You could use an External switch or Sw1 to be the input switch, an External switch can be a switch from other circuit or relay, and the Sw1 can be a switch on board or an independent switch.
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I tried switching R1 and S1 and that worked, but I need to keep one side of the switch connected to ground. I haven't tried the suggestion by ScottWang yet. Would prefer to do it without additional components if possible, but that may not be possible. Do you guys think that using a transistor is the only simple way ? Thanks for your help.As said,,, increase R2 to say 100k and swap R1 and S1...
I'll be running 12vdc through the circuit and probably 8vdc to the switch. I have some Mosfets and BJT's. I don't think I have any that will trigger at that voltage. Does anybody know a particular model # for the transistor that might work ? Thanks.You could use an External switch or Sw1 to be the input switch, an External switch can be a switch from other circuit or relay, and the Sw1 can be a switch on board or an independent switch.
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What do you trying to connects the 8vdc to the switch?I'll be running 12vdc through the circuit and probably 8vdc to the switch. I have some Mosfets and BJT's. I don't think I have any that will trigger at that voltage. Does anybody know a particular model # for the transistor that might work ? Thanks.
The voltage to the external switch needs to be about 7.5vdc and from 9-12vdc at the 555 output. I'm powering it with a 12.4vdc power supply. I tried the smaller npn's 2n3904 & 2n2222, but didn't seem to switch. I'll try a TIP 31 and see if that helps. I've tried using the resistors listed, but so far it isn't working. I'll keep trying. The circuit I posted at the beginning is the schematic I started with and the only thing that I needed to do differently was have the switch go to ground like the external switch ScottWang posted. ThanksWhat do you trying to connects the 8vdc to the switch?
If you could upload the schematic then it might help.
The switch (Scott Wang cct.) connects across the base and emitter of the transistor. It does not need, and shouldn't have, any other voltage applied to it. When the switch is open, the voltage across it will be the base/emitter voltage of the transistor - about 0.7V,I'll be running 12vdc through the circuit and probably 8vdc to the switch.
I don't really understand what does it means?I really need 7.5 vdc running to the switch.
If you have a multimeter can you measure the base and collector voltages of the transistor when the switch is closed and when it is open, please.
(Using either 2N2222 or 2N3904)