Circuit design for 15 minute delay

Thread Starter

gebseng

Joined Nov 24, 2017
35
Hey everyone,

what is the name for a circuit design that closes a contact for a second on the push of a button, but then disables this button for fifteen minutes? Could you steer me towards a design that can do that?
The current I have to switch is DC below 12V and in the Milliwatt range.

thanks, geb
 

dl324

Joined Mar 30, 2015
12,873
what is the name for a circuit design that closes a contact for a second on the push of a button, but then disables this button for fifteen minutes? Could you steer me towards a design that can do that?
You're going to need two timers. One for the one second contact close and a second to disable the 1 second timer for 15 minutes.

What is being used to trigger the one second timer? What accuracy do you need for the 15 minute interval? That's a bit long for a 555 timer unless you use a CMOS version.
 

AnalogKid

Joined Aug 1, 2013
9,261
15 minutes is a looooong time for a simple R-C timer. Better to use a monostable circuit for the 1-second output pulse that then inhibits itself with gating or by setting a flipflop, and an oscillator/counter chip for the 15 minute delay before it resets/ungates the switch circuit. Probably two chips total. Some variation of this probably is where dl and Wally are headed.

Someone will bring up a PIC, Atmel, or some other small microcontroller. True, nothing will be smaller or cheaper than an 8-pin uC - after you develop the firmware to do the task.

And, there are programmable timers on ebay for cheap.

ak
 

dendad

Joined Feb 20, 2016
3,840
I would use an Arduino. Ebay or similar costs are well under $10. And this would be a good project to learn on.
It will be accurate and easily modified to suit later if needed.
 

Tonyr1084

Joined Sep 24, 2015
6,000
I'm thinking "Monostable, non-retriggerable (MNR)" or "One Shot (OS)" circuit.

With the MNR or the OS, once the timing sequence is triggered it can not be retriggered until the time period has timed out. For instance, and what I think the TS wants, you push the button and the MNR switches on (which can be used to switch a circuit on or off). The button can not be pressed again until the time period times out. You can push the button all you like but it won't change the timing of the circuit. That is to say, you push the button and start the 15 minute period. During that time you can push that button thousands of times but it doesn't change the 15 minute period. Once the 15 minutes has been met you can again trigger the timer.

There are other circuits such as a "Monostable, RETRIGGERABLE" multivibrator circuit where you can push the button once and set off the 15 minute period. Come back after (oh - lets say) 10 minutes and push the button again. From the second press of the button you reset the timer for an additional 15 minutes, thus, the circuit would remain active for 25 minutes (assuming you pushed the button a second time at the 10 minute mark).
 

Tonyr1084

Joined Sep 24, 2015
6,000
Here's one I found on the internet. When you pulse the input U1 changes its output to a LOW causing CtRt to trigger U2. U2 holds U1 output low until the time period expires; then U2 goes low, allowing U1 to reset. During that period all other input pulses (button presses) are ignored.
1606317149927.png

[edit] link removed due to reported trojan threats. [end edit]
 
Last edited:

Marley

Joined Apr 4, 2016
411
Someone will bring up a PIC, Atmel, or some other small microcontroller. True, nothing will be smaller or cheaper than an 8-pin uC - after you develop the firmware to do the task.
That would be me.
With micro-controller - one 8-pin IC. Hardly any other components. Time millisecond accurate.
With R/C timers and CMOS logic - lots of ICs. Time accurate to about 10% at best (although you could adjust with a couple of variable resistors).

The downside: you need a programmer (cheap), programming environment (free) and a bit of programming knowledge (time).
I would use an Atmel (now Microchip) ATTINY device.
 

ElectricSpidey

Joined Dec 2, 2017
1,681
Another downside, take it from me...is the need for a 5 or 3.3 volt regulator if the voltage you have available is above that, and your micro board doesn't have one.

There are others such as micros don't like being in an environment with inductive loads...but...enough.
 

Thread Starter

gebseng

Joined Nov 24, 2017
35
Here's one I found on the internet. When you pulse the input U1 changes its output to a LOW causing CtRt to trigger U2. U2 holds U1 output low until the time period expires; then U2 goes low, allowing U1 to reset. During that period all other input pulses (button presses) are ignored.
View attachment 223363

Monostable non retriggerable There are many more options.
Bingo, thank you so much!
 

Tonyr1084

Joined Sep 24, 2015
6,000
The circuit in #12...where are you going to acquire the one second pulse from?

Also Tony, when I clicked on that link I got a trojan warning.
I've clicked on both sites without any warnings. Wonder why my computer isn't seeing that. I have malware protection as well as protection against trojan's. Let me know if it happens again and I'll edit out the links.
 
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