Thank you for reading my question, I hope to learn a new way to solve my problem. I don't expect anyone to design a cicuit etc as hopefully I can do that myself, just some pointers at possible components to consider.

I have a device that has a built in electronic timer, after a while an LED lights up and I have to press a button to continue using the device.

The button is just a normally open contact switch.

My first thought is to use an arduino and either directly from the LED or via an opto-isolator monitor the LED, when it lights up use the arduino to momentarily close the switch thus resetting the internal timer.

The circuit board itself has regulated 12v and 5v available but since it is mains powered I can power from pretty much anything.

Perhaps there are some other IC's or transistor etc I could use on some bread-board to trigger the switch instead of having an arduino.

I'm not very familiar with how to do this so any pointers at what to look at would be greatly appreciated.

Many thanks.

  • \$\begingroup\$ Is it possible to reset the timer in the device by pressing the switch before the LED comes on? \$\endgroup\$ – Michael Karas Jan 14 '19 at 9:32
  • \$\begingroup\$ Hey thank you for the reply. unfortuantly not. However, I have discovered the MAX4644 small analogue switch IC that I think I can use as a one chip solution! I am just checking over the data-sheet before ordering one but since I have the LED light I can use that as the control signal to trigger the IC, as the LED goes out after the reset the switch in the chip will also open too. If you have any other suggestions though i'd be interested to hear them. \$\endgroup\$ – West Jan 14 '19 at 9:35

You could always have the output for LED go through an RC delay and an XOR gate.
You can then use this output signal and feed it directly to where the button is fitted as it would simulate a button press of 'x' amount of time.


simulate this circuit – Schematic created using CircuitLab

I've also done a simulation to show you what the effects would be, for a longer/shorter pulse duration you would need to play around with the value of the resistor and capacitor but only there is lots of help for RC calculations, google "RC Calculator"

Simulation Link

Simulation Screenshot

  • \$\begingroup\$ Hey thank you for your detailed reply, this is an interesting way to solve the issue too. The RC delay isn't necessary for the circuit im working on at the moment but is definatly something ill build and play with as it might be useful in the future. Thanks again. \$\endgroup\$ – West Jan 14 '19 at 13:45

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