- #36
yungman
- 5,742
- 290
nadersb said:First let me thank all of you, all of you are very kind too me;) and sorry for my bad english;)
as I said before I am busy a little bit and I can't work on my project these pas days, I will continue on Saturday, so please give some time to test your ideas and tell you the results;)
and about mr.yungman's comment, let tell you about the circuit, (I don't want to hide anything, I appreciate your help) the circuit is an ultrasonic receiver, we have another circuit that is transmitter, it works perfectly and it sends ultrasonic waves,it has a transducer too
receiver circuit detect these ultrasonic waves(so its input is only 40 khz not a band) first we amplify input,then with two diodes and one capacitor we convert it DC voltage(I am not sure that convert is right verb for here!) after that we have a comparator, CA3140, it compares pin 2 with 3 and if 3 is bigger than 2 its output(pin6) becomes 6.8V .after that we have 2stages of transistors to amplify current because we want to drive a relay so we need high enough current.
about the transducer, it does not have datasheet, I asked someone and he told me this, so I can't help you with this. is there any question yet?!
If you don't have the data sheet, then we have to reverse engineering a little. Follow my post on #29. I want you to tell me what is R1 and R2 now. Then change R2 to 1/10 the value and tell me the output of the first amp. Then change to 1/20 value and tell me the output. From that, I can tell what is the transducer output.
You need to get a new op-amp. OP37 is a place to start. When you see signal at pin 2 of the op-amp, that is a tell tale sign your op-amp is running out of steam.
Regarding to noise. I want you to verify where the noise come from.
1) Disconnect the transducer, then short the input on the capacitor side to ground to verify whether the noise is still there. If so, the noise is from the electronics. I don't think so from my experience.
2) Re-connect the transducer. This time cover the transducer so it does not detect any signal. Look at the noise. If the noise is still there just as strong, your noise source is the transducer. Again I don't think so.
IF both 1 and 2 are negative, your problem is the environment. The only thing you can do is using band pass filter. I see you are rectifying the signal, so phase is not important. There is a lot you can do to filter. We use parallel LC tank at the front end and tune at 40KHz.
Like Jim Hardy said, why do you limit yourself to 9V? Is it a hand held device?
Just do all these first, get you amp working, characterize the detector. Then we work on the noise. It should be easy.
Last edited: