Reading Values from Touch Keypad

This demonstration shows how to interact with the Raspberry Pi Touch Keypad. The Raspberry Pi Touch Keypad is required (https://www.seeedstudio.com/Raspberry-Pi-Touch-Keypad-p-2772.html).

The Raspberry Pi touch keypad supports up to 16 keys with adjustable sensitivity and built-in LD0. Touch keypad is read only, and has IIC interface connected to SDA1 and SCL1 on the Raspberry Pi interface. The I2C will read 2 bytes of data: Data_0 and Data_1.

Data_0: B7 ~ B0 is TP0 ~ TP7 on/off status. 0 is key off, 1 is key on.
Data_1: B7 ~ B0 is TP8 ~ TP15 on/off status. 0 is key off, 1 is key on.

1. Prepare the overlay

Download the overlay first, then select the shared pin to be connected to RPI header (by default, the pins will be connected to PMODA instead).



In [1]:

    
from pynq.overlays.base import BaseOverlay

base = BaseOverlay("base.bit")
base.select_rpi()

2. Instantiate the Microblaze

The Microblaze will control the pins on the RASPBERRYPI header.



In [2]:

    
%%microblaze base.RPI

#include "xio_switch.h"
#include "circular_buffer.h"
#include "i2c.h"

// Device constants
#define TOUCHPAD_DEV_ADDRESS         0x57

unsigned int get_touchpad_reg_value(){
    uint8_t data[2];
    i2c device = i2c_open_device(1);
    set_pin(2, SDA1);
    set_pin(3, SCL1);
    i2c_read(device, TOUCHPAD_DEV_ADDRESS, data, 2);
    return (unsigned int) ((data[0] << 8) + data[1]);
}

3. Read the key values

The available pin names are listed below.



In [3]:

    
PIN_MAPPING = {'circle': 0,
               'cross': 1,
               'square': 2,
               'r': 3,
               'home': 4,
               '+': 5,
               '-': 6,
               'l': 7,
               'down': 8,
               'right': 9,
               'up': 10,
               'left': 11,
               'power': 12,
               'rpi': 13,
               'logo': 14,
               'triangle': 15
               }

To convert the raw data into the value for each key, we define the following functions.



In [4]:

    
def reg2int(reg_value, key_number):
    return "{0:b}".format(reg_value).zfill(16)[-(key_number+1)]

def get_touchpad(key_name):
    reg_value = get_touchpad_reg_value()
    key_number = PIN_MAPPING[key_name]
    return reg2int(reg_value, key_number)

Run the following code without pressing any button.



In [5]:

    
get_touchpad('home')









    Out[5]:





'0'

While pressing gently on the home button of the touch keypad, run the following code.



In [6]:

    
get_touchpad('home')









    Out[6]:





'1'

While pressing the right arrow and square at the same time, run the following code. Note that there are 2 read commands issued, although 1 read command can get values for all the keys.



In [7]:

    
for key in ['right', 'square']:
    print('Key {} reads value {}.'.format(key, get_touchpad(key)))









    



Key right reads value 1.
Key square reads value 1.

4. Cleanup

Switch back the connection on the shared pin to PMODA header.



In [8]:

    
base.select_pmoda()