robosang WROTE:Well.... a photo of the whole setup should clear the question. Might be routed via other wiring path.
shaneb24 WROTE:when i ground the two device's( The Velleman K8023s with PSC28A) , the led on K8023R turns off and unresponsive ..
Yes, I agree with robosang too. How you (o.p.) connect the supply to K8023R and the PSC28A is very important. If you read the schematics carefully, the DC supply of sender 8023S is fed from the 8023R receiver and the communication signal is riding on the DC lines(8.8V). The GND2 on the 8023S should be floating as you can see from the cct diag that it is labled as GND2 instead of GND.
If the GND of PSC28A is somehow shorted to the GND of 8023R unintentionally (through the 3-pin power plug). The whole thing would not work if the GND2 is connected to the GND of PSC28A as the signalling would be effectively shorted to ground.
Allen