Author Topic: Ultrasonic transducer question  (Read 3607 times)

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Offline aruna1Topic starter

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Ultrasonic transducer question
« on: May 18, 2011, 07:00:52 AM »
Hi
I'm working on a ultrasonic transmitter and using transducer pair like in image I attached.

Currently I'm giving 9V (7809) to drive the transducer (TX) through a H-bridge.

My question is;
I have read in internet that these transmitter drums can operate voltages up to 20V and as the voltage increase the transmission distance increases.I don't have any datasheet on the module and it doesn't have any model number or reference.

So is it possible to use a charge pump system to boost 5V supply to 15V and use this 15V to drive the transducer? Since charge pumps cant deliver large current I wonder whether this is possible. But if it possible it will save me from making an inductor based boost converter.

If this is possible what is the maximum ultrasonic burst duration I can achieve with charge pump?

I wonder how they do it on ultrasonic range finder modules like SRF05, they work with 5V.


as I'm using 9V currently I was able to send ultrasonic signal to about 25m. but this is possible only If I'm transmitting continues 40KHz stream.
But if I send 40KHz burst , receiver sometimes failed to grab it even at distance of 8m and receiver is already using gain of 1360.

please note this system is not using the reflected ultrasonic signal. transmitter and receiver are in two different places and used to measure the distance between transmitter and receive.

I want to send a super power ultrasonic burst so my receiver wont miss it at 20m  ;D

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Offline marto

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Re: Ultrasonic transducer question
« Reply #1 on: May 19, 2011, 05:55:17 PM »
Yes it should work with the charge pump system as they don't use a lot of current. However the "how long it will last" question is very specific for something which we have no specs on.

I found when playing round with the scope the other day that the response was very dependent on the frequency which the chirp is sent at, there was a order of magnitude drop off after 45kHz so playing the the frequency might give you better range.

Also might be worth trying it just off a power supply to start with and measuring the current draw if its low enough then build the charge pump circuit.

Steve

Offline TrickyNekro

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Re: Ultrasonic transducer question
« Reply #2 on: May 20, 2011, 02:34:40 AM »
And because I do work with somewhat the same project I know the answer... :-p

Get a nice function generator, get a nice scope, and do a low pass filter, replacing the capacitor with the buzzer....

Most probably, these blighters seem to work as a capacitive load. But also, they are extremely band pass...

So, find the frequency that seem to absorb the most power and take the needed measurements to see what their capacitance is.
Though that may not be one... Mine did absorb at 40kHz and 50kHz... Though the absorbing rate at 50kHz was significantly less, don't
let it fool you. Best is to refer to the datasheets about their oscillation frequency. Still, if that's not available, do the above.

My beepers have a capacitive load of 4nF, for example. So running them at 40kHz needs a what to oscillate...
Yeah, you guessed it... It needs a coil!!!! 4mH for the above I have.
Also, it would be much much better if you where to drive it with a sine wave, rather than a square.
Apply a square wave and see what happens. (And yes, what you see is mechanical noise in the beeper, which is not recommended)

Yours seem identical to mine... But I wouldn't count on that, to judge on their load behavior.

So you simply use a in-series RLC circuit, to get some serious voltage kicking in.
Also, it would be very good to calculate the Q factor, cause you don't want to drive them with huge voltages.
And when I say huge, I mean it... An in-series RLC can reach as much as 60V across the cap and the coil, even if you use an H-bridge at 5V...
Theoretically, when in oscillation frequency, the voltage across the components can become infinite. But as components have self resistance, than can't be done.

Anyhow, I have something else in mind also, but first I need to confirm it. So. Wait for my next reply, by tomorrow, it'll be sure, that I would have learned.

Best Regards, Lefteris
Greece
For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

Cheers!

Offline aruna1Topic starter

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Re: Ultrasonic transducer question
« Reply #3 on: May 20, 2011, 12:22:33 PM »
Quote
And because I do work with somewhat the same project I know the answer... :-p

My project is localization system using ultrasonics

Quote
My beepers have a capacitive load of 4nF, for example. So running them at 40kHz needs a what to oscillate...
Yeah, you guessed it... It needs a coil!!!! 4mH for the above I have.

I measured capacitance and its 2.68nF so i guess t requires 5.91mH inductor


Quote
Also, it would be much much better if you where to drive it with a sine wave, rather than a square.
Apply a square wave and see what happens. (And yes, what you see is mechanical noise in the beeper, which is not recommended)

well i guess i can convert 40KHz  square wave to 40 khz sine wave using low pass filter (2-3 active)
problem is I'm thinking of using H-bridge IC like L293 to rive this instead of transistor h bridge (IC makes life easier) I dont think it will accept analog voltage

Quote
So you simply use a in-series RLC circuit, to get some serious voltage kicking in.
Also, it would be very good to calculate the Q factor, cause you don't want to drive them with huge voltages.
And when I say huge, I mean it... An in-series RLC can reach as much as 60V across the cap and the coil, even if you use an H-bridge at 5V...

you mean something like attached image? how to calculate R?

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Offline deladriere

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Re: Ultrasonic transducer question
« Reply #4 on: June 25, 2012, 03:07:01 AM »

I have a similar problem : using an L298N to drive a transducer  at 40 kHz and I also need to transform the square wave into a sine to be able to get the max power out of it by applying a greater voltage
did you find the solution to your problem ?
Can you explain the RLC circuit I have to add ?

Offline aruna1Topic starter

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Re: Ultrasonic transducer question
« Reply #5 on: June 25, 2012, 04:09:30 AM »
hi
i believe  you cannot use L298 as it's maximum frequency is 40kHz, that means you should use it with less than 40kHz signal.
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Offline suvidha

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Re: Ultrasonic transducer question
« Reply #6 on: June 25, 2012, 07:34:40 AM »
hey
m a beginner in robotics and i need help to build an ultrasonic robot..that follows sound.
Please please help me with the schematic using AT89S52 and the procedure to calculate range and position of the object

i saw this post and i think u might  be able to help.

Offline deladriere

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Re: Ultrasonic transducer question
« Reply #7 on: June 26, 2012, 05:46:11 AM »
Hi Aruna 1
The L298N works fine at 40kHz  !
(I use this break board : http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&_trksid=p4340.l2557&rt=nc&nma=true&item=261002237340&si=J71742/X4DggjOvcg9RhoxU3LWE=&viewitem=&sspagename=ADME:L:OC:BE:3160&orig_cvip=true&rt=nc#ht_6815wt_1324

But ready to use another one if necessary : my objective is to get the max signal to the transducer
How Did you achieved that ?

Offline TrickyNekro

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Re: Ultrasonic transducer question
« Reply #8 on: June 27, 2012, 08:36:23 AM »
Thatīs a very old topic but Iīll reply anyhow, just so that the info exists.
Current is not really a problem to use the L298, itīs much unneeded.

Quote
So you simply use a in-series RLC circuit, to get some serious voltage kicking in.
Also, it would be very good to calculate the Q factor, cause you don't want to drive them with huge voltages.
And when I say huge, I mean it... An in-series RLC can reach as much as 60V across the cap and the coil, even if you use an H-bridge at 5V...

you mean something like attached image? how to calculate R?

From what I remember I used a series circuit. Itīs must be more than a year that I started the project and
to tell the truth never ended it, cause I needed to find better transducers and some other things also.

You put the LC in parallel, that creates a band cut filter, you want a band pass filter. The very reason you are using
a coil is to avoid having greater voltage rails in the circuit. The LC circuit itself can create large voltages, it depends
on the quality factor of the oscillation. Since you have fixed capacitance, you also are limited by the inductance selection.
Still the quality factor should be good enough to produce voltages up to 40 - 50V. Of course that would be catastrophic
for the piezoelectric element. So you place a resistor to lower the quality factor of the oscillation, to a voltage around
20V which can be handled by the transducer. I canīt remember the exact formulas to calculate this, but a Google search
should do it, so no worries. Basically what you do is to dump energy into the resistor. But that also means that youīll need
more time to reach full oscillation amplitude. It a trade off. Of course you could temper a little with the inductor value, but
since of the nature of the inductors having about 10% - 20% tolerances, ehhh, I donīt like the solution. Of course, it
would be almost impossible to find an inductor at the exact value you want, so you may start thinking making your own.
There are coil calculators in the internet, free and good onces also, so no worries. You just need to find the core material,
ferrite preferably. All the other usually used materials are not good to these frequencies. (I canīt remember for iron powder but
iron cores are really NO go). Be careful of that.

Also if you are going to use the LC circuit you donīt really need an H-Bridge. You can use one but you can do it with only a
typical push-pull circuit with the other end of the circuit tied to ground. That saves you from other troubles also. There are
many things to consider generally...

But do you want a dirt cheap solution that works and doesnīt need a higher power rail, just 5V ???
MAX232.... problem solved. It has a charge pump, it can drive the load with no problem, itīs not the best of the best
but it works, and much much easier than the coil solution. And itīs much easier to do other things with the transducers,
with little effort like FM and stuff like that... Itīs a dirt cheap solution, I know, but it works great.

For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

Cheers!

Offline Soeren

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Re: Ultrasonic transducer question
« Reply #9 on: June 28, 2012, 03:57:32 AM »
Hi,

please note this system is not using the reflected ultrasonic signal. transmitter and receiver are in two different places and used to measure the distance between transmitter and receive.

I want to send a super power ultrasonic burst so my receiver wont miss it at 20m  ;D


Why didn't you just keep to your old thread?

I believe I already gave you a solution there, more than a year back:
http://www.societyofrobots.com/robotforum/index.php?topic=13570.msg100346#msg100346'
All you need to make strong pings from 5V is a BC337 and a coil (or make it a transformer by adding a winding for a huge boost).

How you're gonna get the distance without TX and RX synchronized?
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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