#54, M1S: Four Dry Contact Inputs
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Function: Four dry contact inputs; external switches should be installed between the input terminals and the system ground.
Form factor: M1S
Category: Input module
Special needs: ---
Power requirements: 5V/40mA
Unlike Tibbit #04, this device requires no external power to control its inputs: Shorting an input to the system ground will activate this input and set the corresponding control line LOW.
Note that these are not "isolated inputs", even though they feature opto-couplers in their circuitry. Still, the optical stage isolates your system from the noise, ESDs, spikes, and other external disturbances.
Combine this Tibbit with terminal block devices – #20 (nine terminal blocks) or #21 (four terminal blocks). Note that this Tibbit does not provide a ground line so you will need to "steal" the ground elsewhere. The ground is immediately available on terminal 5 of Tibbit #20.
There are four green LEDs, which are connected to four control lines. An LED lights up for the LOW state of a control line, i.e. when the corresponding input is shorted to the system ground.