Hooking up sensors to simulate numpad key press

Hi, I have a project that I want to try doing without an Arduino.

I want to use common 3 pin sensors (GND, VCC, SIG) such as touch sensors and knock sensors to simulate numpad key presses which I can plug via USB into my computer.

I popped open one of my old USB numpads and took out the board, I figured out the combinations that gives me the desired keys. The keyboard basically has a 5V, GND, and bunch of pins that if I touch different pins together I get different keys typed into my computer.

I've tried hooking up a pair of the key pins to push buttons and it works perfectly.

However what I want is to hook up certain keys to sensor switches.

I don't have any experience with keyboards so I just hooked up as follow: Numpad 5V ---> Sensor 5V Numpad GND ---> Sensor GND Numpad pin 11 ---> Sensor GND Numpad pin 7 ----> Sensor SIG

(touching pin 11 and pin 7 together types the number "7" on my computer)

Well in the end it didn't work, but when I started pulling out 1 of the wires, it starts typing the key that I wanted to be typed when triggered, but instead of just typing when i trigger it, it just keeps typing it endlessly no matter what.

Is there a way that I could get this to event work at all?

Keypads usually work on a grid system. On a 4 x 4 keypad, there are 4 data lines connected to the rows and another 4 connected to the columns.

To read the keyboard, the processor applies a signal to one row at a time and reads each column sequentially to see if the signal appears. If the signal appears, the button on the intersection must be pressed.

A sensor that only gives volts or gnd as output cannot be used.


To emulate four switches you can use a CD4016 Quad Bilateral Switch. Each of the four 'switches' has a CMOS input that will close the switch if HIGH and open the switch if LOW. If your sensor has an 'active LOW' output you will need a CD4049 or CD4069 hex inverter to invert the signal. If your sensor has an Open Collector or Open Drain output be sure to provide a pull-up resistor.

Thanks. I'll give it a try