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Another push button bypass

msratauls

New Member
hello there,

I am trying to bypass a push button switch on my dehydrator unit.

The dehydrator when plugged in does not power up straight away. It has a push-button on the front that you have to press to get it to work. If you turn if off at the main and turn it on again, you have to press the front button again to power the device on. The button is essentially push button with 4 terminals.16114654753417101080578032693445.jpg16114655205801073476925367859805.jpgThere are 4 terminals on the push button. Shorting of any 2 terminals achieves the functionality desired ie plugging the power switches on the circuit but by doing this rest of the buttons on the dehydrator like temp contr stop working. Im
Thanks
 

Visitor

Well-Known Member
The switch is momentary contact and sends a signal to a microcontroller to turn the power on and off.

Shorting out the switch so you don't have to press it, presumably to turn it on/off by an external switch may or may not work, depending on the microcontroller code. You can test if shorting out the switch will work. Unplug the unit from the wall. While pressing the switch, plug it back in. Does the unit start and operate OK? Continue pressing the switch. Is the unit operating properly, without any glitches of any kind? If so, shorting the switch should work.

If any glitches occur, like shutting off while you're holding the switch or failing to control operation properly, you're out of luck.
 

Visitor

Well-Known Member
If holding the switch closed works, you can short the pins together on either side of the switch where the pins come out. In this diagram, shorting 1 & 3 or 2 & 4 will work.


Screenshot_20210124-030144_Edge.jpg
 

msratauls

New Member
Thanks for the reply,

I tried that. The unit continues to work at baseline set parameters as it would if i switch it on normally (normally if i switch it on it sets itself at 122 degree for 10 hrs). It does not turn off. However i am unable to press any other buttons on it including changing the temperature to higher values or change the timer. All other buttons rendered useless.

Also shorting the terminals momentarily toggles the power on and off as well. As per your diagram something has to be there to keep the circuit closed even if i let go the switch.

Worth mention in another similar thread i read it said shorting the terminals using capacitor and resistor in series. Would it work here?

Regards and thanks for the help
 
Last edited:

Visitor

Well-Known Member
The switch controls an input to a microcontroller. It's a momentary contact that triggers the microcontroller to do something. In this case, turn the dehydrator on if it's off or off if it's on.

Looks like shorting the switch inhibits the microcontroller from reading the other switches.

So, afraid you're out of luck turning it on remotely with any easy solution.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
A simple solution is a micro-controller (such as an 8 pin PIC), programmed to close either a reed relay or FET switch briefly after a short delay. Failing that, a couple of 555 timers can be utilised to do the same thing, but it's considerably more complicated.

I modified a number of old cam-corders many years ago using 555's in this way, so as to use them as high quality security cameras.
 

msratauls

New Member
Worth mention in another similar thread i read it said shorting the terminals using capacitor and resistor in series. Would it work here?

Regards and thanks for the help
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Worth mention in another similar thread i read it said shorting the terminals using capacitor and resistor in series. Would it work here?

Regards and thanks for the help
In my experience with the cam-corders you had to add a delay before shorting the contacts out, so you couldn't just use a capacitor.
 

msratauls

New Member
Instead of microcontroller is it possible to use arduino/esp controlled relay to momentarity close the circuit across the terminals so that on off effect be achieved.
 

msratauls

New Member
My projects involves a humidity controlled (BME280--> esp8266 -->Relay --> Dehydrator) circuit relay to energize the NO relay so that the dehydrator switches on and off based on humidity values. I already have the setup upto the relay control except now I discovered the problem comes to the push button the dehydrator above. Any ideas how to power the relay to achieve the simulation of "button press" .
 

msratauls

New Member
Problem solved.
I connected 2 terminals on the push switch using capacitor and resistor in series. I was not waiting for 5-10 sec after the power off so the switch seemed to stuck but after wait it resets as expected. All the functions work while shorting with cap and resistor. I wonder if the size of the capacitor and resistor has to do anything with the time for discharge after turn off.

Thanks guys for your help and thanks to BF9000 for this trick suggested in other thread
 

gophert

Well-Known Member
Most Helpful Member
Problem solved.
I connected 2 terminals on the push switch using capacitor and resistor in series. I was not waiting for 5-10 sec after the power off so the switch seemed to stuck but after wait it resets as expected. All the functions work while shorting with cap and resistor. I wonder if the size of the capacitor and resistor has to do anything with the time for discharge after turn off.

Thanks guys for your help and thanks to BF9000 for this trick suggested in other thread
the discharge time depends on the rest of the circuitry but you'll have to check that it actually does discharge after the first charge. If it works, who cares how long it takes to discharge as long as it discharges by the time you want to use the dehydrator again.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
yep, two f the terminals are just feet and it's a simple SPST switch.

I tend to use an OPTO_FET tointerface with buttons. Usually, you don;t have to have a near zero ohm short for it to work. 200 ohms might work fine. There are also OPTOMOS relays. You only need 1 mA to turn them on and some have low contact resistance,
 

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