Here’s a nifty circuit to emit a “beep” every time your ZX80 or MicroAce reads from or writes to a selected memory address. Four comparators, the heart of the circuit, constantly compare the address on the bus to the address set on a bank of 16 switches. When the two are equal, a 555 timer is started, which runs another 555 oscillator. The tiny switches in the circuit must be set in binary, one digit at a time. The switch which would be used for A15 is left always grounded instead and compared to NOT MREQ. The schematic this page shows how to construct this circuit. Use a 2 inch 10 ohm speaker to emit the beep.
Now you can hear every time the computer executes a certain byte of code. Depending on what you set the switches to, you can hear the beep for nearly any occurence within your computer.
To get a beep when Set switches as Newline key pressed 0283 Keystroke ignored (NL with error, etc.) 03A7 Keystroke results in syntax error 08AE Character printed on the screen 4024 Printing on screen advances to a new line 4025 Rubout pressed 0395 Screen is cleared (By any method) 0747 Keystrokes in line beginning with illegal keyword 07BB
