Monday, August 11, 2014

Pebble Steel - the best digital watch I could wish for

In the early 80s, I built my first digital clock using exclusively TTL ICs. I had a crystal oscillator driven by 7400 NAND, a cascaded frequency divider using 7493 Binary counters to get the 1Hz clock and 16Hz for time adjust, cascaded counters for the clock itself, and a multiplexed display using 6x7-segment LEDs (VQB71) decoded with 7447. For a 14 year old geek, it was an amazing journey to build it and see that it actually works. Later I changed the LED display indicators to Russian Nixie tubes but had to re-work the whole display part.
Ever since, I was always inclined to wear a digital watch and especially liked the ones with unusual display but never liked their build design. In the 80s and even today all digital watches had / have the typical shiny metal Timex look or the rubberized Cassio look but they always felt very plastic, cheap and unattractive, so I found myself reverting to the classic analog watches because of the huge variety of designs. When it comes to modern digital watches for the average Geek, I must mention TokyoFlash. They have some pretty cool and unusual designs.
There is another problem I had - one looks at the watch a number of times a day, every day, every month and if you are like me - I'd get tired of the same watch after a month or two and would like to see something else on the display but then it means owning and maintaining a bunch of these watches and who has time and money for that.
That's until I discovered the Pebble Steel - IMHO this is the best digital watch hands down. Note that I am not saying it is the best Smart Watch, which probably it is too. But the ability to use thousands of watchfaces is amazing and the simple yet classic stainless steel look is amazing.

 It has a touch of a "retro" with the rectangular face and the geekiness of the Marvin Malton 160 Flying Hour. It might sound like an oxymoron but it has a stylish look for the geeks. The buttons, which actually stick pretty far out are another very nice touch. The thickness and overall size are just  about right for my hand. There are a two types of finishes and two watchband options - I personally prefer the metal band (although the leather band is pretty nice too) and the stainless steel look. I only wished they didn't display the "Pebble" branding so prominently on the face of the watch - it is somewhat distracting. It just needs 2/3 of this font size IMHO.

What is even better, one can easily build a watchface - after releasing SDK 2.0, pebbles brings the programming side more in-line with the conventional C++. Writing code for Pebble requires some getting used to but it is not that complicated and the SDK is well documented! Here is a version of the Text Watch I wrote (reusing an existing conversion routine for numbers to text out of sheer laziness), but this watchface displays the time using Cyrillic alphabet in my native Bulgarian Language. It can be found in the Pebble Appstore as Bul Watch. The words for "eleven" and "twelve" in Bulgarian language are pretty long, so the font size changes to smaller one when the animation will fly in these words and go back to large when any other word is displayed for the hours text.
Even if you don't care about the Smart Watch capability and Smart Phone connectivity - Pebble Steel works fantastic as plain old watch and you can load some pretty awesome watchfaces. The major drawback is the need to charge it every 7 days, but the magnetic charging cable makes it very easy.
"Major" drawback is when compared to a classic digital watch. It is actually a  major advantage compared to other smart watches. No other smart watch on the market has such battery life! I am a guy who works long hours and I need something that will last for days between charges ! I don't want a useless chunk of metal of my wrist by mid-day! So battery life is fantastic for what it does! The display is great too - black and white but perfect under direct sun light!

Thursday, January 23, 2014

The Intelligent Telescope Dew Shield - iDewShield

Dew has always been a problem during telescope observation, especially so in the summer. The front lens of the telescope cools down rapidly due to emission cooling - the telescope points to the clear sky which readily absorbs any emitted heat by the front lens with nothing to reflect the IR radiation back - the deep-space literally sucks out the heat. As a result, the temperature of the lens drops past the dew point and then humidity in the air forms condensate on the glass.
Dew not only spoils the observation sessions but also dissolves contaminants in the air thus causing deterioration of the anti-reflective coatings. No matter how you slice it - it is a bad thing.
Dew Shields help marginally and they are big and clunky - this adds more weight on the mount too. Heater strips work but they need big marine batteries to haul around and you don't want to over-heat the lens assembly or SCT corrector plate/secondary mirror nor you want to be in the need to jump-start your car. After all, the telescope OTA should stay as close as possible to the ambient temperature to avoid internal air turbulence too.
So, here is the idea I have and it is what I have been working on lately - an Intelligent Dew Shield - iDewShield (again, the dreaded Apple Computers naming convention) based on the Arduino Controller.

The idea is rather simple but should be very effective. Relative Humidity and Ambient  Temperature sensors collect air data and the controller calculates the Dew Point. Then a few degrees of difference are added to the dew point temperature in order to makeup for acquisition inaccuracy and to introduce thermal "inertia". An angled Infra-Red Temperature sensor takes sample of the front lens temperature through a hole in the dew shield - no obstruction of the lens and safe way to sample the temperature from a distance. This data is fed to a comparator which controls a Pulse-Width Modulation circuit for the Heater Strip.
The main issue is that the anti-reflective coating and the metal cap in the middle, holding the secondary mirror will have too high reflectivity and low emissivity - this can be resolved either by calibration, factoring the reflective coefficient, or by covering the back of the metal cap of the  secondary mirror holder with black, dull tape.
Knowing the exact Dew Point allows the system to heat just a few degrees above it to prevent condensation.
The main advantage of iDewShiled is that - there is no danger of excessively heating the lens and it will be a tremendous energy-saver when operated on battery. Because the lens temperature will be just what is needed to prevent dew from forming and not more, internal air movement due to convection will be minimized in the OTA. Finally, no modification to the telescope is needed - the iDewShield attached to the front with a Velcro strip just like a regular flexible Dew Shield. Adjusting the distance between the IR sensor opening and the front edge of the OTA allows for a precise "spot" measuring of the lens temperature as the sensor has a tight directional pick-up pattern.

A red LCD display with variable brightness, will allow the user to monitor lens temperature, air temperature, air humidity and calculated dew point. The controller will also include low voltage alarm and a voltage shut-down threshold. Calibration constants for all 3 sensors can be entered using a simple 3-button interface.
I am also toying with the idea to include a "dumb" mode - the ambient temperature sensor will be removable from the main sensor unit and can be inserted under the Heating Strip or attached the lens retaining ring with tape/magnet. In the "dumb" mode the controller will operate just as a regular thermostat following a preset temperature.