Timed Switch

[XantorAmnobius]

Is it possible to make a timed switch with analog circuits?

In other words. I have to press a switch for longer than... let's say one second for the circuit to trigger. Basically I want to make something that cannot be accidently pressed - you need to press and hold it down for a x amount of time. Almost like the switch on a computer.

I have tried a 555 timer, but I'm missing something.

 

[prprog]

Is it possible to make a timed switch with analog circuits?

In other words. I have to press a switch for longer than... let's say one second for the circuit to trigger. Basically I want to make something that cannot be accidently pressed - you need to press and hold it down for a x amount of time. Almost like the switch on a computer.

I have tried a 555 timer, but I'm missing something.

Connect the input to a capacitor/resistor --> this to a comparator. Set the comparator to trigger at a certain voltage level. The time to fully charge the cap (...well to a certain percentage) will determine the trigger.Connect the comparator to an analog switch (4066 chip). if you press it longer enough (time) the switch will be activated.

 

[Hero999]

Think about it.

If you use an AC coupling capacitor, the 555 will output a 1 second pulse then go low but the input and the input to the trigger will remain low.

You want the circuit to trigger when the trigger to the 555 is low and the trigger pin is low.

You need a NOR gate with one input on the switch and the other on the outpu of the 555.

 

[XantorAmnobius]

New to this...

Could you possibly give an example - schematic please?

 

[Hero999]

Have a go at drawing it and I'll be happy to help.

 

[XantorAmnobius]

New to this...

I'm fairly new to this - I know how some of the components work. Like the 555, capacitors, transistors, thyristors, coils and some other.

What exactly do you mean with an AC coupling capacitor.
A NOR gate I know how it works.

0 - 0 = 1
1 - 0 = 0
0 - 1 = 0
1 - 1 = 0

That is the basic function for the NOR Gate.
I've tried searching for AC Coupling examples - Googled it - Could not find good explanation.

Help please?

 

[ericgibbs]

I'm fairly new to this - I know how some of the components work. Like the 555, capacitors, transistors, thyristors, coils and some other.

What exactly do you mean with an AC coupling capacitor.
A NOR gate I know how it works.

0 - 0 = 1
1 - 0 = 0
0 - 1 = 0
1 - 1 = 0

That is the basic function for the NOR Gate.
I've tried searching for AC Coupling examples - Googled it - Could not find good explanation.

Help please?

hi,

Have a look thru these links:



https://www.unitechelectronics.com/NE-555.htm

https://www.electronicsteacher.com/tutorial/

https://en.wikipedia.org/wiki/Capacitive_coupling

 

[Hero999]

See page 7 of the datasheet.
https://www.electro-tech-online.com/custompdfs/2008/08/NE_SA_SE555_C_2.pdf

 

[Willbe]

I have to press a switch for longer than... let's say one second for the circuit to trigger.

Will a switch debouncer work?

 

[Hero999]

No because if the pulse from the switch lasts longer than the time delay the 555 will keep pin 3 as long as the trigger is still low.

The AC coupling capacitor provides a negative pulse lasting for no longer than 2RC (to 86.5%), the 555 triggers and that's it.