Circuit to stay switched on after being triggered once

Yep, that's exactly what you are looking for. You can make one out of two cross-coupled NAND or NOR gates. Or, you could go back to the "good old days" and make a latching relay. Just get a relay that has a spare set of NO contacts (besides whatever you need to control your load) and use those to drive the relay coil in parallel with the original trigger driver. The reset switch is then just an NC pushbutton in the coil circuit.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

Thanks Bob

Am I right in saying that and S-R flip-flop made with NOR's will trigger when the inputs go high, and one made with NAND's will trigger on going low?

I think I have some NAND's with schmitt triggers on the inputs somewhere, so I'll use those.

Regards, Mark

Why not an SCR?

Sorry, I don't know what an SCR is, would you mind explaining?

Regards, Mark

Google SCR

Yup.

Cheers! Rich

Perfect! :-)

Remember to use pullups (4K7 ~ 10K or so) to +Vcc, and the switch to ground.

Have Fun! Rich

Ah-ha - Ididn't expect to find any results easily. Another name for a thyristor. Always wondered what they were for. Now I know.

Very cool, but I have NAND and NOR gates at home.

Regards, Mark

Ah, yes of course, thanks for reminding me.

Cheers Mark

Under the category of etc, a relay circuit:

Vcc + ---------o---- +---o---^ | -- Ve --->|---+-----| /|-----+ | |/ | | | -- | | Relay | | | +------|

Hello Mark,

You can also use two Schmitt inverters, 74HC14 for example. Connect a 1M from input U1A to output of U1B, then another from the output of U1A to the input of U1B. Then you still have four more inverter to rent out. If your supply voltage is higher than 5V use a CD40106.

Sending a pulse to any one input will flip this into the desired state and it stays there. Just remember, all of those solution will come up in an undefined state when you power it up. Unless you provide a reset of some sort.

Regards, Joerg