An ultrasonic wave is continuously transmitted in front of the buggy. When a signal is reflected back from an obstable, one buggy motor reverses.
The length of time the motor reverses for, can be adjusted using VR1 on the monostable.
Use 40KHz transducers for the U/S TX and RX.
Circuit Voltage: 6 to 9 volts
Motor Supply: as required
Adjust VR1 with a screwdriver to "tune" the transmitter frequency. Move a hand in front of the sensors while tuning, look for the LED on the detector flashing. The tuned position of VR1 should be about midway.
Note: Astable is shown upside down.
Set the "Range" to 2, (0.05-2.5s) with VR1 midway.
For reliable operation, use 3 x100nF capacitors between the motor connections and the case. Motors produce very strong electrical interference.