James:

Here is a schematic with the additional components to support dual level 6V and 3V drive to the motor. Whilest I think this should work please note that I did not build the circuit up to test it. This should still be low cost to build.



You could consider one of the newer style regulator packages that would make your dongle circuit board a bit smaller. See below. With a regulator like this and use of surface mount components the dongle would be really small!!



By the way......since the existing circuit board already has an LM317 on it is it possible for you to just change two resistors there to get that LM317 to output 6V and 3V? Or does the existing board need to be left intact so that 12V/6V motors can still be used?

Posting links and pictures on the forum was described in detail in this previous thread last year.

Michael Karas