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Custom built digital power base misbehaves

1558 Views 9 Replies 6 Participants Last post by  anttu
I've managed to build an scalextric digital power base using the schema and code from Electric Images.
Everything seemed to work fine with one car running on a simple oval track for at least 5 min. After that I added a straight lane changer and that's when confusing things started to happen.

When the car goes over the "eye" of the lane changer, the car stops immediately and leaves buzzing on the track (a little like putting an analog car on a digital track). The lane changer also sounds strange (tr-tr-tr-tr), like it tries to flip the lane, but can't. If I lift the car away from the track and wait a few seconds and then put it back, everything is fine until I run over the lane changer again...

The thing is that I can get it working by adding a small resistor in series with the 12V power feed to the track. I actually noticed this by accident, because I removed the fuse for the track power and put an amp meter in its place (because it was the easiest place to break the circuit on) to make some measurements, but then everything worked fine
I then put back the fuse, and the problem was there again
Also tried a short cable, same thing....I almost went nuts! What could be the difference between using the amp meter and a fuse/cable?? Hmm...the shunt resistor! I then tried replacing the fuse with a ca 1ohm 5W resistor, and everything worked fine again!

Can someone explain to me what's going on here!? I'm confused. Why isn't this taken into account in the schema on the Electric Images site?

Btw, I notice that the schema for the original 4 car power base from Scalextric, found here, does include some resistors in series with the track circuit (R15, R16, R18), but I understood from some other forum thread that these are used for current monitoring by the controller. Or can they be there for some other reason too?
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I think you may be the pioneer in this area. Hence the lack of response.

Most other folks buy new/used PBs and get them modified either by self or one of the pros on the forum.

Maybe someone else will be able to give you an answer.

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