Connect the switch to the reset pin. The reset pin discharges the cap if pin 6 is tied to 7. Transistor not needed.

The reset pin overrides the trigger pin.

That's not how the circuit was originally intended. The circuit was designed to monitor a closed switch. As long as the switch is closed the output of the 555 remains high or alarm OFF. If the switch is open for a period longer then the timing cycle then output low, alarm ON until the switch is closed again.
SG

 

Latest iteration. C1 upped to 68u to slow down charging and 1u pin4 to GND for startup suppression.

 

That's not how the circuit was originally intended. The circuit was designed to monitor a closed switch. As long as the switch is closed the output of the 555 remains high or alarm OFF. If the switch is open for a period longer then the timing cycle then output low, alarm ON until the switch is closed again.
SG

Or if it is open on power up you have x time to close it before alarm is triggered.

 

Or if it is open on power up you have x time to close it before alarm is triggered.

Not true if the circuit is working properly.
The breadboard looks setup properly. The switch appears closed to ground.
Is the circuit working?
SG

 

No it isn't, and Mins described it as I stated, starting sw1 open and closing before x timed alarm.
Working on 555 test ckt. My notes for monostable show pin6 and 7 jumpered?

 

So what does it do when powered up?
SG

 

No it isn't, and Mins described it as I stated, starting sw1 open and closing before x timed alarm.
Working on 555 test ckt. My notes for monostable show pin6 and 7 jumpered?

First off Mims is wrong in this particular circuit. This is not the first time I have seen his circuits drawn incorrectly.
Two mistakes: pin6 connected to pin7 and omitting a .1uf cap from pin2 to ground.
Your diagram of a 555 monstable is also incorrect.
SG

 

I'm not surprised about Mims since I had another of his circuits that we wrong, When powered LED immediately lights and 0V on pin6 with sw1 closed. And I added .1uF to pin2 to GND. Will work on my notes later to build chip test circuit.

 

I'm not surprised about Mims since I had another of his circuits that we wrong, When powered LED immediately lights and 0V on pin6 with sw1 closed. And I added .1uF to pin2 to GND. Will work on my notes later to build chip test circuit.

Nevermind how Mims version works....how do YOU want it to work?

eT

 

That's not how the circuit was originally intended. The circuit was designed to monitor a closed switch. As long as the switch is closed the output of the 555 remains high or alarm OFF. If the switch is open for a period longer then the timing cycle then output low, alarm ON until the switch is closed again.
SG

I get it sghioto...I was just describing how the 555 works..

eT

 

Nevermind how Mims version works....how do YOU want it to work?

eT

The idea was to intervene and prevent an event failure alarm. That has morphed into a 555 timer issue since was using timer to delay the failure alarm.

 

SamR you must have a bad chip and this would not be the first time after that incident with the LM311.
I bread boarded the circuit and it works as described in post #21.
SG

 

Working on test circuit now, back in a bit...

 

I had 7 NE555P and 1 was bad. I had already swapped 1 timer and things got confusing testing so not sure which one was on the board. Put good timer on board and OV at pin6 and 4.45V on pin OUT.

The monostable test calculated for 5.12 seconds which it did.

 

I had 7 NE555P and 1 was bad. Put good timer on board and OV at pin6 and 4.45V on pin OUT.

Have you tried the circuit in post #8 now that you know the chips are good?
SG

 

Current iteration and original Mims sketch. Note that Mims had this for a 9V battery supply and I am using 5V bench PSU. I replaced the noisy active buzzer w/ a LED. Yes, this is the msg#8 config.

 

Measured Voltage in RED

 

Voltage in RED
View attachment 173241

Those voltages are correct but with the switch closed.
SG

 

I removed the switch and get the same.

 

I removed the switch and get the same.

What voltages are the same? Not pin2.
SG