In our last post we talked about wanting explore the use of two I2C based io expanders in an old school application. If it werent for the fact that there was a readymade lcd library for the mcp23017 I would have swapped the io expanders. No Pull-ups, No Pulldowns and no decent documentation on the circuitpython libraries makes the AW9523 a sucky choice for an old school keyboard matrix. But Hey, F**k It Dog. Life’s A Risk. We are gonna make do with what we have.
Looking under the keyboard membrane and tracing the connectors we can get the following key map under a 4×12 array (16 pins).
0123456789A(10)B(11) -------------------- 0) *# ZXCVBNM/ <STOP> 1) -LASDFGHJK<N/C><ENTER> 2) 0912345678<BS> <START> 3) POQWERTYUI<CAN><DIAL>
Of course for this to work we needed to solder 10k pull up resistors on all but the last 4 pins (8-11). This was relatively straightforward since there is a strip of connectors to VIN on the board. Still, kind of a pain. On the other hand I have reals of 10k resistors and I guess I have time.
Here is a simple circtuitpython program which presents a prompt and then puts characters scanned by the keyboard onto the display.
import time import board import busio import adafruit_character_lcd.character_lcd_rgb_i2c as character_lcd import adafruit_aw9523 keymap= keymap.append('*# ZXCVBNM/\001') keymap.append('-LASDFGHJK\r\n') keymap.append('0912345678\010\002') keymap.append('POQWERTYUI\030\004') lcd_columns = 24 lcd_rows = 2 i2c = busio.I2C(board.SCL, board.SDA) lcd = character_lcd.Character_LCD_RGB_I2C(i2c, lcd_columns, lcd_rows) lcd.message = "PiTerm 1986 v0.0\nOk >" aw = adafruit_aw9523.AW9523(i2c) row_pins = [aw.get_pin(8),aw.get_pin(9),aw.get_pin(10),aw.get_pin(11)] for pin in row_pins: pin.switch_to_output(value=True) col_pins = [aw.get_pin(0),aw.get_pin(15),aw.get_pin(14),aw.get_pin(13), aw.get_pin(12),aw.get_pin(7),aw.get_pin(6),aw.get_pin(5), aw.get_pin(4),aw.get_pin(3),aw.get_pin(2),aw.get_pin(1)] for pin in col_pins: pin.switch_to_input(value=True) old_row=0; for pin in row_pins: pin.value=1 switch_state = [[0,0,0,0,0,0,0,0,0,0,0,0], [0,0,0,0,0,0,0,0,0,0,0,0], [0,0,0,0,0,0,0,0,0,0,0,0], [0,0,0,0,0,0,0,0,0,0,0,0] ] while True: for r in range(4): row_pins[old_row].value=1 row_pins[r].value=0 old_row=r for c in range(12): if (col_pins[c].value==0 and switch_state[r][c]==0): switch_state[r][c]=1 print(keymap[r][c]) lcd.message+=keymap[r][c] if (col_pins[c].value==1 and switch_state[r][c]==1): switch_state[r][c]=0 time.sleep(0.01) # debounce