Answer to "How does one use the PT100 Amp Board with a 3.3v controller, eg RADDs"The issue is most 3.3 volt 32-bit controller chips are only 5 volt signal tolerant on their digital pins. Placing more than 3.3 volts on an analog pin will damage the chip. You may be able to limit the PT100 amplifier output signal’s voltage to a max of 3.3 volts by using a moderate resistance in series resistor (60 to 100 ohms 1/4watt) on the 5 volt powered PT100 amplifier signal output to limit the output current with a small signal diode (e.g. a 1N914) connected to the resistor’s other pin in reverse biased fashion to the 3.3 volt supply of your 32-bit controller board. A 60 ohm resistor should limit any current from the PT100 signal output at 5V to the 3.3V supply via the diode to 20 mA protecting your 32 bit electronics.