MK131 Traffic Light Kit modification for UK

We received this nice tip from Dr Ian Jutting and wanted to share this with you!
It is a nice modification to change the MK131 traffic light to the British traffic light sequence:

As a resident in in Great Britain, I have enjoyed constructing Velleman kits over the years as well as building my own electronic circuits for various functions.

I have just obtained and constructed the Velleman Traffic Light Kit. As usual with Velleman kits, it worked first time! However, I noted that the traffic light sequence is of the Continental pattern, not the British pattern. This is hardly surprising as of course the kit was developed at your headquarters in Belgium.

However, I decided to analyse the circuit. I found that by adding just two diodes designated D22 and D23 to the diode switching matrix, I could easily convert the switching pattern to the British traffic light sequence:

This kit gives an interesting insight into the use of decade counter digital switching techniques using a signaling diode matrix to create the various output switching requirements.

  • The kit simulates the continental traffic light sequence:

  • The British Traffic Light sequence is slightly different:

Conversion to British TL sequence can be achieved by adding two extra diodes, both 1N4148 designated D22 and D23 soldered onto the rear of the circuit board.

The datasheet for the CD4017BC Decade Counter was reviewed, particularly the output timing cycle.
(From Fairchild Semiconductors Data Sheet for counters CD4017BC / CD4022BD)

From this timing diagram, it was possible to deduce the Continental Traffic Light sequence output, also determine the requirements to achieve the British Traffic Light sequence.


The two additional diodes, D22 and D23 were conveniently accommodated on the rear of the circuit board, behind the connections of the diode routing matrix.