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TTU-12x0 Hardware & Installation Guide - PULS Wiki
https://puls.calamp.com/wiki/TTU-12x0_Hardware_%26_Installation_Guide
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3.5.5 Ignition and Inputs
The TTU-12x0™ provides up to 5 external inputs and one internal. The external inputs are protected from typical vehicle
transients and can be directly connected to most vehicle level logical inputs from 4 volts up to the vehicle power input level
(typically 12 VDC). Their input impedance is approximately 10kΩ. One of these inputs is dedicated to sensing the vehicle’s
ignition status to provide for flexible power management. The other two inputs may be used to sense vehicle inputs such as
cooling unit operation, a hidden driver “Panic” switch, taxi on-duty/off-duty meter status or many others.
The ignition input is pulled to ground through the 10k resistance, where the other inputs can either be normally High (i.e. pulled
to +12v through a 10kΩ resistor) or Low (i.e. pulled to ground through a 10kΩ resistor). Input 1 is always biased low, while
inputs 2-4 are biased high. The diagrams below show how to connect the inputs in both a high and low-biased configuration:
