The switch in this schematic connects negative supply to the trigger and activates the timing cycle. I want to know how, without changing the initial circuit, can I use a transistor to implement switch that triggers from positive supply instead.
Any help would be greatly appreciated as per usual!

 

Add a transistor wired as an inverter. Putting a HIGH on the base resistor will cause it to turn on and give a LOW on the collector. When the base resistor is at a LOW logic level, the collector will be at a HIGH logic level.

 

You mean like a not gate?
I tried this though and it didnt work before. Ill give it another shot, will be back with results.

 

You mean like a not gate?
I tried this though and it didnt work before. Ill give it another shot, will be back with results.

Yes, an inverter. I used a transistor because you said mentioned using a transistor.

 

The voltage at the node between r1 and the collector in the not gate, reads 6v upon button press, despite the led turning off. As a result the trigger does not go low

 

The voltage at the node between r1 and the collector in the not gate, reads 6v upon button press, despite the led turning off. As a result the trigger does not go low

What are you using for the not gate? Did you use the simple 2N3904 circuit, or some inverter IC? How exactly did you wire it into your 555 schematic?

What LED are you referring to? There is none shown in your schematic.

It's hard to help troubleshoot a circuit without knowing what you've got.

 

The voltage at the node between r1 and the collector in the not gate, reads 6v upon button press, despite the led turning off. As a result the trigger does not go low

Are you referring to the component designators on the schematic I posted? If so, that does nothing to the trigger input.

 

Add a transistor wired as an inverter. Putting a HIGH on the base resistor will cause it to turn on and give a LOW on the collector. When the base resistor is at a LOW logic level, the collector will be at a HIGH logic level.

View attachment 202598

yes , but perhaps to pin 2 (\(=\overline{SET}\)) while the pin 4 (\(=\overline{RESET}\))

 

Add a transistor wired as an inverter. Putting a HIGH on the base resistor will cause it to turn on and give a LOW on the collector. When the base resistor is at a LOW logic level, the collector will be at a HIGH logic level.

View attachment 202598

SOLVED IT!!!!!
Nether of us seemed to notice that we were running r1 to 5v+ rather than to pin 4!!!
It works now!!!! New schematic to follow!

 

Special thanks goes out to dl324, ebeowulf17 and anyone else who help work out this problem. You guys are champs.


Thanks guys, this is actually a pretty great little circuit.