AAAAH, THANK YOU! Now the data sheet for, say, the 2N3904 makes PERFECT sense when it says "100mA as switch" yet has a max dissipation of 625mW! Sweet. That's a lightbulb moment, right there.

I'm going to make a wild guess that my 555 output will go from L to H rapidly enough to prevent any problems (none so far, and I'm 'shock testing' this with a much higher load than it'll ever see).

I do mainly audio electronics, so this end of things is still a little unknown to me. I guess that's kinda backwards - being able to bias a transistor for audio use but not knowing a lot about switching characteristics, ha ha!

 

It seems as if you have a lot invested in this solution, already. Are you interested in alternatives at this point?

 

It seems as if you have a lot invested in this solution, already. Are you interested in alternatives at this point?

Yup

There are some big drawbacks with my plan...if you trigger the H bridge's other side while the 555 is discharging, you'll burn it out, is one....

Any ideas on how to do this with the reed switches, AND a manual override that isn't overly complex (as mine is)?

 

Yep! Instead of using an H-bridge, use latching DPDT relays. There is one on Digikey that goes for about $2.00. This relay has two coils, and can be operated by two electrical switches. A momentary pulse results in the relay switching to the corresponding position and staying there.

Forgive the crude drawing, but in general the hookup is as follows. On the left, in red, are two reed relays. Other momentary switches can be wired in parallel to each of the reed switches for manual operation.

The center of the diagram shows how I would wire latching relay.

The right hand of the diagram represents the Tortoise switch machine. I've labelled the pins. One of the accessory switches is used to light the indicator lights. The other accessory switch can be used to power the switch frog.

Note that I've indicated three different power sources. Some of them can be combined, for example the relay and LED power. All three could be combined in fact.

 

Very nice, DJ, thank you! That looks a lot simpler, and that means easier to understand and probably more dependable. I really enjoy learning all the special uses for transistors etc., so that's not wasted time, but I think I'll talk him into the latching relays, ha ha. Cost wise, it's probably even cheaper!

Would you be able to wire up a momentary toggle in parallel with the reeds for 'manual override'? Looks like it should work.

 

Yes. You can wire any momentary electrical switch in parallel with or in replacement for the reed switches.

 

I take you you do model RR work too?

I was thinking "flip-flop" initially, but didn't move that way because of the ground issue (a FF isn't "DPDT"). Funny, the solution is a 'mechanical flip flop'! The only other latching relays I'd found were far more expensive, and he said no - these are economical! No need to re-invent the wheel, ha ha.

 

Yes, model railroader here! Although I lost my layout a few years ago due to family expansion.

Good luck!

 

Yes, model railroader here! Although I lost my layout a few years ago due to family expansion.

Good luck!

Thanks, you helped solve a 5-yr old issue, and now the old boy can have his 5 control stations, lol. Appreciate you offering to help!