Need Help with Ultrasonic receiving circuit

Thread Starter

vivek1925

Joined May 12, 2010
11
Hey, I have my project on Ultrasonic transducer and receiver circuit. I have already built my transmitter circuit using the 555 timer to give out 40khz.

But with the receiver, I have a two stage active amplifier LM386 which actually amplifies the signal and i also have a comparator and a delay circuit attached to my amplifiers in order to tune the signal.

This is the point where i cannot understand:confused: in order to receive the signal is it necessary to have the delay and the comparator circuit connected or just continue with th Flip flop toggle switch.

If anyone can help me out with any ideas please help me as I am stuck at this position.
 

Thread Starter

vivek1925

Joined May 12, 2010
11
Hey Kingdano , this attaachment shows three parts . the second part with q3 amplifier is where i find a problem.. whether to have the circuit or not . The third part is the toggle .

I want to clarify if I can skip the Q3 and the delay and carry in with the toggle instead.

thnks anyways
 

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Audioguru

Joined Dec 20, 2007
11,249
Look at the datasheet for the LM386 power amplifier.
It shows an important resistor in series with an important capacitor from its output to ground. This prevents it from oscillating at a high frequency.
A supply bypass capacitor must be used at each one. This prevents motorboating and oscillation.
For a gain of 200, a capacitor is supposed to connect between pin1 and pin8 instead of your piece of wire.
The LM386 is a noisy power amplifier. You should have used a low noise opamp instead.
 

Thread Starter

vivek1925

Joined May 12, 2010
11
yeah checked with a 0.1uf capacitor in order to have a gain of 200:). this amplifier started to saturate therefore in order to eliminate the noise i have an another stage of amplifier to actually concentrate on the transmitted signal.

But i am not sure how the waveform if that pin 5 of stage 3 amplifier should look like as I am not sure whether i am getting my tunning correct with the potentiometer or should i need a input signal of 40khz from the transmitter in order to check Q3 amplifier.
 

Audioguru

Joined Dec 20, 2007
11,249
Any amplifier clips when its output swing gets too close to the power supply rails. Simply turn down the volume control to eliminate clipping.
 
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