How to avoid jitters when reading a output voltage?

[khanna_gunjan]

How do i avoid Jitters

Hello,

In one of my application, i am trying to read a Output Voltage of a reed contact in the microcontroller and i am using an opto-coupler for the purpose. The problem is that before the contact is properly closed, there is these jitters there ( with jitters i mean closing and opening of the contact at a very fast rate, before it finally stablizes).

Can anyone suggest me a simple solution to avoid these jitters with few components. Also, i would like to mention that the output of the opto-copler is then read by the microcontroller and which can only generate an interuppt when it sees the falling edge of the signal and i tried to use an RC circuit at the output of the opto-coupler .. but with the slow charging and discharge time the controller is not able to detect the falling edge of the signal..

Please suggest. thanks

Gunjan

 

[tronix]

Re: How do i avoid Jitters

To avoid jitters u can follow either of the two approaches
1.h/w approach : use nand latch as input stage(google to get ckt)
2.s/w approach : give some time delay for reading of switch after sensing first change of state

 

[khanna_gunjan]

Re: How do i avoid Jitters

I am now trying with connecting a cmos Inverter (with a change in input reference from high to low) in the input side .. as the delay time for this inverter will be a around 200 ns seconds .. i think it will help..

any suggestions on this.. ??

 

[tronix]

Re: How do i avoid Jitters

Iam not sure that u hv got d solution.
Using a time delay is Software Solution and what this mean is that after sensing first change of state microcomputer(or device which is used to read switch) should wait for some time > bounce time and then take the reading again which if found different from the previous reading indicate false switching and a valid transition otherwise.

If u want to hv a h/w approach go for nand in input.
Google for more details

 

[khanna_gunjan]

Re: How do i avoid Jitters

Iam not sure that u hv got d solution.
Using a time delay is Software Solution and what this mean is that after sensing first change of state microcomputer(or device which is used to read switch) should wait for some time > bounce time and then take the reading again which if found different from the previous reading indicate false switching and a valid transition otherwise.

Thanks.. this really helped

 

[haytham]

Re: How do i avoid Jitters

You need monosatble circuit
it is simple

 

[safwatonline]

How do i avoid Jitters

i think this is called de-bouncing and it originally found for push buttons as they bounce , there r several soultions i dont know if they r applicable to ur optocoupler but here they r anyway
https://www.elexp.com/t_bounc.htm

p.s. a simple delay loop seems to be the right and simple appraoch.