舊型電話按鍵盤改做數字鍵盤

電話按鍵盤試接 Raspberry Pi

舊型電話按鍵盤再利用

稍早時，曾在舊零件箱中發現一個數字按鍵盤，是很久以前我將報廢電話按鍵拆下用做 8051 控制電動門鎖的輸入按鍵。現在像這種 3x4 的數字鍵盤應該只需要 7 條信號線即可，但是這東西卻有 13 個接線腳位，因為年代久遠記憶早已模糊，所以重新將接線量出記下備用。我想以此鍵盤做一個可適用手邊正在玩的一些 mcu/mpu 板子的控制面板部件。

舊型電話按鍵盤接線圖

首先要清理接腳的線頭，焊接一組排針，以便與其他裝置配接以及在麵包版上做測試。原本 13 個接腳經跳線後會只用到 7 個腳位，分成 3 行(C1, C2, C3) 4 列(R1, R2, R3, R4)。

如何讀取按鍵盤上某鍵被按下？其實就是用程式做很簡單的掃描－依序分別控制各行信號輸出為 HIGH，此時判讀各列的信號，信號為 HIGH 的行／列交集處即是按鍵所在。


試接 Raspberry Pi

再來，要將整理好的數字鍵盤試接 Raspberry Pi 的 GPIO (General-purpose input/output) 腳位，寫程式操控 GPIO 信號。

控制 GPIO 有很多種方法，可以參考這篇「讓你的 Raspberry Pi 透過 GPIO 閃爍 LED 燈」的介紹，另外最新的 Raspbian 應該有內裝了 Wiring Pi: GPIO Interface Library for Raspberry Pi 套件也可用。

實際接線前，若是手邊沒有 Raspberry Pi GPIO 腳位圖，有個指令 gpio readall 可用來先確認 GPIO 的腳位配置，撰寫程式時也是要弄清楚使用的腳位代號到底是 BCM? WiringPi? 或 Physical? 否則會發現結果都不對。

pi@raspberrypi ~ $ gpio readall
+-----+-----+---------+------+---+-Model B2-+---+------+---------+-----+-----+
| BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
+-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
|     |     |    3.3v |      |   |  1 || 2  |   |      | 5v      |     |     |
|   2 |   8 |   SDA.1 | ALT0 | 1 |  3 || 4  |   |      | 5V      |     |     |
|   3 |   9 |   SCL.1 | ALT0 | 1 |  5 || 6  |   |      | 0v      |     |     |
|   4 |   7 | GPIO. 7 |   IN | 1 |  7 || 8  | 1 | ALT0 | TxD     | 15  | 14  |
|     |     |      0v |      |   |  9 || 10 | 1 | ALT0 | RxD     | 16  | 15  |
|  17 |   0 | GPIO. 0 |   IN | 0 | 11 || 12 | 0 | IN   | GPIO. 1 | 1   | 18  |
|  27 |   2 | GPIO. 2 |   IN | 0 | 13 || 14 |   |      | 0v      |     |     |
|  22 |   3 | GPIO. 3 |   IN | 0 | 15 || 16 | 0 | IN   | GPIO. 4 | 4   | 23  |
|     |     |    3.3v |      |   | 17 || 18 | 0 | IN   | GPIO. 5 | 5   | 24  |
|  10 |  12 |    MOSI |   IN | 0 | 19 || 20 |   |      | 0v      |     |     |
|   9 |  13 |    MISO |   IN | 0 | 21 || 22 | 0 | IN   | GPIO. 6 | 6   | 25  |
|  11 |  14 |    SCLK |   IN | 0 | 23 || 24 | 1 | IN   | CE0     | 10  | 8   |
|     |     |      0v |      |   | 25 || 26 | 1 | IN   | CE1     | 11  | 7   |
+-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
|  28 |  17 | GPIO.17 | ALT2 | 0 | 51 || 52 | 0 | ALT2 | GPIO.18 | 18  | 29  |
|  30 |  19 | GPIO.19 | ALT2 | 0 | 53 || 54 | 0 | ALT2 | GPIO.20 | 20  | 31  |
+-----+-----+---------+------+---+----++----+---+------+---------+-----+-----+
| BCM | wPi |   Name  | Mode | V | Physical | V | Mode | Name    | wPi | BCM |
+-----+-----+---------+------+---+-Model B2-+---+------+---------+-----+-----+
pi@raspberrypi ~ $ 

我的數字鍵盤需要用到 7 個 GPIO 信號...
三條輸出：C1－#11(GPIO.0), C2－#12(GPIO.1), C3－#13(GPIO.2)
四條輸入：R1－#15(GPIO.3), R2－#16(GPIO.4), R3－#18(GPIO.5), R4－#22(GPIO.6)

用 python 試做：

import RPi.GPIO as GPIO
import time

cols= [11,12,13]
rows= [15,16,18,22]
keys= [['1','2','3'],['4','5','6'],['7','8','9'],['*','0','#']]

def npscan(pin):
    GPIO.output(pin, GPIO.HIGH)
    time.sleep(0.05)
    for inp in rows:
        if GPIO.input(inp):
            print keys[rows.index(inp)][cols.index(pin)],"key is pressed @",str(
inp),"/",str(pin)
            time.sleep(0.1)
    GPIO.output(pin, GPIO.LOW)
    time.sleep(0.05)
    return

try:
    GPIO.setmode(GPIO.BOARD)
    for pin in cols:
        GPIO.setup(pin, GPIO.OUT)
    for pin in rows:
        GPIO.setup(pin, GPIO.IN, GPIO.PUD_DOWN)
    while True:
        for pin in cols:
            npscan(pin)
except KeyboardInterrupt:
    GPIO.cleanup()

測試結果：

pi@raspberrypi ~/playground $ ./numpad.py 
1 key is pressed @ 15 / 11
2 key is pressed @ 15 / 12
3 key is pressed @ 15 / 13
4 key is pressed @ 16 / 11
5 key is pressed @ 16 / 12
6 key is pressed @ 16 / 13
7 key is pressed @ 18 / 11
8 key is pressed @ 18 / 12
9 key is pressed @ 18 / 13
* key is pressed @ 22 / 11
0 key is pressed @ 22 / 12
# key is pressed @ 22 / 13

下一步

這僅僅是試做，下一步想要做的是將接線改裝成 I²C（Inter-Integrated Circuit）bus 介面，否則我的數字鍵盤幾乎用完了 Raspberry Pi 的 GPIO 腳位，實用性大大受限。