Velleman High-Q Velleman-kit K8023, Illustrated Assembly Manual

10 

14. Operation

Operation 

1. Control  section  (P8023S):   

 
Both PCBs are connected to each other by means of two wires, VTX+ and VTX-. They supply power to the 
control board and carry the data signal. This signal contains information regarding the status of the 10 inputs.  
Filtering and regulating of the power supply is performed by VR2, together with C15, C12, C13 and C14, 
which also suppress possible oscillation of the voltage regulator. 
The micro controller continuously monitors the status of the inputs, and switches T2 according to a custom 
developed serial protocol. This allows a current to flow in the VTX wires.  LD12 also lights allowing you to 
check the operation of the system. 
 

2. Receiver  section  (P8023R): 

 
The receiver end also contains a power supply section.  Diodes D1 to D4 rectify the incoming power.   
Voltage regulator VR1 and the surrounding capacitors make sure the control part receives a regulated 10V.  
From this 10V, R12, ZD1 and C8 derive 5V DC to supply the microcontroller. The actual receiving part 
consists of D6, D7, R14, R15 and T1. The current variations in the VTX-lines cause a  
voltage drop over R15, which is filtered by C3 and amplified by T1, before it is fed to the micro controller.  
Reception is indicated by LD11. The microcontroller analyses the serial signal, and puts the corresponding 
outputs high or low.   
Because the microcontroller cannot sink large currents, we added IC2 and IC3, which provide open collector 
outputs.