A $2 Picaxe08M2 uses a $1 ultrasonic sensor to measure distance and display on a $1 digital voltmeter. HC-SR04 sensor is hacked for one-pin use. PWM signal to DVM only uses one pin, so only 2 pins on the 08M2 are used. Simple code uses built-in ULTRA and PWMOUT commands:
do
ultra 1,b2
w0=b2*215/100+12
pwmout pwmdiv4, 2, 249, w0
loop
