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Old 19-04-2014, 16:01   #46
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Re: Refrigerator Thermostat Replacement

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Originally Posted by Zanshin View Post
I do a lot of Arduino programming (plus now I have the Atmel studio and program the ATMega chips directly once I have the software debugged) and you can do a lot to reduce power consumption, the display is probably going to use more power than the Uno. While somewhat more complicated than necessary you have given me some good ideas - I've got a number of small One-Wire bus thermometers and some LCD displays as well as extra Arduino Micros aboard which aren't doing anything and I might build a display with controller for the fridge and freezer (a simple poti to control the temperature will do).
Have you written the C code for the controlling circuit yet? What sort of time delays do you consider realistic?

p.s. I just checked my specs, an the DS18S20 thermometers only go to -10C, so they aren't good enough for the freezer, unfortunately. But I have been wanting to log my fridge temperatures for a long time and I am going to put together a Micro today with 2 or 3 temperature sensors and logging temperature data every couple of seconds to an attached SD card - thanks for the impetus!
In a moment of extreme stupidity I blew the nano so running a mega for now, pulling 500mA at 5v even bypassing the internal regulator so something badly wrong there, think I need to get back to very bare bones to track down what's going on there.
And maybe having the board spending most of the time asleep might be the way to go? , at the moment I've got it looping with a 2 second delay, for no particular reason.
Re the thermometer chips, I think the - 10C is just for 0.5C accuracy, looks like they actually go down to something like - 55C so might be OK for the freezer.
I'm still quite keen on fitting a few more thermometers around - stuffing box, alternator and exhaust water trap would be nice to know for starters , and with a sd card you could record moths of data at a time.

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Old 20-04-2014, 05:36   #47
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Re: Refrigerator Thermostat Replacement

Conachair - I checked the specifications again yesterday and saw what you already noted, the 0.5C accuracy goes to -10C but the range does go to -55c. I broke out the soldering iron and put an OLED display on my breadboarding ATMEGA board with some DS18S20 thermometers and wrote a simple program to show the current temperature in the freezer; this worked well, although I ran the cable through the top-loading door. I have to see if I can reach the back and run the cable from the fridge to the compressor, since I want to install a small 12V fan to circulate the air in the freezer compartment. In case wiring is impossible, I see that I could use the current thermostat cable for a DS18S20 and then run that to an Arduino, which in turn would run 2 cables to the compressor in order to turn that on and off. The compressor fan output has sufficient power supply left to run the Arduino (perhaps not the big MEGA, but I have a number of Micros waiting to be used).
If you want to minimize power usage you will have to experiment for a while, since that involves shutting the system down and using interrupt timers to wake it up every once in a while. I spent a good week trying to get that working, I was good at getting the Arduino to go to sleep, but then they never woke up! There are some good articles on the WWW on simple methods to reduce consumption by shutting off different (unused) functions on the chip that should be more than sufficient. But 500mV at 5V is an awful lot of draw, you are right that you need to check your board.
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Old 23-04-2014, 06:16   #48
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Re: Refrigerator Thermostat Replacement

Well all seems nice and stable in fridge land, another question..
Auto defrost, from Google that seems to work by heating up the evaporator plate now and then for a short time to melt any ice forming, so why not fit some 12v heating wire or similar and do the same on the boat? After sourcing some sort of cheap heating element it would be just a few lines of code to implement, either timed or from evaporator plate temperature.

Any thoughts?

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Old 23-04-2014, 06:20   #49
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Re: Refrigerator Thermostat Replacement

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But 500mV at 5V is an awful lot of draw, you are right that you need to check your board.
Got that down to about 150mA at 12.6v, much closer to the mega specs. Main culprit was a ethernet /Sd card shield. Plus now using at external regulator bypassing the built in one which was creating a lot of heat. Hopefully it should be possible to get the uno board down quite a bit more.

Good luck with your setup.

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Old 17-05-2014, 13:01   #50
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Re: Refrigerator Thermostat Replacement

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But 500mV at 5V is an awful lot of draw, you are right that you need to check your board.
Quick update if anyone is interested..
Had another hit at this over the past couple of days, bluetooth is great
With an arduino uno r3 powered directly from an eBay voltage buck converter the draw at from 12v is 30mA. That's more like it

Plus with a cheap bluetooth board attached to the arduino I can watch what's going on and change the thermostat on/off temps using a bluetooth serial app on an Android (or probably any) tablet

Code:
 H Help: Press 'S' for settings Press 'L' for live data Press 'T' to display time Press 'V' to increase turn on temp Press 'C' to decrease turn on temp Press 'X' to increase turn off temp Press 'Z' to decrease turn on temp ******************************** S settings: Turn on compressor when temperture reaches 5.00 Turn off compressor when temperture reaches 3.50 ******************************** L Compressor is not running Sensor 01 temperature is: Error getting temperature Sensor 02 temperature is: C: 5.00 Sensor 03 temperature is: C: 3.25 Sensor 04 temperature is: Error getting temperature Sensor 05 temperature is: Error getting temperature Sensor 06 temperature is: Error getting temperature ******************************** V Turn on compressor when temperture reaches 5.10 Turn off compressor when temperture reaches 3.50 ******************************** V Turn on compressor when temperture reaches 5.20 Turn off compressor when temperture reaches 3.50
Sorry if the formatting falls apart, but it's a great way to communicate with the arduino.

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Old 18-05-2014, 07:29   #51
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Re: Refrigerator Thermostat Replacement

Cool stuff. I've been researching Arduino and reading Richard's refrigeration book.

Lots of possibilities for Arduino apps on a boat (...and on my old RENIX controlled Jeep, and beer brewing...). I plan to go full on Geek with Arduino in my off season. Haven't written code in at least 20 years...should be fun. Also could be good application for engine monitoring.

I like the idea of having one for monitoring, control, and education for refrigeration, but think I will keep a good old manual thermostat in place (but not connected) as a back up.
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Old 18-05-2014, 10:19   #52
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Re: Refrigerator Thermostat Replacement

I recently replaced the analog controls on my soda machine with one of my R/C controllers that use a MSP430 processor. These processors can shutdown everything but a timer to wake it up, and draw insignificant amount of electricity. I used a LM34 temp sensor, so used a 5v power supply to power the board and the LM34, and a solid state relay that triggers on just the 3v output from the msp430. Nothing fancy on the controls, read the temp and turn on/off the compressor. I removed the radio part from the board.

And I just replaced my pool timer with another one of my msp430 boards originally built to charge NiMH batteries. I wrote the code to make it a sprinkler timer, but for the pool timer, the 12v output triggers relays to the pumps instead of sprinkler solenoids.

I'd look into the MSP430 processors, TI has starter kits and lots of support.
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Old 20-05-2014, 02:39   #53
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Re: Refrigerator Thermostat Replacement

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Cool stuff. I've been researching Arduino and reading Richard's refrigeration book.

Lots of possibilities for Arduino apps on a boat (...and on my old RENIX controlled Jeep, and beer brewing...). I plan to go full on Geek with Arduino in my off season. Haven't written code in at least 20 years...should be fun. Also could be good application for engine monitoring.

I like the idea of having one for monitoring, control, and education for refrigeration, but think I will keep a good old manual thermostat in place (but not connected) as a back up.
Engine monitoring is the next step, specifically alternator temp, stuffing box temp and exhaust temp for starters.

The ds18b20 sensors are great.. http://www.ebay.co.uk/itm/DS18B20-Wa...-/281196510657
You can wire them in parallel using just 2 wires, each sensor has its own unique address.

Before heading of the beaten track again I will probably have a manual thermostat ready as a backup as well, though,like so often in sailing there just isn't enough data to even make a guess on which is more reliable : some gas in a pipe mechanically switching a load of silicon which runs the fridge, or a little more silicon...

One plus fro the arduino is with a few lines of program I can tell the compressor to not run for 10 minutes while a weatherfax comes in, more than once there's been a soggy fridge or getting to turn it on again in the past

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Old 20-05-2014, 02:42   #54
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Re: Refrigerator Thermostat Replacement

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I'd look into the MSP430 processors, TI has starter kits and lots of support.
Thanks, amazingly low power draw! Makes 30mA look greedy.

Maybe a bit on the low side for memory though.

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Old 07-09-2014, 23:02   #55
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Re: Refrigerator Thermostat Replacement

conachair, I got an arduino and have been having fun with it. One project I want to do is tools for monitoring/diagnostics of fridge. Do you have code/circuit diagrams you are willing to share?
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Old 08-09-2014, 05:20   #56
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Re: Refrigerator Thermostat Replacement

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conachair, I got an arduino and have been having fun with it. One project I want to do is tools for monitoring/diagnostics of fridge. Do you have code/circuit diagrams you are willing to share?
Away from the boat so can't help too much with the sketch, but first thing I would do is get a handful of ds18b20 temp sensors off eBay, they're great, each has it's own address and can be strung in parallel only using a couple of pins. Also something like this.. https://www.adafruit.com/product/1141 will give you a clock and Sd card to log all your lovely data onto. There's a huge amount of help on various forums for writing the software, my sketch is mostly cut and paste from the examples supplied.
Have fun
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Old 08-09-2014, 19:08   #57
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Re: Refrigerator Thermostat Replacement

Cool shield. Sketch should be relatively simple for fridge monitoring/diagnostics, but if you think of it when back on the boat please send it my way as an example.

Currently building a Arduino/Android based system for decoding the old RENIX control system on my Jeep. Moderately complex. Plan to adapt it to an engine monitoring system for the boat.

First code I've written in at least 20 years...fun stuff...reminds me of why I got into tech as a career all those years ago.
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