Hi,
I'm trying to design a delay circuit to trigger a 555.
The effect I want is similar to a switch-on delay circuit which I'd normally do with a RC series and a switch (normally closed) across the capacitor. This gives exactly the output I want:
- when the switch is first opened the capacitor begins to charge until it reaches the threshold voltage and pushes the trigger up/down to the required voltage, but
- if it's closed again before the threshold voltage is reached, it discharges the capacitor and the delay is reset [it's this behaviour that I really need].
The problem is that I need it to work with a normally open push button
- ie closing the switch triggers the 555 after a delay
- if the button is released before the delay time, do nothing, and reset the delay.
It's years since I've done any serious electronics and it's taxing my brain - it's the second part of the requirement that I'm struggling with.
I'm just using the 555 as a Schmitt trigger, btw.
Grateful for any help...
I'm trying to design a delay circuit to trigger a 555.
The effect I want is similar to a switch-on delay circuit which I'd normally do with a RC series and a switch (normally closed) across the capacitor. This gives exactly the output I want:
- when the switch is first opened the capacitor begins to charge until it reaches the threshold voltage and pushes the trigger up/down to the required voltage, but
- if it's closed again before the threshold voltage is reached, it discharges the capacitor and the delay is reset [it's this behaviour that I really need].
The problem is that I need it to work with a normally open push button
- ie closing the switch triggers the 555 after a delay
- if the button is released before the delay time, do nothing, and reset the delay.
It's years since I've done any serious electronics and it's taxing my brain - it's the second part of the requirement that I'm struggling with.
I'm just using the 555 as a Schmitt trigger, btw.
Grateful for any help...
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