as it ws said...the transducer can act as a capacitor, therefore it doesnt need a capacitor...about what you said...can i have some illustration?R00KIE said:I would put a capacitor in series with with the transducer, 10nF or 100nF will do just fine.
I can't really see the point of R3 and C4 but I guess there must be a good reason why they are there.
If that doesn't work then I guess you need to come up with a circuit (understanding the concept of what this circuit should do helps a lot)
If a new circuit is needed I think the gain of the second stage may be a bit too high, if you really need a gain of 1000 maybe you could try to split it between the two stages (unless the noise contribution of the first stage is a problem and it really needs to be that way, input impedance can also be a limiting factor there but in that case you could try using a non inverting schematic at both stages (very high input impedance)).
yha i have..ang it operate at 40khz...sFvM said:I expect, you have a piezo transducer (they should use a circuit symbol with a capacitor inside the circle for clarity), then it's O.K. to omit a decoupling capacitor at the input.
U1B can't achieve the gain of 100 set by the resistors, cause it has about 1 MHz GBW, resulting in a gain of 25 a 40 kHz for example, but 25 may be sufficient as well.
There's only one serious fault in the circuit to my opinion, U2 (that has an open collector output) is missing a pullup resistor, thus the output voltage is always zero. Install an 10 k or 100k resistor (the value creates different time constants for the switch output) to +5V at the output, and the circuit is operational.
GBW =gain bandwidth? can you explain further? and about that 25?U1B can't achieve the gain of 100 set by the resistors, cause it has about 1 MHz GBW, resulting in a gain of 25 a 40 kHz for example, but 25 may be sufficient as well.
i read the datasheet..it really need a pull-up on the output for a comparator...ill try it...the output is always zero!nstall an 10 k or 100k resistor (the value creates different time constants for the switch output) to +5V at the output, and the circuit is operational
Somewhat simplified, the amplifier gain at a certain frequency can't be higher than GBW/f. You can see this from the open loop response diagram in datasheet.GBW =gain bandwidth? can you explain further? and about that 25?
Obviously, an existing application circuit can't answer the question if a decoupling capacitor is necessary. May be the author simply didn't understand the device.Just as a curiosity (and it seems there are more than one type of piezo transducers, this ones do need a capacitor in series, check the lower part of the schematic).
im making something like that...but i think it must be discuss on Microcontroller...
THE RESISTOR WAS VERY USEFUL!R00KIE said:Ok the pull-up resistor was kind of basic, I don't know why i didn't see that(maybe because I didn't look at the datasheet ^^;;; ) but like FvM said and very well it is needed.
As for the schematic at the input connect the piezo and it should work just fine.
Just as a curiosity (and it seems there are more than one type of piezo transducers, this ones do need a capacitor in series, check the lower part of the schematic).
https://www.robot-electronics.co.uk/htm/srf04tech.htm
Anyway with the schematic I show you you will have a second order high-pass filter (as opposed to the first order one made by C1 and R4, if the piezo doesn't act as a capacitor) and the gain is split between the two amplifiers. Then connect that to the comparator as it is (and don't forget the pull-up resistor).
Oh and by the way, at 40KHz the global gain is just 329 (simulated). I didn't try but I guess that if you want a gain of 1000 you need to add another stage and have a gain of 10 at each stage, as it is you may as well reduce the gain to 17 at the two stages and get the same output.
maybe very old...40 years??wow..it still work!!!Audioguru said:A piezo buzzer is completely different from a piezo transducer (speaker) that is used in this project.
The buzzer has a transistor oscillator circuit inside to make it buzz (beeeeep) when DC is applied.
A piezo transducer goes "tick" when DC is applied. It ticks again when DC is released. Its input is supposed to be an AC signal.
I wish the web would have an automatic warning: "This schematic is 40 years old. Better parts and circuits are available today".
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