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.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.
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.FvM said:I agree, that it's a kind of ridiculous to use a 741 for the circuit, but expect it still to work.
abhaybonds said:I tried making a ultrasonic transmitter and receiver using the information given in the following link **broken link removed**
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 http://obrazki.elektroda.pl/26_1264077135.jpg they have some black ring at one pole.
They are not marked, but one terminal is grounded to the case. Basically, the sensors have a defined relation of acousticis there any reason that the two poles have been marked distinctly
Simply try the achievable range. Or measure the level of the amplified signal wth an oscilloscope.what you meant by determining sensitivity emperically
Of course you're right. But the circuit must be changed.ANY opamp can use a single supply voltage if its input is biased at half the supply voltage and signal coupling capacitors are used.
Why don't people understand that it is EASY to bias an opamp properly so it works from a single supply voltage??Of course you're right. But the circuit must be changed.
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