The post discusses a few very useful yet simple ultrasonic transmitter receiver circuits which can used for many crucial applications, such as ultrasonic remote control, burglar alarms, electronic door locks, and for listening to frequencies in the ultrasonic range which are normally inaudible to human ears.
Many commercial ultrasonic gadgets work with a predetermined frequency and make use of transducers which are made to peak, or resonate, at the specific frequency. The restricted bandwidth and price of the majority of of such transducers cause them to become inappropriate for hobby and DIY implementations.
But in fact, that isn't an issue, since virtually any piezo speaker could be applied like a ultrasonic transducer for both, in the form of a transmitter output device and also as receiver sensor.
Although piezo speakers efficiency cannot be compared with the efficiency of a specialized, industrial transducer, as a hobby and fun project these can work perfectly. The device we employed with the below explained circuits was a 33/4 -inch piezo tweeter which is available from most online stores.
Simplest Ultrasonic Generator
Our very first circuit, is shown in the above Fig, is an ultrasonic generator which uses the well-known 555 IC timer in a adjustable frequency astable multivibrator circuit. The design outputs a square wave signal which, works with R2, for tuning through around a frequency range of 12 kHz to over 50 kHz.
This frequency range can easily be adjusted by altering the value of capacitor C1; employing a lower value will cause the range to go higher, while larger value will make the range that much smaller.
Ultrasonic Generator with Fixed 50% Duty Cycle
The next ultrasonic generator, revealed in the above Fig. 2, makes use of 6 buffer gates of a solitary 4049 CMOS inverting buffer IC.
A couple of the buffers, U1a and U1b, can be seen attached within a variable-frequency astable-oscillator circuit having a 50 % duty cycle, square wave output.
The rest of the 4 buffers all connected in parallel in order to enhance the output over the connected piezo element. This much better ultrasonic generator's frequency range is approximately similar to the previous IC 555 version. However, The major advantage of this design is its accurate 50% duty cycle around the full frequency range.
That said, the frequency range could be made higher by lowering the capacitor C1 value, and the frequency can be decreased by using higher values for C1. The 100k potentiometer, along with resistor R3, fixes the output frequency.
PLL Ultrasonic Generator
The LM567 phase-locked-loop (PLL) IC is used for generating ultrasonic frequency in our 3rd concept as proven in the above figure 3. This circuit provides a number of features better than previous two ultrasonic concepts.
First, the IC 567's in-built oscillator is developed to work within a incredibly large frequency spectrum, from under 1 Hz and as high as 500 kHz. The generator's output waveform, at pin 5, exhibits outstanding symmetry all through its performance range.
The generator additionally gives a increased output compared to other two circuits for the reason that output is matched much closely to the piezo tweeter's (SPKR1) impedance.
The output of the circuit could be tweaked through around 10 kHz to more than 100 kHz working with potentiometer R5. Transistor Q1 is hooked up like a common collector circuit in order to keep the 567's output aloof as well as to drive the output-amplifier circuit which is created using the transistors Q2 and Q3. The circuit could be changed into an ultrasonic cw transmitter by breaking the IC's pin 7 connection and inserting a switch key in series.
In that case, you will require some form of ultrasonic receiver to hear the signals; and that is the exactly what we are going to discuss in our next circuit.
Ultrasonic Receiver Circuits
A ultrasonic receiver circuit using a 567 PLL IC that features a frequency tuning capability is shown in the above diagram. The IC's tunable oscillator circuit is identical to the earlier generator circuit, and handles exactly the same range of frequency. An LED is positioned at the pin 8 detector pin of the IC which quickly indicates the detected signals.
Transistor Q1 is positioned to amplify the minute ultrasonic signals detected by the piezo device and forwards them onto the PLL.
How to Test
To test the ultrasonic working, switch on the IC 567 ultrasonic generator circuit and move the transmitter piezo all through the area. Beginning with the minimum setting, fine-tune R5 bit by bit until you are unable to listen to anything from the speaker. This should fix the circuit's output frequency approximately to 16 and 20 kHz, depending in your ear's sensitivity to high-frequency.
Now, switch on the ultrasonic receiver circuit and position its piezo transducer at approximately 12 inches away from the generator's speaker, although having itaimed in the exact same direction. Adjust the receiver through R5, beginning from the minimum frequency point (which corresponds to the pot's maximum resistance range), and little by little maximize the frequency until yo see the receiver's LED just illuminating.
If you see receiver not responding to the transmitter output signals, try aiming the receiver's piezo accurately the generator's speaker and keep doing this persistently. As soon as the receiver detects the signal and the LED lights up, move the two Tx/Rx piezo away by a a minimum of ten feet and begin fine tuning yet again.
Once you find all is performing satisfactorily, you can make use of the the transmitter's attached telegraph key (optional at pin7) and check out the LED response on the receiver.
The LED must respond to this by flashing in the the dot-and-dash style as tapped by you using the telegraph key. An additional application of this ultrasonic generator/ receiver set can be in the form of a straightforward burglar alarm sensor.
Attach a 5 V relay across pin 8 of the receiver's LM567 and the battery's positive pole. Arrange the Tx and the Rx piezo devices approximately a foot apart and focused within the same path, but clear of any nearby object.
If a person goes in close proximity to and in front side of the a pair of speakers the ultrasonic frequency will be reflected back triggering the receiver's relay to switch ON. The output contacts of the relay could be applied to switch on an alarm or a siren device.
Highly Sensitive Ultrasonic Receiver Circuit
The last ultrasonic receiver circuit design is actually an extremely sensitive ultrasonic receiver which can easily pick up almost anything within the ultrasonic frequency range. You possibly can listen to insects, bats communications, engines, etc.; the idea could also be used in conjunction with the above explained ultrasonic generators for developing high quality ultrasonic systems.
The design, works using the principle of direct conversion. Transistors Q1 and Q2 boost the ultrasonic signals detected by the piezo speaker. The Q2's collector output is then used to drive the JFET (Q3) input, which can be seen hooked up like a product-detector circuit.
The PLL (U1) stage in this concept is employed like a tunable heterodyne oscillator which additionally feeds the input of the JFET detector circuit. The inbound ultrasonic signal combines with the frequency of the heterodyne-oscillator generating a sum and difference frequency.
The high frequency element is filtered out through the C3, R8, and C6 component network. The leftover low frequency output is allowed to enter across the LM386 audio amplifier input. A speaker or headphones could be attached to the circuit's audio output.
Another Ultrasonic Receiver Circuit for listening to Sounds above 20 kHz range
The frequency detection range of the our ear is hardly up to 13 kHz frequency. The function of the ultrasound detector is to defeat this limitation by switching the frequency of high frequency noises for example dog whistles, barely audible gas leaks, bat bleeping, and several artificial ultrasonic sounds for example lightly tapping on a newspaper.
The 'ultrasound' detected by the input transducer is boosted and fed to a product detector. An astable multivibrator is included since the BFO stability may be not be of much significance. In addition for the required signal differential, the circuit additionally generates the BFO signal on its own as well as the summing frequency, which is then terminated inside a low pass filter fixed at 4 kHz.
The signal resulting here is yet again amplified to operate a set of headphones. The circuit works with around 8 milliamps, therefore it can easily be powered from a 9 V dry battery.