HHB comm UDP-89 - Manual (Page 46)

Appendix 1 - Connector Pinouts
45 UDP-89 User Manual Version 2.1 www.hhb.co.uk
Electrical characteristics
Both inputs and outputs are internally opto-isolated. The inputs
are protected against over-voltages.
Inputs
The inputs simply require a short-to-ground for activation.
Outputs
The outputs are open-collector, and go low when activated.
Loads such as LEDs may be connected externally with a suitable
series resistor, and returned to the +ve terminal of an external
PSU. The maximum current deliverable by the opto-isolator’s
transistor is 50 mA. (The –ve side of the external voltage supply
should be referenced back to the UDP-89’s 0 v on pin 6.)