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Velleman 12 key common output confusion

DickFreed

Aug 6, 2021
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I have this keypad for a project I’m working on, and it’s not behaving as I would expect. If I hook 5v up to pin 1, I’m getting 3.1v from pin 3, the “*” key, without even pressing the keypad. Also getting full voltage out from pin 2, the “/“ which is a whole other question because I have no idea what “/“ relates to.

i checked all my header pins to make sure I hadn’t shorted any of them while soldering it on. I tried uploading pic using ‘upload file’ but it won’t work. https://imgur.com/a/2plRXuj. I completely removed the keypad from rest of project to isolate it. It demonstrates same behavior in and out.
 

DickFreed

Aug 6, 2021
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The only load was the meter I was testing with. Please explain as I am pretty new to this. I figured a keypad was basically a bunch of button switches and acted the same.
 

bertus

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Nov 8, 2019
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Hello,

What is your meter?
You could also measure the resistance of the switches, using the resistance range of the meter.
As for the / , it is not used.
On the velleman site the box for pin 2 is slashed.

Bertus
 

DickFreed

Aug 6, 2021
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The only load was the meter I was testing with. Please explain as I am pretty new to this. I figured a keypad was basically a bunch of button switches and acted the same.

edit: i see contact resistance applies to when keypad is closed. What does that have to do with getting voltage on a button that I’m not pushing? Are you hinting that I should check the resistance and if it’s around 200 ohm that the switch must not be holding open.
 

DickFreed

Aug 6, 2021
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Hello,

What is your meter?
You could also measure the resistance of the switches, using the resistance range of the meter.
As for the / , it is not used.
On the velleman site the box for pin 2 is slashed.

Bertus
Resistance is about 5 megaohm when open between pin 1 and 3. 8 ohms when closed.
https://imgur.com/a/9Rr1U4e meter is old radio shack 22-163
 

bertus

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Nov 8, 2019
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Hello,

That shows that the switch is working.
You could test the other switches the same way.

Bertus
 

DickFreed

Aug 6, 2021
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Ok, thanks. I guess I’m confused, but those voltages on the pins that I wouldn’t expect to be there are triggering my gates without even pressing the buttons. I’m glad the keypad is at least eliminated from the equation though.
https://imgur.com/a/LloqWK6
 

Martaine2005

May 12, 2015
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What does that have to do with getting voltage on a button that I’m not pushing?
That would suggest the button is de-pressed, possibly faulty or sticky.
I drew a schematic demonstrating the way I’m looking at it
Your schematic has all switches in parallel which would achieve nothing. One on or all on will give the same reading.
Both of your meter probes are connected to the negative terminal.
Finally, connecting switches as you have drawn, will simply short the battery. You will directly connect positive and negative together.
Pin 2 is nothing as already stated.

Martin
 

bertus

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Hello,

The schematic you posted in post #8 looks like a code lock:
code lock.jpeg
A fixed order of numbers needs to be entered to activate the lock.

Bertus
 

DickFreed

Aug 6, 2021
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“A fixed order of numbers needs to be entered to activate the lock.”

that’s exactly what it is. I got it working. https://imgur.com/a/hYbRmMm.
Green led is just an indicator for that it’s getting power. Must hold in “*” to provide that power. The blue led at the bottom fed by pin 3 of the 555 lights up when I enter the correct 3 digit pin. What’s not in the video is that if I’m not even giving the chips power by pressing “*” and just press any random key, the green led flickers at about half intensity.
 
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