I want to design a smaller keypad than the one that comes with the qwiic keypad. I opened the keypad up and it looks like there are resistors in the board.
Does anybody have a diagram of the 3 resistors used in the keypad circuit?
I would like to use the qwiic circuit board and just replace it on my smaller keypad.
Any help would be appreciated.
Thank you,
Steve
I would not expect any resistors in the keypad itself. Are you sure they aren’t jumpers (0-ohm resistors) to let them use a single-sided board? The keypad schematic at https://cdn.sparkfun.com/assets/7/e/f/6 … keypad.pdf doesn’t show any resistors
/mike
They definitely have resistance in the jumpers.
Please see view of opened keypad https://www.openop.com/keypad.png
I put a ohms meter between the connector on both sides of the connector and it shows some resistance.
Also on the diagram you referred it says at the bottom that a keypress will have 10 to 150 ohms resistance.
From the top of the board (1st connector horizontal) … I measured 75 ohms , 2nd vertical connector 100 ohms and 50 ohms for the 3rd connector vertical connector towards the bottom going to pin 6.
Those are just carbon links to jump over traces. Since they are carbon (cheap to produce) there’s a bit of resistance in them but it’s low enough to be considered a non issue by a connected microcontroller.
The resistance you see when buttons are pushed is also a result of the keys having a carbon rubber pad on them that makes contact with the PCB traces. Zero ohms would be ideal but there is some resistance in carbon rubber and that’s what you’re seeing. The harder you press on the key, the lower the resistance is going to be but again, a microcontroller isn’t really going to care, it’s just looking for a change from no current flowing to some current flowing. Even if there is some resistance it doesn’t really matter.
When you design your smaller keypad, don’t include any resistors and it should work just fine.
