What is it?

Note: the PCB has been updated, same circuit, same connectors / connections, similar form factor. See below for more details. 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 in 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. Pictures show an actual unit on our DINVESA 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. Details on PCB update: the board and mounting holes were made slightly wider so the a DIN clip can be directly mounted to the board. Also most of the footprints were converted to hybrid through hole / surface mount formats that accept a wide variety of parts. Also expansion connection point have been added so a future multi-channel expansion board can be connected.

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. The mounting holes line up with a Phoenix Contact 1201578 Din Rail Adapter allowing DIN rail mounting. And a LED makes it easy so see if the input is active.