except for one particular storm ... I don't remember exactly when it was  - sometime in May or June. There were some frequent lightning strikes in the area and one particular hit was very close to my house. It wasn't a direct hit - I would say it was about a few hundred yards away from the house. We lost power briefly and when it came back - my home network was gone.
Upon a close inspection, the first casualty was a 10-port Linksys ethernet switch - there was charring and obvious damage to the components, with chips blown into pieces, Then, I discovered 2 graphics cards were also gone - a Nvidia GeForce 8800 Ultra on the FlightSim machine and the graphics card on the Ham Shack computer - a Quadro4 NVS280. Finally, the built-in network adapter on the HamShack HP machine was also dead, alongside of a dead USB to RS-232 converter connected to the SteppIR Fluidmotion controller.
I started wondering how the lightning discharge came into the house? ...everything in my lab is grounded - I have a huge copper ground bus, attached with an 8 inch wide solid copper strap to the ground rods and every single piece of equipment in the Ham shack is attached to this bus with  solid copper straps.
For sure it wasn't thru the power lines - otherwise I would have had a lot more damage. It wasn't thru the cable either - TVs, Cable boxes and Cable Modem were all good. All antenna coaxial feed lines were disconnected at the time of the storm so - no damaged radios.
It was a mystery until last week when I powered up my SteppIR controller (it was disconnected from the power supply)  just to be greeted by a dead display and all control LEDs lit up.

This is what the Fluidmotion controller looks on the inside. The thing is a total toss. It absorbed a lot of energy. A lot of the "soot" on the PCBs is in actuality re-deposited metal vapors from the vaporized PCB traces. Even the metallized plastic shell of the male DB-25 control cable connector had some of the metallization vaporized and deposited on the outside of the box.

The controller was grounded via the ground post on the back of the chassis to the main ground bus.

 The transceiver interface board  (top-left) was not spared by the lightning strike - one of the chips was blown to pieces.

It is now obvious that the hit came in thru the control cable. (Continuity checks show both stepper motors - EHU and 80m coil to be OK but I need to test them with a functioning controller.)
 My guess is that the ground wave of lightning strike energy bridged the insulation of the control cable lying on the ground near the antenna. The cable is shielded so it traveled down the shielding of the cable and it found path to the ground via the controller.
Since the controller was connected to the computer, some of the energy traveled thru the serial cable, killing the RS232-to-USB adapter on its path, and down the network CAT5 cable to the switch, killing the switch and the second graphics card in the Flight Sim computer.
The severe damage seen in the photos is due to the poor (other adjectives come to my mind) design of the controller (Thank you for this SteppIR :-( - the outer shield of the female DB-25 connector is not directly connected to the ground lug!!! Instead, the chassis is connected to the board via 2 small posts, supporting the front PCBs. The top cover is all powder-coated, therefore insulated  so no direct path is established from the the DB-25 shell studs to the ground post either. The lightning just traveled thru the main PCB, then thru the connectors to the front PCBs to get to the chassis and ground lug!
This sort of design and execution is rather moronic (and I am being gentle here). Come on SteppIR! If you are in the antenna business, make sure the equipment is properly designed and grounded. Powder-coating and tiny PCB traces are not really "low resistance" for lightning energy - and this was not even a direct hit!!!
They sell a $270 relay option  as a "lightning protection" for the SDA100 (which would be a total waste of money if the new SDA100 controller is grounded internally the same way!)

UPDATE: I just received the SDA100 controller. Honestly, I have mixed feelings about it - while there are a few improvements, I really liked the "one button band selection" mode of the old controller. The user interface remains rather poor and definitely nowhere near the excellent Ultrabeam controller UI. The grounding is improved - they didn't powder-coat the inside on the back wall, thus allowing a direct path between the ground post and the shield of the DB-25 connector.
A couple of tips: The ALP driver board, as I thought is pretty useless - just a bunch of relays disconnecting the driver chips. This will protect the chips from static and over-current but that's about it. At $4.87 per L6219 driver chip (DigiKey) - I need to destroy both of my driver chips 20+ times in order to make it worth the money. I didn't get the ALP driver board and would not recommend it to anyone. The controller is shipped with 4 chips installed, while my BigIR requires only 2 - EHU and 80m Coil so I have 2 spares inside already (the chips are on sockets this time around).
Tip 2: If you really want the ALP driver board and you are buying a new antenna, or controller, don't buy it with the ALP board from the get go - get first the standard board and then later buy the ALP driver board - this way for only $64 more (the difference between the new option price and the upgrade price) you are getting another driver board to have as a spare part.
In this regard, I don't think it is fairly priced - 8 relays and a few more components for $185??!?
Final thoughts after 6 years  - if I had to do my BigIR Vertical all-over. i'd go with the Ultrabeam vertical for sure - the SteppIR design is just executed too half-baked and sloppy for my taste.

StarGate SG-1 Advanced Arduino Neopixel Clock

Update 2020: Code is finally finished. This project was put on back burner for years but now with the Stay-at-home Covid-19 thing, I finally had the time to complete it. The TSL2561 has been discontinued by Adafruit but it is still available from other sources. Hopefully I'll get around to order the current TSL 2591 but this module is using different code - shouldn't be difficult to integrate. Program memory has less than 300 bytes left but I can always sacrifice one of the rtttl alarm songs to free-up some more.

If someone wants to build the clock and beta test it, please contact me and I'll send you a compiled hex file. Ill open the source and release it on GitHub once I am 100% satisfied that there are no existing bugs / issues.

Parts needed for this project: Arduino Uno R3 board, 60 NeoPixel ring (4 x 1/4 arcs), ChronoDot 2.1, TSL2561 light sensor board (I2C), 3 buttons, piezo buzzer and a 270 resistor. (most parts are available from Adafruit Industries). Bredboard and jumper wires for testing are helpful.

My fascination with clocks and watches always has been pretty hard to control.

Of course, when I saw the Adafruit Neopixel 60 LED Circle this was the first and most logical thing to come through anyone's mind. I wanted to check out what other have done with the Neopixel and found the  "Stargate LED Clock" project by David Hopkins (hopo28) on GitHub. It is a really well done clock and has some very cool visual effects. The enclosure is fantastic too - exactly as the clock is named - a Stargate. While David's clock is great, I felt that it lacked some features - it is just too uncomplicated for my taste. The ATMega chip has plenty of performance overhead and more than enough memory so I decided the load the clock with as many features as I could come up with and fit in the 32K flash memory.
I started with David's code as a foundation, made a list of enhancements and started implementing the features one by one. In the process I updated the hardware configuration as well. The clock now uses ChronoDot V2.1 as RTC and Adafruit TSL2561 Digital Light Sensor. To add audio output I added a simple piezzo speaker driven with PWM. To implement a menu system and keep it simple enough to control with only 3 buttons I need to use double-click and long-press button actions. The entire de-bounce routine was replaced.
Just to list a few of the features I have added : Menu System for setting all parameters (including the RTC calendar), using color patterns feedback and only 3 buttons, Advanced Brightness Control system, 6 programmable alarm modes, SunRise Alarm, triggered by the level of the ambient light in the room, Audio Volume control with 10 levels and adjustable "Quiet Hours" mode, Westminster Quarterly Chimes and hourly beeps, 12 Alarm Songs, Full Calendar display - MM/DD/YY, Custom User-Programmable Color Set (stored in the EEPROM, requires an USB computer connection).
My development platform is an Arduino Uno board but I'll migrate the clock to one of the smaller boards.
David has done  a really good job putting together the base of the clock (Thanks so much!) and it was easy for me to understand his functions and  add all these features, even when I needed to re-organize the program flow.

 Just completed the final revision  of SG-1 V2 (I had to optimize a lot of things and move some stuff to PROGMEM - as expected first I ran out of RAM and then out of program memory (blame is on the 12 alarm songs).

Update: I noticed that the Arduino 1.8.12 IDE generates much smaller code footprint and this allowed me to add many other improvements and optimizations. I improved the menu system and also added Time Adjust mode and direct calendar setup.

The development platform / prototype: Arduino Uno board, Neopixel 60 LED Circle, ChronoDot v2.1, TSL2561 Digital Light sensor, 3 buttons, piezzo speaker and a resistor.

The Main Color Set - Time is 11:14am (22 sec)

Main Color Set - Time is 1:19pm (37 sec). The Hour color changes to indicate PM.

Custom Color Set - The color of  each element of the display can be configured independently with a serial console and a text menu, displayed by the firmware. This Color Set has 2 modes and can be configured as either Dark (display off) or Custom Colors (User-defined). 

All colors and clock parameters, including alarm times, modes, sun Rise trigger level, etc are saved in the EEPROM. ChronoDot has its own backup lithium battery so a complete power failure will not affect the clock.

Simple Mode - Hour, Minute and Second  - Time is 11:14am (33 sec)

 Calendar Mode : Date is May (orange) 1st (blue), 2015 (white) Friday (green). The day of the week color changes to red for the weekends. The inner part of clock's face helps to quickly determine the date. The hour dots are used for the month, and the date and year are displayed only in-between the dots. It is a bit awkward at first because of the 4 day increments per segment, but one can quickly get used to it. Only the next 32 years are displayed in two runs - each is 16 years, then a new clock face is needed to reflect the next 16 year segment.

 Alarm OFF (left) and Alarm (ON). Alarm for Week days only. Alarm time 7:00am.

One of the color sets displays the Alarm time and mode. If a dual mode is selected - for instance Alarm on Weekdays and Weekends. the display will alternate between the two alarm times every 10 sec.

Alarm ON on Weekdays and Weekends. Alarm Time for the Weekends is 9:55pm (a favorite TV show starts :-). Hour, Minutes and Modes are all set with  the 3 buttons.

Sun Rise Alarm Modes - triggered only once a day! It can be triggered between 4am and 9am and the actual trigger is the level of ambient light in the room when the Sun raises. The trigger level is sampled beforehand, using a menu item and it is stored in the EEPROM. 

Some  of the configurable Alarm modes left-to-right: Weekdays Time Alarm + SunRise Alarm on the Weekends, Weekends only SunRise Alarm (no weekdays alarm), Every Day SunRise Alarm

Display Brightness Selector - 59 adjustable levels (left) and Auto mode (right) when the display brightness is controlled by the Ambient Room Light Level. The brighter is in the room, the brighter the clock display will be.

Volume Control (goes to 10 only, not 11:-). Left - Hourly Chime - plays Westminster quarter chimes + Bells for each hour, Right - Hourly Beep mode - beeps on the top of each hour. This selector sets also the volume for the button clicks in menu mode. A special Night Mode (Quiet Hours) can be selected - it disables any chimes during the night time quiet hours (Default is 23:00 to 05:00 but it can be changed and saved by the Text Terminal Menu)

Calendar Set Mode. All functions, modes, times and calendar can be set using 3 buttons and the menu system (using single, double-clicks and long-press actions)

There are a functions which require computer - for example to set the Custom Colors and Mode for the Custom Color Set but everything is saved then in the EEPROM.

Part of the menu system - Yes / No selector for Calendar Setup. 

Yes / No selector for Sampling Ambient Light Level trigger threshold for the SunRise Alarm

 Every hour the clock does a random Star Gate visual effect - I didn't change anything in this part of the code - its all hopo28. The effects and animations are pretty cool!
The alarm song selection is a rather geeky (Star Wars, Indiana Jones Theme, etc), but the clock has a RTTTL Player routine so any Rtttl formated song from the web can be added - the only limit is the available PROGMEM space - currently a little over 256 bytes are left from the 32K.

The Text Menu was enhanced a bit to allow setting of the additional parameters and to provide more detailed status. I also added a separate color element for 3/6/9/12 hour dots.

Now I am working on the enclosure - thinking of something like a picture frame, but will explore other options as well. The clock face needs some improvements as well.
Toying with the idea to use the Light Sensor as sort of  a "Shift register" for the Menu. The user can simply cover with one finger the light sensor and this will change the meaning of the button functions - for instance advancing minutes with one button and when the light sensor is dark (covered), the same button decrements the minutes instead. Another feature I would like to add is an automatic DST but I doubt that ill be able to free up enough program memory for this.

Canon EF-S vs. EF Lens shaprness when shooting with APS-C

Since Canon EF-S (S for Small image circle) are the main lenses used with APS-C format cameras, I was wondering what is their quality. There are no L lenses in the EF-S format and I wanted to put them against a similar, kit-grade lens.. I did very simple and un-scientific test and compared 3 lenses - Canon EF-S 18-55mm 3.5-5.6 IS STM, Canon EF-S 55-250mm 4-5.6 IS STM and Canon EF (Full Frame) 28-105 3.5-4.5 USM. These are very inexpensive lenses - both EF-S lenses are often sold as part of the Canon DSLR kits and the Canon EF 28-105mm which was an average (not too shabby but nothing spectacular) lens from the 35mm film days - the one I used was the "better" mark II version (f/1:3.5-4.5, 7 blade, made in Japan). It was a good. well built all-around lens and and a step up from"kit grade" econo zoom lenses at the time (as the EF 35-80mm - a really cheap lens).
All shots were taken with Canon EOS 70D set on manual mode, ISO 500, fully open aperture. The idea was to compare the details in the image thus the lens sharpness. All images are a 100% crop - 1200 x 1000 px  from the original pictures. I chose a subject with a lot of dust particles and imperfections rendering small details.

 EF-S 18-55mm @ 55 mm

 EF 28-105mm @55 mm

EF-S 55-250mm @55mm

Now, this comparison is not quite fair as both EF-S lenes were tested at their very limits where performance is not usually very hot. Still the 28-105mm is the worst of them all even almost in the middle of the zoom range.

Canon EF-S 18-55mm @ ~26mm

Canon EF 28-105mm @28mm

By far - the worst case!

Canon EF 28-105 in "Macro" mode @105mm as close as it will focus.

Canon EF-S 55-250mm did not have such close focus range so I brought the zoom to 166mm to get similar framing, Again it did outperform the EF 28-105mm

So as it turns out - the lenses, bundled nowadays with the Canon DSLR kits are of a much better quality then what you'll get in yester years and will outperform what was considered "an average" lens 15 years ago.