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Old 11-25-13, 03:31 PM   #26
NiHaoMike
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I'm working on the control software. At this point, I can "run" it by manually adjusting the water pump and fan speeds, good enough to prove that it works but not very practical. Can't get any real performance data (apart from that it draws only 300W or so with the fans maxed out and the suction pressure very high for a ES22a/R433b system) without the tank sensors and in any case, I would have to wait until next year to get meaningful results.

There's a dsPIC for the low level control and an OpenWRT (embedded Linux) platform doing the web UI stuff. There's a whole lot to learn. I'm much more familiar with hardware than software.

The interlink between the processors is a high speed UART link. I originally planned to use SPI, then realized it was already used by the SD card... The in-band framing is a little more difficult to program for, but I have learned a little about how to do it. (Reserve two values - a frame delimiter and an escape code, then XOR conflicting data bytes and denote that with the escape code.) The link can run up to 460kbaud (with a very clean signal according to my scope) so even realtime streaming of the voltage and current measurements (i.e. to detect compressor speed with FFT or to implement a "soft scope" in the web UI) should be easy to handle.

BTW, if you think all that is overkill for HVAC control, it is. I'm using it as a learning experience to get more familiar with software development.
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Last edited by NiHaoMike; 11-25-13 at 03:38 PM..
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