Hold Down Switch

[maxmcp]

Hi,
I am trying to work out a way of having a switch that has to be held down for a period of time (say 1 second) before it switches on the circuit so that brief touches on the button are ignored. I was wondering if there is a way to use the timing provided by a 555 IC as I have some of these to hand. Alternatively could I use a capacitior and a transistor to detect if it has charged beyond a certain amount (using the charging time to provide the function)? Has anyone used a circuit like this?
Thanks,
Max

 

[BrownOut]

Sure, just connect the trigger pin of the 555 to an RC circuit that is switched by your pushbutton. R&C should be chosen to provide 2/3VCC after charging for 1 second.

 

[maxmcp]

Thanks for the speedy reply! I'll give it a go!

 

[BrownOut]

You can either charge or discharge the cap, depending on how you connect it. If you discharge it, the output of your timer will go high after the time delay. If you charge it, then the output will go low. The timer should feed another latch or something, as the charge will eventually leak out.

 

[BrownOut]

The timer should feed another latch or something, as the charge will eventually leak out.

Never mind that part. The timer can be configured to stay on even after the charge has leaked away.

 

[maxmcp]

Hi, is it possible to trigger the circuit so that the output goes high after the capacitor on the trigger circuit charges? Otherwise the circuit would need to be on all the time to detect the drop in voltage. Ideally I wanted to use this as an on switch so would like the circuit to be powered on at the same time as pressing the button (or even doing away with the button and just having the circuit provide a high output 1 or 2 seconds after the circuit has been provided with power)
Thanks