What is it?

Optically isolated interface board that allows a Raspberry Pi, Arduino, BeagleBone or any logic level digital input that works with the output of an opto-isolator and 10K pull up resistor to monitor a 24V AC/DC signal common HVAC systems and on irrigation solenoid valves. It has a built-in LED to make it easy to see when a signal is active and screw cage connectors for easy hook up. It has a rectifier and filter capacitor to convert AC to DC and hold the output stable so the receiving microprocessor does not need to process a pulsating signal. Two pictures show an actual unit on our Holey DIN Rail Plate connected to a 3.3 V PU and with a 24VAC transformer connected to the input in on and off states; the output gets pulled below .1 V when the 24 VAC transformer has power.

Why did you make it?

I often use a Raspberry Pi, Arduino or BeagleBone to monitor and control systems in agriculture and industry and wanted a versatile interface board that could be used in a wide variety of prototype and low volume situations. This is that board setup to accept a 24 volt AC or DC signal.

What makes it special?

While this version comes setup for 24 volt signals, there are two large footprints on the input that allow use of resistors capable of dropping a wide range of input voltages. By happy coincidence the mounting holes are very close to the hole distance on a Phoenix Contact 1201578 Din Rail Adapter allowing DIN rail mounting. This is not listed as an official feature because while the holes are close enough to work, the leads of the components are pushing against the adapter which may or may not be a problem. If we update the board, the size will increase a bit and components will be moved to properly support the DIN adapter.