An ultrasonic switch

Thread Starter


Joined Oct 28, 2007

I am beginning in Electronics. First, I'd like to build an ultrasonic switch, that woult light a led when a button is pushed. I have done the circuit of the emitter. But i have some troubles using the US sensor...

Here are the datasheets I have found for my US sensor (I have the MA40B8R) :

Nonetheless, I have tried to draw a circuit of that ultrasonic receiver. I used this drawing, which is in the end of the datasheet :

The problem is that I do not really understand that drawing (you also have to know that I am french, and so, I do not understand English so much. Sorry for the mistakes I have made...). And the battery is not represented in that circuit : that is why, as I am a beginner, I do not really know where to put it... I have drawn that circuit :

I have understood that when it receives a 40 kHz signal, the US sensor produces a current that will be increased by the OP-AMP. I have chosen the LM 324. Do I have to choose another one? The opamp is in inverting mode : how should I put my led in that circuit? Should I turn my Led in the other side? In fact, I have understood that the receiver transmits a current only when it receives a 40kHz signal. Should I nevertheless filter that signal? Do I need that 47 nF capacitor?

Here :


In fact, I have chosen a gain of about 50 because I would need a current between 3V and 6V to light my Led. But the problem is that I do not know the value of the current that will be produced when the sensor receives a signal. How could I find that value??

And finally, is that circuit right? Else, how should I link the sensor to my battery? Is 6 Volts enough??

Thanks for all.


Joined Sep 21, 2007
At first sight it looks like that circuit will produce a 40 Khz AC on the LED and the LED will light on the positive cycles and go dark on the negative cycles but the eye will see it lighted because of the persistence of the light.


Joined Jan 28, 2005
For what it is worth, your written English is very very good. Were it not for your admission to being French, I would have never known.

That said, I will leave the answering of your question to members with greater experience in the application of ultrasonics.