Home Code Connecting an AD keypad to a Micro:bit with Micropython example

Connecting an AD keypad to a Micro:bit with Micropython example

by shedboy71

I purchased this module as part of another microcontroller kit, its an interesting little module as it has 16 buttons but with only 1 I/O line is required, an analog input. Usually a keypad needs many I/O pins as you either have to read the individual keys or there is a pin required for the columns and rows

You simply connect this to your Micro:bit and read in the value.

The concept is straightforward  you use a resistor network as voltage dividers, and then let each button feed a different voltage to the analog pin. So by detecting the voltage you can tell which button has been pressed. You can only detect one button at a time. This means rather than muliple I/O pins being required you can use 1, it does mean you need to detect the analogue value of the button pressed and act on in your code but this is not that a difficult task

 

Here is the schematic of the module

We connect 3v to VCC, Gnd to Gnd and the AD to Pin 0 of the Micro:bit

Parts List

 

Name Link
Micro:bit Micro:bit Development Board
AD Keypad 5pcs/lot AD Keypad 16 4×4 Accessory board matrix buttons controlled ADC AD port keyboard Free Shipping
Edge Breakout I/O Expansion Edge Breakout I/O Expansion Extension Board for BBC micro:bit
Connecting cables Free shipping Dupont line 120pcs 20cm male to male + male to female and female to female jumper wire

Code

 

from microbit import *
 
while True:
    reading = pin0.read_analog()
    sleep(100)
    if reading < 990:
        print("Reading: " + str(reading))
        sleep(250)

 

Testing

Open up the REPL window and press the keys individually, take a note of the values displayed. Here is what I saw

Reading: 2
Reading: 67
Reading: 132
Reading: 198
Reading: 261
Reading: 323
Reading: 387
Reading: 452
Reading: 513
Reading: 577
Reading: 641
Reading: 698
Reading: 759
Reading: 822
Reading: 884
Reading: 945

You can then use these values, if you take a look at them you will see a range. Take key 2 which returned 67, you don’t want to look for exactly 67 but between a range of numbers. The difference between the values returned is around 60 so a good starting point would be 30 lower and 30 higher, so to detect key 2 being pressed you would do the following

if reading > 40 and reading < 94:
Do Something

 

from microbit import *
 
while True:
    reading = pin0.read_analog()  
    sleep(100)
    if reading > 1 and reading < 39:
        num = 1
    elif reading > 40 and reading < 94:
        num = 2
    elif reading > 95 and reading < 164:
        num = 3
    elif reading > 165 and reading < 218:
        num = 4
    elif reading > 219 and reading < 290:
        num = 5
    elif reading > 291 and reading < 354:
        num = 6
    elif reading > 355 and reading < 418:
        num = 7
    elif reading > 419 and reading < 485:
        num = 8
    elif reading > 486 and reading < 544:
        num = 9
    else:
        num = 0
    print("Number: " + str(num))

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1 comment

William Moore 30th May 2019 - 7:11 pm

This WaveShare AD Keypad is a good solution for limited input on a BBC Micro:bit and I had no problem making it work with MicroPython. However, when I use it on the ESP8266 using MicroPython for ESP8266, I have discovered that this keypad does not work well. Only the first 8 keys (K0 thru K7) return a value between 0 and 1024. Keys K8 thru K15 all return 1024. The sole ADC port on the ESP8266 only works for analog voltages between 0 and 1.0V, so I think part of the reason is that the keypad was being powered
by a 3.3V supply, and maybe it would work if I powered it thru a 1.0V supply. The other possibility is that the resistor network used for dividing the voltages produced via the 4×4 matrix keypad is not optimized for the ESP8266. I then decided I’d try it on the ESP-32 which advertises 16 pins capable of ADC use, but MicroPython for ESP32 only supports 8 pins for ADC channels (GPIO-32 thru GPIO-39). So, I was able to interface the WaveShare to one of these pins, but again, I could only get 5 keys (K0 thru K4) to give a unique value; the remaining keys all would return 4095 (the ESP32 ADC has 12-bits of resolution, not 10-bits). So again, my attempts at getting this Keypad to work with more powerful MicroPython chips was a bust. So, now I’m researching the problem via the Internet and came across this article and decided to leave my 2 cents worth…

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