[SOLVED] Output analog temperature signal

[gaute]

Hi All,
I've currently working on some new nodes to control my central heating system. First I'm going to explain my system:
We have warm water running in the floor of all our rooms, with separate valves for each room. I'm currently building a temperature node for each room and a central node with relays to control the 24v valves. I'm also thinking of integrating a lcd display into the temperature node, to set the target temperature.
At the hearth, we have a earth to water heatpump that heats the water to a target temperature. It has a relay input for some of the controls and it is possible to connect a analog external room temperature sensor to adjust the heating.
I'm trying to build a node to control the heatpump. The relay inputs are quite simple, but I don't know how to make the analog temperature signal. I think I need some kind of D/A converter.
Does any of you have any suggestions?

Thanks

[papa]

gaute, thanks for reading & posting at this DIY home automation forum. Though I'm not sure I understand what you're asking for. Putting this post together with your previous question about multiple DHT11 sensors on a node, I can venture a guess:

Is this something like your current setup / situation? Each room (or zone) has a thermostat (analog?) whose wiring connects it to a central control board. Central heat pump with valves for each room, with a nearby central electronics that receive thermostat info & activate relays that control the 24v valves (DC?)?

Perhaps you are "working on new nodes" because the current setup stopped working or because you want to add more precision or automation. From what you describe, I cannot tell if our work here with wireless nodes would help you or not.

If I was in what I guessed to be your situation, I would want to do a few things (& maybe you already have) 1) Try to be very knowledgeable about how your heating system works & how I could adapt things without harm. (I personally would need much research.) 2) Search the internet for "Arduino control of heat pump." (Google listed several possibilities.) 3) If your thermostats' wiring to central control is intact, I would consider taking advantage of the wiring & maybe the existing thermostats. I would want to test if a thermostat & an Arduino can communicate at those distances (lengths of thermostat wires). Arduinos have analog connections as well as digital. It might be possible to wire your thermostats (or other thermostats, analog or digital) to one or more Arduinos whose programming could activate relays to keep room temps in a target range.

Another possibility is a DHT end node in each room that uses the thermostat wiring to activate the relay for the room's valve. I would want to test if the node could do this over the longest thermostat wire. If that worked, it might open possibilities where this forum's information could help perhaps alongside other sites ideas about Arduino control of heating systems.

[gaute]

Hi,
thanks for your reply.

I have the room sensors pretty much figured out. Like I described, I have replaced the original thermostats with an Arduino with DHT.

What I'm working on now is the controllcircut for the heatpump. It has two possible inputs; one is an external room temperature sensor (analog), and one is for lowering the target temperature (binary, on/off). My question is if any of you know how I can output a analog signal (to a transistor or something) to "fake" the room sensor? My target is to let the heatpump think it has a room sensor, when really I calculate the temperature using openhab.

I hope this made more sense.. I attached a sketch to simplify...

[papa]

You say you replaced the thermostats with an Arduino using a DHT sensor & are now working on "controllcircut for the heatpump." In your sketch, above the device with "analog connector" & temperature lowering connector, you have the label "NEW ARDUINO." If you really have a new Arduino as the basis for the control circuit, why do you need an ANALOG temperature? Why can't you just program the "new arduino" to respond to the DHT22s' DIGITAL temperatures from the room Arduinos?

[computourist]

Hello Gaute,
as I understand it you need an analog voltage that corresponds to a number you send thru Openhab.
Arduino does not have a D/A converter on-board. You could connect an external D/A converter to provide this function.
Another -and much simpler- way is to use the PWM (Pulse Width Modulation) function that is available. This function generates a block-signal with a duty cycle that varies between 0 and 255.
By using a low-pass filter (RC-filter) you can transform this into a DC voltage. This process is slow (too slow for audio) but given the slow reaction times in a heating system this should pose no problems.
Search the Internet for "Arduino D/A" and you'll find sites like this one.

BTW: device 32 to 40 in the gateway are designed for PWM output, so you would only have to adapt the end node code for this to work..

[gaute]

Hi,
Sorry Papa for my poor explanation skills. The "heatingcircuts" and the heatpump is not interacting with eachother, this is partly what I'm trying to achieve.
Thanks, computourist, exactly what I was looking for! I did not know you could use the PWM output that way!

I will write a post explaining my whole system when its complete. I'm also building a node to control the house's central ventilation system, almost the same way as I control the heatpump.

Thanks!

[papa]

Glad it worked out with CompuTourist's help, gaute. He's a treasure.