Motor Decoder.

Following many requests for a DIY motor decoder that can be made as easily as the DIY function decoder I have now developed a very basic DIY motor decoder based on the 12F629 processor and DIY function decoder circuit. While it is very basic and has no function outputs and very limited CV and operating mode support it probably has better performance than a lot of the basic 10 pound decoders that you can buy in the shops if all you need is very basic functionality, and you will have the satisfaction of building it yourself. While the electronic circuit is mostly my own design, the firmware is just a port of Heiko Schroeter's Z-Gauge decoder firmware so still contains many of the bugs and shortcomings of Heiko's decoder.

If you want a better motor decoder I would recommend that you either make a MERG one if you really must make your own, or better still buy a Zimo which has really very good performance which I could never match in a DIY design because of both size limitations and the time required to develop the first class motor control algorithms.

The motor decoder can be made in about half an hour with practice, and can drive up to 1.6A which should be OK for most locos. It includes built in overload protection and thermal shutdown, but it probably won't last for ever if you abuse it. Electrical performance will be as good as the DIY function decoder so it should read packets quite happily on dirty track - which you won't get from a 10 pound shop decoder.

copyright Ray West

CV Default value Range Description Notes
1 3 0-127 Short address 0=DC only (address zero is broadcast address)
2 20 0-255 Minimum speed at speed step 1
3 1 0-15 Acceleration delay
4 1 0-15 Braking delay
5 200 0-255 Maximum speed at step 28
9 160 160-167 PWM frequency 160=2KHz - 167=15Hz
17-18 0
Long address
19 0 1-127 Consist address
29 2 0-255 Configuration bits Default is analogue DC rather than Brake on DC and 28/126 step
65 20

Colour key

Supported CV Table for V0.1 firmware
Not as per NMRA recommendation

Not NMRA recommended default


All downloads are now available from the Downloads page.

Page updated 5th July 2010.