HVAC Controls.

I have been working for a while in some spare time to build my own controller for the use in building HVAC applications. I wanted to prove a few of the circuits so I squeezed as much as I could on a 10cm x 10cm board.

So this is very much just a proof of concept to check that the elements work.

SMD parts were soldered using a mini oven from Argos. I have to confess this is my first time using this method and on my first attempt I heated up the board too quickly which caused what can only be described as electronic popcorn.
The second time result is not perfect but a relative success. I set the temperature manually as required by the SMD paste temperature graph every 30 seconds.

The board has five universal inputs, selectable as follows using the jumper adjacent to each input:

• Digital input.
  
• Current 4-20mA input. Note that loop to be externally powered.
  
• Thermistor Input.
  
• Voltage 0-10vDC (Not PWM).
  
  

Four analogue outputs 0-10vDC (20mA max)

Four digital outputs via relays.

The board has a set of female headers on the back to plug the Espruino into. Note that my Espruino has the pin headers mounted in a downward direction.

I have tested some of the very basic functionality.

• Thermistor reading but not as stable as expected. Further investigation required.
  
• Only two of the analogue outputs are working correctly. Suspect this is down to the tiny resistor network components not soldered quite right.
  
• Only one relay soldered on so far but working.
  
  

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