Author Topic: Proper 4x4 Keypad Operating Behavior?  (Read 1081 times)

0 Members and 1 Guest are viewing this topic.

Offline t1dTopic starter

  • Super Contributor
  • ***
  • Posts: 1255
  • Country: us
Proper 4x4 Keypad Operating Behavior?
« on: September 18, 2018, 10:20:16 am »
I have these two keypads. They have what I consider to be an odd behavior. For both units, when tested with a DMM, some buttons will test correctly, for continuity. Other buttons do not, but they do register resistance, meaning something is getting through.

I think the button switch contacts are some type of soft pad, which closes the circuit, on the bare traces, on the PCB.

So, should they all register continuity, as I would expect? Or, due to the nature of the contact pad, resistance is typical. If resistance is typical, how is this type keypad employed in a circuit, generally speaking?

https://www.ebay.com/itm/16-4x4-Buttons-Keyboard-Keypad-Key-Matrix-PIC-AVR-Stamp/370528911434?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2748.l2649

https://www.ebay.com/itm/4-x-4-Matrix-Array-16-Keys-4-4-Switch-Keypad-Keyboard-Module/150655776761?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2748.l2649

 

Offline Benta

  • Super Contributor
  • ***
  • Posts: 6420
  • Country: de
Re: Proper 4x4 Keypad Operating Behavior?
« Reply #1 on: September 18, 2018, 11:52:08 am »
Those keyboards usually have little rubber "nipples" under the keys. On the underside there is a soft conductive plastic part that closes the connection directly on the PCB.
Conductive plastic has a certain resistance, so it's not like a metal to metal connection.

Keyboard decoding is not an issue, there's no reason for low resistance.

 

Offline PTR_1275

  • Frequent Contributor
  • **
  • Posts: 561
  • Country: au
Re: Proper 4x4 Keypad Operating Behavior?
« Reply #2 on: September 18, 2018, 11:52:35 am »
I’d say they might be borderline to what your meter counts as continuity or not. What is the resistance of them?
 

Offline Richard Crowley

  • Super Contributor
  • ***
  • Posts: 4321
  • Country: us
  • KJ7YLK
Re: Proper 4x4 Keypad Operating Behavior?
« Reply #3 on: September 18, 2018, 12:13:17 pm »
That is normal. Because those switches use conductive rubber/plastic buttons you will never see the very low resistance of a traditional metal-to-metal switch. 

That kind of switch is typically used with a micro-controller to decode which switch is activated. Because very low voltage and current is used, a hard metal-to-metal, low-resistance contact is not required. 

Because the bottom part of those switches are a conventional PC board, and the top (plastic button) part is pretty standardized, it is relatively inexpensive to make very customized configurations for user interfaces for everything from automobiles to toys.
 

Offline Rerouter

  • Super Contributor
  • ***
  • Posts: 4705
  • Country: au
  • Question Everything... Except This Statement
Re: Proper 4x4 Keypad Operating Behavior?
« Reply #4 on: September 18, 2018, 12:24:16 pm »
It also comes down to the exact type of button, some will use metal pop domes, those are a hard short, but they cost more so they are rarely used (I like the feedback so Always pick them for my stuff) the rubber press pads generally seem to be about 100-1K resistance, they are generally graphite embedded or similar, so they make a conductor, just not a good one.
 

Offline t1dTopic starter

  • Super Contributor
  • ***
  • Posts: 1255
  • Country: us
Re: Proper 4x4 Keypad Operating Behavior?
« Reply #5 on: September 18, 2018, 01:04:30 pm »
The resistance was very low, AIR...

All very great answers. Thanks, to each of you!
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf