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Ultrasonic receiver and transmitter

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abhaybonds

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I tried making a ultrasonic transmitter and receiver using the information given in the following link https://www.leang.com/robotics/info/articles/minison/minison.html

I made the transmitter and reciever circuits. Both the circuits individually work fine i.e. the frequency of both the transmitter and reciever is shown to be 40 Khz when checked with oscilloscope at the appropriate points of the circuit as told in the link.
Even the output of the receiver circuit shows a high output at pin 8 of LM567 and when a step voltage of frequency 40khz is applied at the point of connection of ultrasonic receiver the output becomes low.
But when I connect the ultrasonic transmitter/transducer and receiver to the circuit I dont get the desired results.
Is it because I connectd the sensors in the opposite way i.e opposite polarity. Do these sensors have any polarity. If yes, could you please tell me the correct polarity . If no, what else could be the problem
Please help.
I have these kind of sensors https://images.elektroda.net/26_1264077135.jpg they have some black ring at one pole.
 

karesz

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Hallo,
could you please tell us the correct type of your sensor, do you have a datasheet from it?
K.
 

FvM

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Polarity doesn't matter for ulatrsonic piezo sensors. The sensor looks like a standard 40 kHz sensor. It should provide
a sufficient receiver level to work even with a LM741 preamp, assuming correct frequency adjustment of LM555 and LM567.
 

Audioguru

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FvM said:
Polarity doesn't matter for ulatrsonic piezo sensors. The sensor looks like a standard 40 kHz sensor. It should provide
a sufficient receiver level to work even with a LM741 preamp, assuming correct frequency adjustment of LM555 and LM567.
The gain of an old 741 opamp at 40kHz is only 15 to 20. The low input resistance (1k) of the inverting 741 amplifier reduces the output level of the receiver sensor.

I suggested a non-inverting higher input resistance TL071 opamp with a gain of about 95.
 

FvM

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I agree, that it's a kind of ridiculous to use a 741 for the circuit, but expect it still to work. However, if the gain would be 20
(I assumed 25), then the input impedance also rises to 50k, which is O.K. for the sensor. Most likely, the circuit is not failing
because of utilizing a 741. There is also a risk of setting the gain too high and trigger the tone decoder permanently by
simple crosstalk, either electrical or acoustical.
 

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FvM said:
I agree, that it's a kind of ridiculous to use a 741 for the circuit, but expect it still to work.
Either the circuit is 30 years old or more or it was designed by a school kid who was taught only about the lousy old 741 opamp.
Look at the gain setting resistors (1M and 1k): it doesn't have anywhere near a gain of 1000.
 

razibgsm

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abhaybonds said:
I tried making a ultrasonic transmitter and receiver using the information given in the following link https://www.leang.com/robotics/info/articles/minison/minison.html

I made the transmitter and reciever circuits. Both the circuits individually work fine i.e. the frequency of both the transmitter and reciever is shown to be 40 Khz when checked with oscilloscope at the appropriate points of the circuit as told in the link.
Even the output of the receiver circuit shows a high output at pin 8 of LM567 and when a step voltage of frequency 40khz is applied at the point of connection of ultrasonic receiver the output becomes low.
But when I connect the ultrasonic transmitter/transducer and receiver to the circuit I dont get the desired results.
Is it because I connectd the sensors in the opposite way i.e opposite polarity. Do these sensors have any polarity. If yes, could you please tell me the correct polarity . If no, what else could be the problem
Please help.
I have these kind of sensors https://images.elektroda.net/26_1264077135.jpg they have some black ring at one pole.

26_1264077135.jpg
 
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abhaybonds

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thanks for the help.
About the polarity of the sensors. If the polarity doesn't matter is there any reason that the two poles have been marked distinctly.
26_1264077135.jpg

Also many people pointed out about the gain resistors for 741. Could anybody please tell me what would be better set of resistors.
@ audio guru. Does the rest of the circuit while using TL071 remains the same?
Also is the output given by the receiver sensor a normal square wave with low voltage or something else?
Also I read about increasing the range of the sensors by the appropriate setting of some of the resistors. Could anybody please also tell me about it?
 

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The poor old 741 opamp has a gain of only 15 to 20 at 40kHz so its output will be very low level.
The TL071 plugs straight in with the same pins as the 741 opamp and has a gain of 95 at 40khz so the output level or range is much more.

The resistors (1M and 1k) try to set the gain to 1000 but the opamps have poor response at a frequency as high as 40kHz.

The transmitter and receiver transducers are resonant at 40kHz so the received signal is a sine-wave. Also, the opamp in the receiver has much less gain at harmonics of the 40kHz.
 

FvM

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is there any reason that the two poles have been marked distinctly
They are not marked, but one terminal is grounded to the case. Basically, the sensors have a defined relation of acoustic
phase to applied voltage, but it doesn't matter in your application.

Before you think about increasing the amplifier gain, you should better determine the required sensitivity empirically.
 

abhaybonds

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@audioguru thanks for your reply.
@Fvm could you please explain what you meant by determining sensitivity emperically.

Also could somebody help me in my doubt about increasing the range of the sensors. Does it depend only upon the sensors used or also on the circuit. Please somebody explain and Pls. give me some link or some tutorial on this.
 

FvM

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what you meant by determining sensitivity emperically
Simply try the achievable range. Or measure the level of the amplified signal wth an oscilloscope.
 

Fugitive666

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help me... having same problem....i am using gl40 2r/2t set...circuit is working properly but the receiver does not receive the transmitted signal........the schematic can be viewed belowUntitled-1.jpg
 

Audioguru

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A lousy old LM358 dual opamp has trouble with frequencies above 1kHz and you are trying to receive 40kHz with it??
Use a better opamp. A TL072 dual opamp works perfectly up to 100kHz but its minimum supply is 7V.
 

Fugitive666

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how about 741...amplifying in two stages and passing it through tone decoder...
 

FvM

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It's correct, that two slow amplifiers (LM358, 741) can be used instead of a faster one. The circuit as is requires however a single supply OP, so it won't work neither with TL072 nor 741. Of course, there are much better modern types, but you possibly don't get them at a DIY store. Referring to the circuit from post #14, it absolutely should have a linear preamplifier, that means an amplifier with suitable input bias. I'm sure that a lot of better circuits have been published at edaboard before.
 

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The very old and lousy 741 opamp is 43 years old! It is designed for a 30V supply.
TL071 single, TL072 dual or TL074 quad opamp are much better (and since they are used a lot might cost less than a lousy 741) and should be used.

ANY opamp can use a single supply voltage if its input is biased at half the supply voltage and signal coupling capacitors are used.
 

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ANY opamp can use a single supply voltage if its input is biased at half the supply voltage and signal coupling capacitors are used.
Of course you're right. But the circuit must be changed.
 

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