Op amps boosting Ultra sonic signals?

[lazcook]

Im an industrial designer, and have started to learn about electronics and have building a simple bat detector circuit. The circuit is shown below but there is not enough gain from the signal to light up the led. All I want the circuit to do is light up an led when there is a signal at 40khz.

I need to use a series of inverting amplifiers to boost the signal. Could anyone show me how to integrate the amplifiers in the circuit below so that the led will light up with it detects a ultra sonic sound. In research I have found that a boost of around 4,000 times the original signal is needed.

My circuit

**broken link removed**

What I need to put into it

**broken link removed**


Thanks for your help any suggestion on how to do it would be appreciated!
cheers

 

[chemelec]

First off, there should be Plenty of gain in the circuit you show.

However:

1) That 10K resistor in series with your LED is WAY TOO HIGH in Value.

2) The Output Signal is at 40Khz AC.
*** LED's Need DC to operate properly.

3) I would Recommend using an Active Peak Detector Circuit.

*** I Can supply you a schematic if Needed.

 

[Oznog]

Much more impressive- though a bit more complicated- would be a circuit that can lower the frequency so you can hear it.
http://www.users.globalnet.co.uk/~courtpan/timeexpan.htm

 

[audioguru]

Hi Lazcook,
I answered you on the other website. The old LM358 is much too slow for 40kHz. Its max output drops above only 5kHz and at 40kHz it has a max gain of only 10.
Use 3 stages of a wideband TL074 quad opamp.

 

[Lilikin]

i would go for the tlo82 dual package and high input impedance this is a real beast you could get away with open loop gain but prob not

 

[Nigel Goodwin]

You might also consider that a 40KHz transducer is quite narrowly tuned, what makes you think bats use that exact frequency?.

 

[lazcook]

I know that 40kHz is too small to really check for all species of bat, the pip 45 and the pipistrelle 55 is one of the most common bats in the UK so I figured that a 40kHz transducer is the best and easiest to get hold of.

This circuit does not have to use all frequencies as it is part of a design project for the exterior casing as well as the insides. I’m an industrial designer hence why I’m asking for advice with electronics so the main aspect is focusing on the aesthetics and ergonomics etc... of the detector.

Spent a while today in the labs running 3 x 358op amps to give it more gain of the signal- cant get hold of the other ops amps yet. couldn’t get the circuit to work for sum reason??

chemelec- it would be very helpful if you could provide a schematic!

thanks for your feedback guys and keep it comming!

Laz

As long as I make a working circuit on a breadboard to show how it would work- lighting up an led when i receives a signal, it will be fine.

 

[mcs51mc]

Laz, take a look a this site **broken link removed** you will find all you need on US systems with very clear explanation on transmitter, receiver detection, ...

 

[audioguru]

Notice how the Japanese circuit uses a wide-bandwidth dual opamp. It also has a rectifier following the the amplifier. The rectifier's output is filtered with a capacitor so that the output is steady without flickering on and off.