Self accelerating reed switch magnet spinner.

[TinselKoala]

I had to take it apart to reglue a magnet, so here's the underside view of the rotor, showing the assortment of magnets. It's all I had available when I made the original Bedini SMG that I am recycling!

[TinselKoala]

Hey TK:

I am really tired today so all I can offer is a Google search that looks pretty good, "555 falling edge trigger."  You might find some good circuits that demand as input a brief negative going pulse.  That might no be too compatible with what the comparator output is doing in the sense that it stays low for a "long" time.  However, to get around that you just need to put a small cap between the comparator output and the 555 circuit that expects a brief negative going pulse to trigger the monostable.  So the cap will couple the falling edge to the 555 trigger input.

Also, you put a pull-up resistor on the 555 trigger input.  (You may also want to put a diode connected towards +12 volts to snub out any over-voltage on the 555 trigger input when the comparator output transitions from low to high.)

So when the comparator output goes from low to high, the capacitor has roughly +12 volts on both sides and it's not charged.

Then when the comparator output goes from high to low, the 555 input sees that high to low transition and that triggers the 555 monostable to flash the second LED.   Then while the comparator output stays low the pull-up resistor charges the cap and the 555 is "satisfied" because it sees a HIGH on the trigger input again - i.e.; the 555 trigger input (possibly) only wants to see a very brief negative pulse that is much shorter in duration than the monostable output that flashes the LED.

Typically it's a very tiny capacitor that will do the trick.  Perhaps a 0.1 uF cap.  Then you might want the falling edge trigger to be low only for a few hundreds of microseconds.  So you choose an appropriate pull-up resistor using the RC time constant.

It's a "quasi kluge" that should work just fine, and all you need to implement it is a negative edge triggered 555 monostable circuit.

MileHigh

That's not a quasi-kludge, it's a fullblown grownup kludge.

Did you miss my post above, Analog Op-Amp Man?


The TL082 has two opamps in it and all that is needed is to reverse the inputs, put the reference voltage from the setpoint pot into the non-inverting input and the sense coil into the inverting input of the second opamp. It seems to work fine, so far.

[TinselKoala]

So here's yet another schematic, showing how to hook up the second op-amp in the TL082 to do the trick. I just use the same 4017/555 combo for now but will make another setup with a 556 and a second 4017. So the chip count will be 4, but most of that will be for the strobes.

[synchro1]

@TK,


      This circuit looks like it may spring to life by lightning strike. Watch it now! Maybe your dog can help lick clean what's left of the peanut butter from inside the lid.

[MileHigh]

TK:

Ah! Ha!  I get it now.  It did not register with me that you get two op-amps for $0.71!  So there is your logic inverter and you can trigger another 555 and do your divide by four.  I assume that you are getting ready to wrap this one up soon but are you sure that you need two CD4017 chips?  You can't do it with just one counter? Don't mind me!

Notice your pulse control logic is is fixed at +12 volts but the power to the drive coil is like a free range chicken.  So you could play mad scientist and raise the potential on the drive coil to some really high voltages if you wanted to, and put on a Kevlar vest and some Gucci designer mad scientist goggles.  Just go insane!  (remember protection diodes)

I think you might need to route the coil energy into a battery or something if you go the insane route.

Another phenomenon that you might want to explore is this notion that sometimes the current flowing through the coil never stops flowing between energizing pulses.  Like man, it's constantly circulating.  In some pulse motor setups with a conventional diode discharge in to a charging battery the experimenter might not even be aware that this is happening at a high RPM.  That actually represents a danger.  You put your pulse motor on high speed, the phone rings and you go into another room and start chatting.  When you come back 20 minutes later your coil is a red hot blob about to eat its way through the table.

MileHigh