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Transceiver ultrasound no echo signal

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kinsey

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hi guys, i am working on the transceiver ultrasound sensor, but still not get the echo signal.
these is my circuit
my programmer is working like this: MCU send 10 pcs 40khz square wave to the transformer (ratio 1:10, the 1st side connect 12V DC power, then the 2nd get 120 V ouput) .
but the circuit still no echo signal.

when i use oscilloscope to check the apmp 1 & 7 foot these is nothing.
when i check the transceiver ultrasound senosr foot, still no echo signal when i move the sensor close or far away to a wall.
(changed 2 more sensors, same status)

looking for advice.

thanks in advance.

kinsey
 

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Hi,

the echo may be a very small signal.

Why are pins 3 and 4 shorted at the transformer? Doesn´t this short circuit the transmit and receive signals?
The BJT needs to be high impedance in times where you expect the echo. Please confirm this by sending a scope picture of the bjt base signal..

The transmit burst is 250us in time. Please confirm this by showing a scope picture of transformer pin#5.
This equals to 75mm distance in free air, or about 37mm distance.

What is your expected measurement range?
Did you read about logarithmic receiver amplifier circuits? If not, then do so. Maybe this is what you need.

Klaus
 

You should confirm that your receiver is recovering from the transmit overdrive fast enough to detect the echo. Most transceivers use a transmit/receive switch to prevent receiver overdrive.
 

i too was thinking it was there but too small to see. Use a gated amplifier that turns off for the pulse, but is on during the return
 

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