User's Manual

Houston Radar DC310 User Manual
Page 25 of 27
Appendix A: Hooking up to the trigger outputs on the radar
The DC310 radar features two “open drain” outputs. The device used for this purpose is the On
Semiconductor relay driver NUD3124. The output configuration of this device is shown below
(from the On Semi datasheet).
The two outputs O/P1 and O/P2 are brought out on the radar connector pins (see IO connector pin
out in manual for connector pin numbers).
This device can sink 130mA of DC current at up to 28VDC.
However, these are low impedance outputs, which means that you must externally limit the
maximum current that will flow into these outputs to 150mA at the worst-case head voltage. They
may be parallel together to increase this value to 300mA.
There are two ways to ensure this:
1. Connect an output device that is rated to draw no more than 150mA at your supply
voltage (+Vhead). This device can be powered up to 28VDC. For example, this can be a
12 or 24VDC relay coil rated at more than 150 mA coil current or
2. Connect an external resistor in series with the output load and the O/P1 or O/P2 pins. The
value of this external resistor should be calculated as follows (ohms law):
R (in K Ohms)= (Vhead –Vload drop)/150
Load rated to draw
max of 150mA at
+Vhead max
+Vhead
Load
+Vhead
Resistor
Load
Method 1
Load
Method 2