Anindo Ghosh

So I'll let you in on the secret of why I know this camshaft stuff: The light sequencers which would become obsolete in the USA or parts of Europe were often bought at scrap value and configured for use in advertising signs in India. They were operational here for perhaps decades after they had become antique curiosities in your part of the world.

When I was in middle school, I got a chance to fiddle with one of those setups belonging to a family friend. It had stopped working - merely because nobody had replaced the brushes for a decade or more, and they'd worn down.

I'm about to appear very aged by this comment:
The popular camshaft sequencer designs used the camshaft as the common, and fairly robust springy "brushes" as the contacts.
The advantage used to be that the contact brushes and camshaft were both self-cleaning, just by the friction and its polishing effect.

One big DISadvantage of high power camshaft-sequenced advertising signs was that, depending on the power involved, the repetitive arcing could ruin AM radio reception for everyone in the vicinity.

3V motor and some kind of single-chip PWM + speed control part would be great. If you can fit it in your budget, TI has some low-cost, low-current single-chip motor controllers IIRC, that do the PWM, back-EMF readout (including readout of measured speed via SPI, I believe), and even bells and whistles like motor speed ramping.

Next choice, 3V motor, PWM for speed control, and back-EMF

That is unless your device has a boost convertor already used for something else, and you have an underutilized 6V / 9V rail with power to spare :-)

While I don't have the answer about your specific diode, often two manufacturers, and even two "vintages", of an identical diode, will have different epoxies used: Different thermal conductivity, more advanced polymers etc., and the physical package dimensions will change.

Also, thermal insulation is not a desirable parameter of a diode's package epoxy, thermal conduction is: You want the heat from the junction to dissipate out as fast as possible - otherwise that's how thermal runaway happens.