555 input desense

[jberry20]

I have a small project using a 555 timer in a monostable configuration
However, I need an idea on how to block or desense the input signal for a second or so after the timer returns to baseline state
My output (a solenoid) generates a transient upon closing that immediately retriggers the input (bad), so I need to make the input line deaf for a brief time while everything settles down after a cycle.
I think I just need to hold the input high for a sec, but would putting a small cap between output and input lines do it?

Thanks

 

[Les Jones]

Welcome to the forum. It may be better to tackle the problem by trying to stop the transient from triggering the 555. Can you post an EXACT schematic, the resistance of the solenoid and the voltage and current capability of the power source.

Les.

 

[KeepItSimpleStupid]

Do you have a reverse-biased diode across the solenoid? At the solenoid would be best if long leads are involved.

 

[jberry20]

For KISS, the solenoid is diode-protected - the transient of issue is a pressure spike from the solenoid closing.
The input is a very sensitive pressure transducer
So, the unwanted feedback is non-electrical

 

[KeepItSimpleStupid]

The 55 is easily triggered.

I found these https://www.linear.com/docs/30203 (Timerblox) not to long ago. I haven't had a need for any yet.

 

[alec_t]

You could use a second 555 to prevent the first re-triggering.

 

[jberry20]

They make dual 555s, so you get the vote for most helpful member
Any easier way to have output keep input high for a sec after cycle is over?

 

[AnalogKid]

You can use the trailing edge of the 555 output to drive an R-C network to the reset pin. This will hold off responding to a trigger input until the reset pin is released. Capacitor from pin 3 to pin 4, resistor from pin 4 to pin 8

ak

 

[jberry20]

Perfect