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Does anyone know the protocol of the Honeywell DG115EZIAQ TrueIAQ sensor system. This is an outdoor temperature/humidity sensor control system. It has a two wire sensor with 24VDC across the pair and a pulsed waveform superimposed upon the DC. I added this question to clarify my needs of my first post "Protocol Analyzer in software?". Thanks in advance.

EDIT: The data is updated once each ~1second. I assume it is a response from the sensor only, however that is just a guess.

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I don't know the exact protocol of your device, but does it appear to be similar to the Dallas/Maxim 1-Wire protocol?

http://en.wikipedia.org/wiki/1-Wire

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  • \$\begingroup\$ I looked also at that. It is very similar, but the pulse width and timing don't line up. I gave you +1 because I think that is an excellent reply. \$\endgroup\$ – SteveR Aug 18 '11 at 21:14
  • \$\begingroup\$ I did some more quick digging on Google. What about the CEBus? en.wikipedia.org/wiki/CEBus There were some references to this CEBus and Honeywell products. I'm finding it hard to find more than cursory info on this "CEBus" though...wiki does mention something about 100uS timing. Protocol info seems somewhat guarded though. Hope this might help you out some more. \$\endgroup\$ – dext0rb Aug 19 '11 at 16:01
  • \$\begingroup\$ CEBus is a frequency modulation type protocol, something similar to FSK. It is used for power line communication, like X10 only better. That is not what I have. My pulses are of constant amplitude and pulse width. You got me thinking on the 1-wire, I keep thinking this is some sort of variant of that. The problem is, my samples do not begin with a "reset" pulse of 480µs as the protocol calls for. My first pulse is actually the smallest PW of only 105µs. Thanks again for your help! \$\endgroup\$ – SteveR Aug 19 '11 at 21:03
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Based on the way the sensor is wired where power and communication are on the same two wires I would guess that the sensor is some variant of a 4-20 mA current loop and that the digital communication may be Hart protocol. Does the voltage level of the signal change with varying conditions? What is the peak-to-peak voltage of the signal?

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  • \$\begingroup\$ The pulse has a p-p of 20 volts. The range is +3.4V to +23.4V. While searching Honeywell, I see they use a lot of 1wire protocols, as dextorb suggests, however the pulse timing is much faster than anything I see in 1wire documentation. They also seem to have there own chips, but also use some Dallas/Maxim as well. The 1wire protocols I have read seem to all have a negative start pulse of 480 µs, my start pulse is 105µs. \$\endgroup\$ – SteveR Aug 19 '11 at 14:17

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