How to generate 150Vpp/40kHz signal for Intermediate Frequency for Ultrasonic sensor?

[chirag2239]

Hello,

I am in a very big problem.

I have attached an Image that provides the details of my Ultrasonic Transducer.
I have an Ultrasonic sensor that operates on 40Khz 150Vpp frequency. I am having all the things ready. The suppliers and manufacturer told that it will require 150Vpp/40kHz signal as a carrier frequency. For that the IFT (Intermediate Frequency transformer) of 6.8mH will be used.

I do not know how to generate the 150Vpp 40kHz signal and how to get out from this problem.

I need some help for solving this issue. Schematic to generate such output will be the best. But solution are welcome.

Please help me.

Thanks.
Chirag

 

[betwixt]

Before answering we need to know what your application is. Some ultrasonics use a transmitter with continuous drive voltage and some need pulses, for example in range finding units. The way it is driven is quite different from one purpose to another.

The data sheet shows 2000pF capacitance and you have been advised to use a 6.8mH inductor (not an IFT though !) so the natural resonance of the transducer and inductor in parallel will be about 43KHz which is reasonable. You probably want slightly less inductance or a variable one to optimize efficiency, 7.9mH would probably be better but it depends on the driver circuit to some extent.

Brian.

 

[FvM]

It's wrong to say that the transducer "requires 150Vpp" drive signal. The specification is a maximum rating "allowable input voltage". Most applications use a lower drive level.

As betwixt mentioned, we have to look at the application requirements to understand what's an appropriate drive level. Similarly a reasonable matching circuit depends strongly on the application parameters. E.g. if the sensor is operated with pulses respectively bursts, the matching circuit should achieve low Q for best time resolution.

 

[Warpspeed]

These transducers all rely on some kind of electro mechanical resonance, and the frequency tuning is very sharp. If you drive it slightly off frequency the acoustic output will fall off very quickly.

So really, there are several quite different approaches, shock it into ringing with a sharp single pulse.
Blast it with a short burst of cycles at 40 Khz and hope it will resonate reasonably well.
Or make the transducer itself part of an oscillator so it finds its own self resonant frequency. Pretty much like a high power crystal (or ceramic resonator) oscillator.
This will give the highest acoustic output for the lowest power.

And not mentioned on the data sheet, but you can use the series resonance point that has a fairly low drive impedance, and requires a much lower drive voltage.

 

[chirag2239]

These transducers all rely on some kind of electro mechanical resonance, and the frequency tuning is very sharp. If you drive it slightly off frequency the acoustic output will fall off very quickly.

So really, there are several quite different approaches, shock it into ringing with a sharp single pulse.
Blast it with a short burst of cycles at 40 Khz and hope it will resonate reasonably well.
Or make the transducer itself part of an oscillator so it finds its own self resonant frequency. Pretty much like a high power crystal (or ceramic resonator) oscillator.
This will give the highest acoustic output for the lowest power.

And not mentioned on the data sheet, but you can use the series resonance point that has a fairly low drive impedance, and requires a much lower drive voltage.

Thanks for the reply. I am new to this kind of Ultrasonic sensors. Yes, I am using Ultrasonic sensor for Range finding application. After your reply I got confused more. As you have said that I need IFT for resonance. So I am generating the frequency of 40kHz from this capacitor and inductor unit. Am I right?

I am using ATmega8 for generating pulses of 40kHz. Do I really need this MCU for generating pulses as I am using IFT and Capacitor for resonance?

My next question is that how do I have the 140Vpp voltage at output? Yes, 40kHz is got,then what about 140Vpp?

I am confused that, if I will use IFT and capacitor, then I am having a kind of oscillator. so I will have 40kHz frequency at output by tuning them properly. So I can easily eliminate the Microcontroller if my understanding is right. This is quite make sense but what about the 140Vpp 40kHz? AS I am using 5V battery to supply ultrasonic sensor, then how can I get the 140Vpp? My Ultrasonic sensor has only 2 pins, so where I should apply the signal and where I can apply the supply voltage? This is a single transceiver so transmission and reception is done by single unit.

Really very confused. Can you provide a simple drawing to understand all these mess along with this question's answer?

Thanks.
Chirag

 

[FvM]

I suggest a different approach. Try to get hold of known working 40 kHz rage finder schematics and study their operation.

 

[KlausST]

Hi,

Schematic to generate such output will be the best

Can you provide a simple drawing to understand all these mess along with this question's answer?

Usually the OP should provide informatins what and how he wants to achieve.
What he did so far, what internet research he did, what documents he refers to.
(Otherwise it seems he is too lazy to search for informations himself, and just let others do the job)

I assume there are a lot of informations around how ultrasonic range finding works. With calculation examples, with signal flow charts, maybe even with schematics...

Klaus

 

[chirag2239]

It's wrong to say that the transducer "requires 150Vpp" drive signal. The specification is a maximum rating "allowable input voltage". Most applications use a lower drive level.

As betwixt mentioned, we have to look at the application requirements to understand what's an appropriate drive level. Similarly a reasonable matching circuit depends strongly on the application parameters. E.g. if the sensor is operated with pulses respectively bursts, the matching circuit should achieve low Q for best time resolution.

Please refer this PDF. You will get all the info there. https://www.futurlec.com/USTR40-14A.shtml

Thanks.
Chirag

 

[betwixt]

The data sheet expalins how to do it. The term "IFT" has other meanings, it is really just a step-up transformer.

What we had to find out was what it was used for and how it was used. Some ultrasonic systems send a continuous signal and use an independant microphone to pick it up, typically these are used in motion sensing where a change in the level or phase of the signal tells you something is moving within the sound path.

Your design uses one ultrasonic sensor to do the sending and receiving and it times how long it takes for a burst of sound to return back to the transducer (the echo). That means you have to alternate between sending a tone and listening for it's return, that's why bursts are used, on means send, off means listen. If you follow the schematic on the data sheet it should work, your MCU has to provide a few cycles of 40KHz, repeated at a slow rate, maybe once per second. The MCU signal turns the transistor on and off which in turn makes a high voltage appear across the secondary of the transformer. With the optimal transformer, having approximately 8mH secondary inductance, it will resonate with the 2,000pF capacitance of the transducer and produce the signal you need. The MCU has to produce enough pulses at 40KHz to 'pump' the resonant circuit to full power, I'm not sure how many pulses would be needed as it would depend on the 'Q' of the tuned circuit and how much load the transducer places on it but I would guess probably 50 cycles or so would be adequate. You really need to use an oscilloscope to look at the waveform and adjust the number of pulses so it was no more than necessary to achieve full output.

When you have found the optimal transmission signal to use, all you do is send one burst, then time how long it takes for the amplifier to see the echo. The "time of flight" can be converted to distance fairly accurately. You can impove the accuracy if needed by taking into account the humidity an temperature along the path you are measuring as both of these have an influence on the speed the sound travels in air.

Brian.

 

[chirag2239]

Thanks Betwixt..!! It did make sense. Whenever I will find any difficulties, I will be back here to ask for your help.

 

[chirag2239]

Thanks Betwixt..!! It did make sense. Whenever I will find any difficulties, I will be back here to ask for your help.

Hello guys,

I am confused that here the capacitance of 2000pF is mentioned so do I need to connect the capacitor too? If yes, then in parallel or series? I have tried but I did not get the 150Vpp 40kHz signal at output. So what is the problem?

 

[betwixt]

The 2,000pF is the capacitance of the transducer (1,800pF +/- 15%) and surrounding parasitic capacitances so you do not need to add it yourself. However, given the large component tolerances it might be a good idea to either make the inductor variable and/or make provision for adding additional capacitance to peak the tuning at 40KHz.

In a circuit where you are exciting it at a constant frequency (from your MCU), you ideally want the inductor and capacitance of the transducer to resonate at the same frequency so you get most voltage generated. This is why some circuits use them as part of the oscillator circuit itself so they decide the frequency whatever the exact inductance and capacitance may be. In your application that wouldn't be an option though.

Brian.