A new PWM controller

[Hugh Norwood]

I'd be interested in which microcontroller you intend using, Richard. I was interested to see the Arduino has PWM outputs, but then I found the maximum repetition rate is about 490Hz, which is really too low for small motors. So I shelved that idea.

My offering could easily be changed to limit the maximum voltage by supplying the output to the MOSFET through a voltag regulator (eg a 7805)

Although, come to think of it a complete low-voltage desgin would be possible as the 7555 will run from 5V.

Actually, I've experienced no problems with running KATO chassis against the "older" chassis with this controller.

[Graeme Dunbar]

That's partly correct. The standard Arduino rate using the built in "analogWrite" function is 490 Hz, but it is possible to bypass this. However  there is a compromise to be struck between using the Arduino environment where the hard bits are hidden and performance when controlling the hardware directly. It is possible to make the Arduino generate a TV text overlay signal so it can handle higher frequency I/O, but it ties up most of the resources. (I've used that on the ROV (underwater robot) exhibit I designed for the Aberdeen Maritime Museum.)

PICaxe might be a better bet, but at the cost of losing some of the user- or beginner-friendly elements.

Then of course you could go all fancy and use an mbed microcontroller and control it from an Android phone!
http://www.youtube.com/watch?v=rsEBQiMl7Zo

(But the mbed controller is not aimed at the same market as the Arduino which is for real beginners.)

[Hugh Norwood]

Things have got a lot smaller from when I used a DEC LSI-11 in my research back in the late 70's....
Ah, but the joys of assembler programming!

[Hugh Norwood]

I would like it if you kept us posted on your progress and experience, Richard