Matrix Orbital LCD0821 Legacy - Manual (Page 12)

LCD0821 rev 2 12
2.2 General Purpose Output
The LCD0821 has a general purpose output which can be used to control relays or other electronic devices.
This allows external devices to be turned on or off using your PC or controller and software commands.
(See sections 5.1.5 and 5.1.6 for the command syntax.)
The output is wired as shown in Figure 2-9. The + terminal is connected to the module positive supply, the
– terminal is connected through a 240 ohm current limiting resistor and the electronic switch to ground.
+ 5 VDC
240 ohm current limiting resistor
load
+ -
Figure 2-9 General Purpose Outputs
Maximum allowable current is 20 mA, which is enforced by the current limiting resistor. If the device being
switched has a resistance of 240 ohms or more the corresponding resistor may be shorted. Solder a small
jumper wire (wirewrap wire is good) between the two feedthrough holes as shown in Figure 2-10.
GPO
+ -
240 ohm
resistor
Jumper
Figure 2-10 Bypassing 240 ohm resistor