Ultrasonic Circuits

This was one of my first designs: it is an ultrasonic parking sonar. Based on an ultrasonic amplifier from an article seen on a 1982 magazine, it was once installed on the rear bumper of my Volvo Station Wagon. It served very well for many years. Connecting it to the reverse gear lights, it switches on automatically and shows you the distance to the nearest obstacle (according to his beam) on a led scale. When the last led lights, a buzzer is also activated telling you to stop immediately.

Use this circuit to test if the light coming from your 40khz IR emitter is really emitting the right frequency. The schematic says to use a GP1U5X ir module, but probably any 40khz detector module will work.. I used a GP1U26X module.

The microphone has high sensitivity in the audio range, but in the ultrasonic range, the sensitivity decreases rapidly. The receiver is very sensitive. To prevent overdriving and feedback due to the high sensitivity of the microphone in the audio range, the gain of the amplifier should be low in the audio range and increase with frequency in the ultrasonic range.

This sensor uses the sound generator in the RCX to make a 15kHz audio tone, which is almost ultrasonic. The tone is received with circuitry similar to my Sound sensor. The output of a crystal microphone MIC is amplified and then only the very high frequencies are further amplified (see plot). This signal is enveloped detected with a diode D1 and capacitor C1. The voltage on the capacitor will equal the average volume of high frequency sound the microphone is picking up at any moment.

This sensor uses the sound generator in the RCX to make a 15kHz audio tone, which is almost ultrasonic. The tone is received with circuitry similar to my Sound sensor. The output of a crystal microphone MIC is amplified and then only the very high frequencies are further amplified (see plot). This signal is enveloped detected with a diode D1 and capacitor C1. The voltage on the capacitor will equal the average volume of high frequency sound the microphone is picking up at any moment.

This is a very basic infrared detector/emitter circuit. One major downside of this circuit, is that ambient infrared light will interfere with its detecting obstacles.

In this example, a BrainStem GP 1.0 microcontroller uses a SRF04 Ultrasonic Range Finder to measures distances to obstacles. The BrainStem GP 1.0 tells the sonar module to emit a "ping" and measure the time it takes to receive an echo. It reveals the distance as a raw time in increments of the timer's resolution which is 1.6 uSec. This example shows a Palm Pilot running the Console to display the sonar readings but any supported Platform could be used.

The sensor is derivated from Mike Gasperi's Almost Ultrasonic Motion Sensor . We added a forth amplifier-stage. The sensor is equipped with the cheapest crystal microphone. For each ear there are two audio-amplifier stages. The signal passes the diode D7. The positive peak charges C3 which is then discharged through R10 (the time constant T=RC=0,470E-6*1E5=0,047 sec). The peak-level is amplified and passed to the RCX through the 4th op-amp. The sensor has to be calibrated at R1. The RCX raw-values: +/-10-90.

This is a very interesting project with many practical applications in security and alarm systems for homes, shops and cars. It consists of a set of ultrasonic receiver and transmitter which operate at the same frequency. When something moves in the area covered by the circuit the circuit�s fine balance is disturbed and the alarm is triggered. The circuit is very sensitive and can be adjusted to reset itself automatically or to stay triggered till it is reset manually after an alarm.

These ultrasonic circuits are all quite old: my notes date them at mid-70s so they don't use ICs. Nevertheless there are several places where an op-amp would possibly simplify things. Despite their age I hope they are of interest: certainly basic principles don't change. This transmitter is designed to work with the next circuit as a remote control transmitter/receiver. It is only a single channel and you could once get multi-channel chips for the whole job. However ultrasonics have fallen out of favour commercially so I think most of these chips are now obsolete.