4ch Optoisolator board
Built around 6N317 wich have 10Mbs throughput, logic output and reasonable price. Board is single sided to facilitate diy projects. Resistors R1..R4 should be chosen according to input voltage, 5V=220R, 12V=560R, 24V=1K5. Other values can be calculated R=(Uin-1,5)/I, where I = 5..50mA. Different inputs can have different voltages/resistors. Positive polarity should be connected to resistor side of input. Negative voltages across input greater than 5V will damage optocouplers. C1..C4 should be 100nF plastic or ceramic. These are for power conditioning.