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1  Community / Gigs and Collaborations / Re: Paid project - Peltier driver/controller on: March 25, 2014, 04:18:08 pm
Ok, while I was composing a reply, several others posted and you answered some of my questions already.

Are we talking about delivery of a working system, just design and coding services, or something in between ?

To my view, you are looking at one Arduino with a suitable temperature sensor and high current DC PWM output per peltier device with perhaps a RaspberryPi + monitor and keyboard as the central control station.

I am willing to help on this project.  PM me and we can negotiate.
2  Community / Gigs and Collaborations / Re: Paid project - Peltier driver/controller on: March 25, 2014, 02:36:11 pm
 - "+/- 0.2 degrees" is a fairly tight control loop.   in fact, 0.2 degrees is tighter than the limits of error for many sensors.   celsius or fahrenheit ?  are we talking about controlling just the surface temperature of the peltier device, or an airspace surrounding it ?   any thoughts on what sort of device you want for the sensor ?   

 - please elaborate on what you want as far as the LCD display is concerned ....
3  Community / Exhibition / Gallery / Re: Arduino 6502 emulator + BASIC interpreter on: November 02, 2013, 03:45:35 pm
Very cool !
4  Community / Bar Sport / Re: electricity and safety on: March 30, 2013, 06:53:11 pm
"strong emotional event" indeed !
I was twentysomething, and as you both observed, I've never done it again, either.
5  Community / Bar Sport / Re: electricity and safety on: March 30, 2013, 02:43:00 pm
Once, the soldering iron I was using rolled off the bench and I caught it in midair ....
6  Community / Exhibition / Gallery / Re: New Etching Method on: March 30, 2013, 02:30:05 pm
The best thing about this is that it uses common substances found around the house, no need for a shopping trip or special order.

Thanks for the useful information ! 
7  Community / Exhibition / Gallery / Re: Heated water bowl for the backyard wildlife on: March 30, 2013, 02:17:18 pm
Answers to questions above, not necessarily in order ....

 - Not a Peltier device, just a resistance heating element, 7.2 ohms, made from fiberglass and silicone rubber.  The board on the left is an old linear power supply , modified to provide 6.7 volts DC, up to 3 amps.

 - a few data points on power consumption;
   - during bench testing back in January, Arduino + heater drew 1.9 amps at 6.6 volts DC
   - Arduino + heater  + power supply measured yesterday with a P3 Kill-a-watt, 4 watts idle, 12 watts full load .  Version 2 will probably include a data logger.   

Oh, and so far no cats (or anything else) have been electrocuted !
Chewing on the line cord is about the only option for that, the cheap plastic enclosure has held up pretty well overall.

 

8  Community / Exhibition / Gallery / Re: Heated water bowl for the backyard wildlife on: March 26, 2013, 08:07:34 pm
Thanks, everyone, for the kind words !

I thought of an automatic water-feed, but the freezing conditions would require a heated line and that just added too much complication for a project I wanted to deploy quickly.  Definitely in the works for next winter, though.  Same for the motion detector camera.

I have seen squirrels, a cat, and birds drinking in daylight hours ... heard sounds in the night, and seen lots of various tracks (raccoon and skunk for sure, maybe opossum)  when there is fresh snow in the morning.  Lots of takers too, the bowl typically needs refilling 2 or 3 times in 24 hours.
9  Community / Exhibition / Gallery / Heated water bowl for the backyard wildlife on: March 26, 2013, 10:30:36 am
Can't resist posting this.
On successive days I saw a squirrel and a feral cat getting water by licking ice in our backyard.
To provide a source of drinking water for all the assorted wildlife living out there or passing through, I built this heated water bowl.



A thin-film heater that I got as a trade show sample years ago and a TMP 37 temperature sensor are attached to the underside of a small, cheap stainless steel pet food bowl using Kapton tape.



A Duemilanove reads the sensor on A0, controls the 6.7 volts to the heater using an FET driven by D3, really all I changed in Brett Beauregard's excellent PID library sample code was the math to change from TMP 36 to TMP 37.



Water consumption and tracks found in snow indicate that a source of liquid water in midwinter is becoming very popular.
10  Using Arduino / Sensors / Re: X-Ray detector/sensor on: February 03, 2013, 05:06:35 pm
Geiger - Muller tube will detect x-rays.  Many designs for the low-current high voltage power supply can be found online.  Old Soviet G-M tubes can  be gotten at reasonable prices.

PIN photodiodes do not require high voltages but the extremely low current signal output makes them subject to noise pickup unless well shielded.

Scintillation crystal + photomultiplier detectors are the most linear, quite sensitive, and can be very efficient, but are more costly and also require high voltage.

Overall I would recommend the G-M tube approach.
11  Community / Gigs and Collaborations / Re: Looking for help to set up an open source charge controller shield + vt100 emula on: December 31, 2012, 04:21:23 pm
Not sure if this will be helpful in your search for code, but the vt-100 terminal was, itself, an emulation of the ASR-33 Teletype.
12  Topics / Science and Measurement / Re: High side current measurements on: March 16, 2011, 11:16:53 am
Quote
and the Arduino is powered by a separate supply (preferably transformer isolated),

So you would need a power supply that is rated for 4KV isolation. That is way above the normal isolation rating of power supplies, even ones using transformers.

A quick look through a DigiKey catalog that happened to be handy shows that many modern mains transformers made to VDE or other EU standards are rated between 3.75 - 5 kV isolation.
13  Topics / Science and Measurement / Re: High Resolution Thermocouple and Data Log on: March 16, 2011, 12:18:55 am
Quote
you could use the ARef input and analogReference() function to scale the Arduino input to 25 or 30 millivolts full scale

The minimum recommended reference is around 1 volt. Below that Arduino is too noisy to produce reliable results.
 
Note also that any attachment to a real thermocouple must use an "ice-point" reference compensation or else you will never know whether you are measuring the temperature at the thermocouple, or the temperature at the junction point.  That is one of the downsides of using real thermocouples.

Thanks, wasn't sure about the noise floor, thats why I inserted a caveat.

Good point about the ice point, too ... most OEM instrumentation fakes this automagically.
14  Topics / Science and Measurement / Re: High Resolution Thermocouple and Data Log on: March 15, 2011, 11:42:37 pm
A standard type K thermocouple will work well above the temperature range you are talking about.
At 900F the output will only be around 20 millivolts, so you might want to use an operational amplifier to expand this to about 4 volts.  Alternatively, you could use the ARef input and analogReference() function to scale the Arduino input to 25 or 30 millivolts full scale.  Not sure offhand if one way would be better than the other.  10 bits of A/D would give you +/- about 2 degrees resolution, not counting the limits of error of type K.
A bare-bead thermocouple made of fine wire will give the quickest response time.  Might be hard to seal at high pressures.
Since you are working in a combustion environment (oxidizing? reducing?), this can affect your choice of materials .... type N might be preferable for a reactive environment.  Sheathing can improve resistance greatly but at the expense of response time.
www.omega.com has extensive reference materials on temperature measurement which may be useful.


Another thought:  what is the thermal coefficient of resistance of your ignition coil material ?
If it is high enough, you might be able to measure temperature directly by measuring voltage drop at constant current like a standard 4-wire resistance measurement (or current at constant voltage if that is more convenient).
15  Topics / Science and Measurement / Re: High side current measurements on: March 15, 2011, 10:25:00 pm
The real issue with measurements at high voltage is one of isolation.
If your HV supply is constructed without using a chassis or other common ground, and the Arduino is powered by a separate supply (preferably transformer isolated), all that the Arduino will ever see is the voltage drop across the current shunt resistance.  This resistor should be 200 ohms to provide about 4 volts drop at 20 milliamps, so as to use most of the 0 to 5 volt measurement range for the area of interest, with an allowance for overcurrent.

Note for safety purposes that the Arduino analog input pin will be at 2 kv, but only with reference to the other side of the HV supply.  Avoid inadvertently providing a path for current flow.
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