555delayintegrated-circuittimer
In my design, say there are 2 pins A and B.
Now I want to implement circuit in such a way that B is initially high , but when A goes low, after 12 seconds B will go low for short duration and again will become 1.
Is there any circuit which I can implement.
I tried below Monostable multivibrator as timer using IC555, but issue is that initially B is low as per configuration.
Required signals as below:
Can someone help me and suggest? Thanks in advance.
It's called a non-retriggerable monostable. Here's one that isn't a 555 just to show that there is life beyond that ubiquitous animal: -
The 555 timer is fairly adept at most things in the timer bracket so maybe try searching for "555 non-retriggerable monostable". Here's a circuit but I'm no expert on 555s
You can't use the main timing resistor and capacitor to generate your trigger signal. As you discovered, this is exactly equivalent to the astable configuration.
Instead, you need to provide a separate resistor (to Vcc) and capacitor (to ground) for the Trigger pin. The time constant for this pair should be short relative to the main timing period, but long relative to the risetime of the power supply.
These components will hold the trigger low while the chip powers up, but then allow it to go high a short time later. Once the timer has timed out, the main timing capacitor will be discharged, but the trigger capacitor will not.
Best Answer
You could use a Schmitt-Trigger with an RC-LP on it's input and two different resistors for charging and discharging. If Input A goes low, C1 will be discharged via R1. Use a time constant to create 12s delay till the Schmitt-Trigger goes low. R2 determines the time it takes the output to go high again, after A went high.
Alternatively, you could obviously use a small µC like an ATtiny. This would give you a lot more flexibility.