#04-4, M1S: Four Opto-inputs, Common Ground
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Function: Four opto-couple inputs with the '-' terminal connected to the system ground, independent '+' terminals
Form factor: M1S
Category: Input module
Special needs: ---
Power requirements: 5V/40mA
If no external resistor is added these inputs activate at about 2V. Forward current should not exceed 10mA, and this caps the maximum input voltage at around 5V. Add external resistors if you need to apply higher input voltage.
Note that these are not "isolated inputs" – they share the ground line with the rest of your system. Still, the optical stage isolates your system from noise, ESD, spikes, and other external influences.
There are four green LEDs which are connected to four control lines. LEDs light up for the LOW state of control lines (i.e. when current passes through the diodes of the opto-couples).