8 channel relay interface for party lighting

To control the party lighting, I designed this relay card in 2004 shortly before a party. It can control 8 power outlets via the parallel port of a computer.


In the tinkering box I found some Finder relays and suitable optocouplers, I had to order four more relays. Each relay can handle 250V / 10A. The suitable PCB layout was drawn in half an hour.

Picture: Relay and layout draft

Around mains voltage conducting tracks large isolation distances are used.

Picture: PCB layout

The PC software is coded in Delphi.

Picture: Software

With the program you can switch all channels individually, or set a sequence in the 8x8 matrix. The first row of boxes sets whether the outputs are affected by the settings in the matrix. If not, you may switch the respective outputs manually. The bottom row with the radio buttons sets how long the set blink sequence is. The speed can be adjusted, or adapted to the beat of the music via a beat counter. With the 9 buttons to the right of the matrix, you can load stored programs and call them up and change them with a click. The L next to it stands for load. After loading, the respective program can be selected by clicking on the large button.

All preparations are completed. The delivery of the components is still missing to finish the assembly.


The board is etched and half assembled, I will finish the enclosure tomorrow after school at my grandpa's house. Reichelt had some delivery problems, but let's hope that the package will arrive on saturday. The software has also changed a bit, the buttons turn green when the output is active, so you are able to see if the relays are switched from some distance away.


The case has been finished for a long time and at the party the device worked fine with 4 channels. Unfortunately the delivery was not in time, but I could get the missing cables at the hardware store. Today I had some time to finally connect the last cables. Now all 8 channels can be used.

Picture: Relay
Picture: Overall picture
Picture: Complete view
Picture: Bottom side of the board

To increase the power handling capacity, the mains voltage conducting tracks are tinned. Each channel is individually fused with a 2A fuse.


For power supply the transformer was intergated.

Picture: Assembly with transformer
Picture: Built in transformer