AVR Freaks

Source code, in case anybody is interested.

#define F_CPU		1000000UL	// 1 MHz

#include <avr/io.h>
#include <util/delay.h>

#define SPKR_A		PA0
#define SPKR_B		PA1
#define KEY		PB0

#define CPO_FREQ	700	// hz
#define CPO_HALF_CYCLE	(F_CPU / CPO_FREQ / 2)


int main(void)
{
    DDRA = (1 << SPKR_A) | (1 << SPKR_B);
    PORTB = 1 << KEY;

    while (1) 
    {
	if (!(PINB & (1 << KEY)))	// key down
	{
	    PORTA = (1 << SPKR_A);	// pulse speaker +
	     _delay_us(CPO_HALF_CYCLE);	// 1/2 cycle
	     PORTA = (1 << SPKR_B);	// pulse speaker -
	     _delay_us(CPO_HALF_CYCLE);	// 1/2 cycle
	}
	else
	    PORTA = 0;			// no DC on speaker!
    }
}

5V wall wart not in the picture.  Was using clip leads for power, but have since soldered on a power jack (which the board is designed to take.)  Not a powered speaker - there's a 330 Ohm resistor in the circuit behind the speaker.

Shocking omission!

Still used on the ham bands, fairly heavily.  My son says it is used in video games, and that's what got him interested - that surprised me.  And definitely useful for debugging.

Should also be extremely valuable when the zombie apocalypse comes.