Home > Circuit Blox > Buggy Collision Detector

UPDATED:.01:02 03 January 2019

This buggy will turn about 120 degrees anticlockwise whenever it detects an obstsacle in front of it. An Ultrasonic Astable Blok with a transducer attached generates the sound wave. When the receiver detects a large enough reflected signal, it triggers a relay which reverses one of the motors for a second or two, causing the buggy to rotate and change direction.

The ulrasonics need to be mounted parallel to each other facing forwards.

To reduce sensitivity, detune the astable slightly so it runs slightly off its optimum frequency.

The motors and gearboxes are meant to be exactly the same in the video you can see the buggy veering to the left instead of straight..

An ultrasonic wave is continuously transmitted in front of the buggy. When a signal is reflected back from an obstable, one buggy motor reverses. Apologies for the photo, I couldn't find a better one.

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





    Ultrasonic Astable:
    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: Ultrasonic 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.


    The astable is connected to a transducer (TX) which continually transmits a 40KHz sound wave.

    When this signal is reflected off an obstacle, the receiver (RX) picks up the signal. The detector responds to changes in signal level and produces a low output pulse.

    This pulse triggers the monostable which activates a relay for a fixed period of time - up to 2.5 seconds.
    Alter VR1 to change length of the reverse time.

    The relay has dual sets of contacts - DPDT and is wired to reverse the motor connections when activated.

    Buggy Project.
    Can be used as part of a buggy project with sensors mounted on the front. An oscilloscope can be used to monitor the reflected ultrasonic signal by connecting a probe to the bottom of R3 (1K resistor) on the Ultrasonic Detector.

    Gears, motors and gearboxes can also be covered in the course of the project.

    The buggy can also have mechanical bumpers that activate microswitches. The microswitch can be connected between the "-Trig" input of the Monostable and 0v.

    This can be done as well as having the detector connected. This will give extra detection against thin obstacles such as legs of stools and chairs.