Ultrasonic circuit explination

[Corky]

is their a way of simulating this or do i have to build it and test? cheers again

 

[audioguru]

I have not 'scope'd it but I suspect that the 40kHz piezo transducer is series resonant and the square wave drive from the 555 produces ringing on each edge. The ringing causes the voltage spikes.

EDIT: A SIM program probably knows nothing about a piezo transducer.
Built the circuit and try it. It has high gain at a fairly high frequency so do not use a solderless breadboard.

 

[chemelec]

The Piezo is basically just a Piezo Speaker, Sharply Resonant at 40 Khz and its harmonics to a lesser extent.

I Built it on a Solderless Breadboard. No Problem.

Output of Recieve Transducer is Mainly Sharp Spikes.
Putting my Hand in front of the Two Transducers Creates Sine Wave signals, Overriding the Sharp spikes at the output of the Recieve Transducer.
Moving my hand creates Varying Sine Frequencies.

I Agree, I Doubt you can Simulate This in any of those programs.
(Unless one has a Perfect Speaker and Microphone, than that Might some what work.)

 

[ericgibbs]

I Built it on a Solderless Breadboard. No Problem.

hi chemlec,
I agree, no problems at all with bread board construction for this project.
Why members continue to post rubbish about bread boards, because they don't know how to use them, beggars belief.!

IIRC 'jimB' did some practical tests on bread boards and posted the results on ETO.

LTSpice can give a very good approximation of these circuits driving ultrasonic transducers.

E

 

[Maged]

Hello,
Here is that circuit redrawn so it shows the following points.
1- the Tx transducer is connected via 1Meg ohm which will kill any output from it. It should be connected to half the supply voltage or at least a capacitor divider
2- In addition to connecting the Rx Transducer to Vcc (as most of you have said) which is not mentioned in most transducer's data sheets, is connected to Op-amp section A , the output of which is NOT connected to anything, rather its -ve input is connected as an output to the second op amp, so no output is expected.
The 555 in this circuit is known as 50% duty cycle generator as the one resistor from the output charges and discharges the capacitor making the times equal, however it may not simulate well as it depends on how the simulator see the internal components of the real thing, and this is the CMOS version too.. I tried this circuit several times and worked fine except the exact 50% is not as expected, the reason is the output loading makes different charge and discharge currents as load may take or give current.

 

[audioguru]

1- the Tx transducer is connected via 1Meg ohm which will kill any output from it. It should be connected to half the supply voltage or at least a capacitor divider.

No.
The piezo transducer does not conduct DC. Its AC impedance is about 900 ohms at 40kHz. Its common wire should be connected to ground like in the Maxim schematic.

2- In addition to connecting the Rx Transducer to Vcc (as most of you have said) which is not mentioned in most transducer's data sheets, is connected to Op-amp section A , the output of which is NOT connected to anything, rather its -ve input is connected as an output to the second op amp, so no output is expected.

Most of us agree.

The 555 in this circuit is known as 50% duty cycle generator as the one resistor from the output charges and discharges the capacitor making the times equal, however it may not simulate well as it depends on how the simulator see the internal components of the real thing, and this is the CMOS version too. I tried this circuit several times and worked fine except the exact 50% is not as expected, the reason is the output loading makes different charge and discharge currents as load may take or give current.

The output to the Tx transducer does not need to have a perfect 50% square wave. The three divider resistors in the 7555 must be matched and the transistors must be matched to produce a perfect square wave.

 

[audioguru]

hi chemlec,
I agree, no problems at all with bread board construction for this project.
Why members continue to post rubbish about bread boards, because they don't know how to use them, beggars belief.!

The gain of the three non-inverting opamps is about 500 times so it does not take much stray coupling capacitance from pin 1 to pin 10 of the quad opamp to make a 40kHz oscillator.
The rows of contacts on a solderless breadboard and its many jumper wires have stray capacitance all over the place.

 

[Corky]

ive got some parts coming tonight hopefully the op amps i ned will be included, ill give it a go on a breadboard and get back to you cheers again

 

[ericgibbs]

The gain of the three non-inverting opamps is about 500 times so it does not take much stray coupling capacitance from pin 1 to pin 10 of the quad opamp to make a 40kHz oscillator.
The rows of contacts on a solderless breadboard and its many jumper wires have stray capacitance all over the place.

You are not listening to what others are finding and explaining to you, the circuit will NOT burst into 40KHz oscillation, if the bread board is used properly.!

If you post a photo of your bread board perhaps I would be pleased to point out what you are doing wrong.

I have used bread boards to check out circuits using almost every type of semiconductor and I have never had a problem, do the layout correctly and a circuit will work.

You posted a long time ago, that you had used a bread board only one time and the circuit didn't work correctly, surely you cannot base on a one time trial, a meaningful conclusion in trying to influence other prospective users against using bread boards.?

 

[Corky]

does the transmitter have to have an AC signal or is a squarewave DC ok? i read that they must have AC but then these circuits are using dc squarewaves?

 

[ericgibbs]

does the transmitter have to have an AC signal or is a squarewave DC ok? i read that they must have AC but then these circuits are using dc squarewaves?

hi Dale,
A square wave is fine!
Eric

 

[Corky]

cheers eric, i did think so just double checking

 

[audioguru]

does the transmitter have to have an AC signal or is a squarewave DC ok? i read that they must have AC but then these circuits are using dc squarewaves?

Since a piezo transducer does not conduct DC then feeding it a square wave with DC on it is fine.
A speaker with a voice coil must be fed AC without any DC on it.

 

[audioguru]

You are not listening to what others are finding and explaining to you, the circuit will NOT burst into 40KHz oscillation, if the bread board is used properly.!
If you post a photo of your bread board perhaps I would be pleased to point out what you are doing wrong.

Every photo posted here of a circuit built on a solderless breadboard is a messy tangle of wires with no regard to proper layout.

 

[ericgibbs]

Every photo posted here of a circuit built on a solderless breadboard is a messy tangle of wires with no regard to proper layout.

Your above statement fully supports what I and others have repeatedly told you.!, its not the bread board thats the problem, its the incorrect layout.
Would you agree if the bread board circuit is built correctly the circuit will work as expected.??

If so, why don't you advise any OP thats got a bread board problem circuit, the CORRECT way to connect it up.? rather than blame bread boards as a whole.

Its a photo of a bread board you have connected we want to see, not some struggling wannabe, so that we can tell you what you are doing wrong.

 

[chemelec]

Before I go, Here is My Prototype.
Leaving Today for Australia.
Take Care All of you......Gary

 

[audioguru]

Chemelec, your breadboard layout does not look very neat and tidy but I am glad that it works for you.

 

[chemelec]

Chemelec, your breadboard layout does not look very neat and tidy but I am glad that it works for you.

It is Perfectly Functional.

I Don't Trim my Resistors and Capacitor leads down as it would result in a Waste of parts.
If I did, the Leads may be too short for the Next Project
I use these parts over and over again (About 1000 of them set aside, just used for Breadboarding) And I breadboard Many Circuits Every Week.

 

[Corky]

ignoring the op amp bit can someone please advise why im only getting 20mV output from my ne555
components from left to right on pic are 1MΩ 0.01uf 1.76kΩ 0.072kΩ or their about Vcc = 9v battery

thanks again

 

[jjw]

Why there is 1Mohm resistor?