ultrasonic transmitter circuit question

[aruna1]

Hi
I'm making a ultrasonic transmitter and receiver pair.
this is not for obstacle avoidance.I use it for measure distance between tx and rx units.

so my question is how to increase the transmission distance?

for IR transmitters increasing the current through IR LED increases its transmission distance.what I need to know is what parameters affect transmission distance of ultrasonic?

I read some articles and posts in internet and some of them has H bridge(send current in both directions) to control the TX transducer


and in some circuits transducer is only fed with signal with respect to ground (send current in single direction)


I have attached similar circuits found on internet to clarify what I'm saying.

So what are the advantages of each method and what is the best method to increase the range?

I have some more questions about receiver side but I guess I need to clarify questions about transmitter side first
thank you

[Soeren]

Hi,

so my question is how to increase the transmission distance?

for IR transmitters increasing the current through IR LED increases its transmission distance.what I need to know is what parameters affect transmission distance of ultrasonic?

US X-ducers are high impedance, so you concentrate on the voltage instead.
US behaves just like audible sound from a speaker (or a piezo much like the USTX) in that respect, so, the more you get the membrane to flex back and forth, the higher the SPL and the longer it will travel.

So what are the advantages of each method and what is the best method to increase the range?

The H-bridge will make the membrane flex double the distance (and so should have a range that's about 1.4 times a unipolar drive), but at the cost of a bit more complexity.

Another way to increase the range is to use the X-ducer in an LC resonance circuit, where the drive voltage could potentially reach a few hundred volts.

A lot of range can be won from careful receiver design as well.

[aruna1]

Hi soren

I dont know what type of transducer I have now. I mean there is no model number r anythng on it.
transducer I have is similar to this. on receiver letter "R" is marked and on transmitter letter "T" is marked. and in both transducers one pin is marked with lack.

[Soeren]

Hi,

I dont know what type of transducer I have now.

Perhaps the place you got them from know, but the main info needed to use them is the peak frequency and the max. voltage/power they can handle.
The frequency can be found reasonably easy, but they're probably 40kHz (are you sure the writing on them doesn't include eg. 25 or 40, as in 40T or T40?), but finding the max. voltage would be destructive opf course.
Usually they're pretty robust and you could find a datasheet from some that have the same size. The innards is very close to a piezo disc so they won't differ much between similar diameters types.

Do you have access to a capacity meter?

[...] in both transducers one pin is marked with lack.

"Lack"?
You mean "black", or is one pin missing?

[aruna1]

hi soren

well doing electronic sucks in sri lanka. thing is you cant get parts like tansducers ,LEDs etc by part number.they simply dont know. onl ICs and transistors can be brought with part number 
for ultrasonic trasducer all we can do is ask "I want to buy ultrasonic transmitter and receiver pair" and sales man will give you two drums. no part number or anything.they even dont know the part numbers.If you ask what is the part number of this they say "they dont come with part number"


only marking is letter "R" and "T"

and my bad for spelling mistake its not "lack" it should be "black" --> one pin is marked with black circle.

and ya I have access to a capacitance meter.

[Soeren]

Hi,

[...] for ultrasonic trasducer all we can do is ask "I want to buy ultrasonic transmitter and receiver pair" and sales man will give you two drums. no part number or anything.they even dont know the part numbers.If you ask what is the part number of this they say "they dont come with part number"

Sounds like there has gone "Radio Shack" in electronics dealers world wide 

and my bad for spelling mistake its not "lack" it should be "black" --> one pin is marked with black circle.

OK, then at least you have that reference - it's probably connected to the aluminum housing.

and ya I have access to a capacitance meter.

Great. Then measure the capacity of both transducers.
If the cap meter have more than one frequency range, use the range closest to 40kHz.
Knowing the capacitance will make it easier to make a resonance circuit at the right frequency.

BTW. Don't put DC on them, it will weaken (or even destroy) them.

[aruna1]

Great. Then measure the capacity of both transducers.
If the cap meter have more than one frequency range, use the range closest to 40kHz.
Knowing the capacitance will make it easier to make a resonance circuit at the right frequency.

BTW. Don't put DC on them, it will weaken (or even destroy) them.

ahh frequency in capacitance meter?
anyway I have frequency meter also.

and i made the circuits (RX & TX) on a two protoboards with 40kHz signal and is working for distance about 8m. although receiver side gain is about 570.
I'm worried about having large gain, because it will ruin the purpose of measuring distance between transmitter and receiver because it will pick multi path propagated signals. even though I haven't put this in to test. any suggestions on this?