The generic heating / cooling controller (hcctl) is a flexible bang-bang controller based on an ATTiny25.
The controller will accept 4-20mA input if the input is shunted by a 50Ω 1% resistor (2 x 50Ω 1% resistors is a practical implementation) and the 4-20mA sensor is wired between nominal +24 and the input pin. Note that 4-20mA sensors may operate properly on less than 24V (the one used here is a DIN rail mount that works for 10-24V).
To demonstrate the capability, a Pt100 RTD is connected to a 4-20mA converter and then to a hcctl test module (see above). The test module is driving a small incandescent lamp which is clipped to the RTD to provide a cycling test.
Continue reading 4-20mA Pt100 input for the generic heating / cooling controller