ultrasonic transducers

[geir102]

I’m planning to use ultrasonic transducers for a small project. But I’m wondering is it really as easy as applying 5V and GND to the transmitter, to make the signal. I can't find a datasheet.

Then using a opamp to amplify the signal from the receiver and straight in to the µC.

[adafruit_support_bill]

The Maxbotix ultrasonic rangefinders in the store are pretty simple to use: Just apply 5v & GND and read 0-5v on the analog pin. Pulse-width and serial outputs are also available.

The data sheet is here:http://maxbotix.com/uploads/LV-MaxSonar-EZ1-Datasheet.pdf
An example application is here: http://www.ladyada.net/make/pumpkin/pumpkin.html

[geir102]

Thanks but I'm not building a range finder. The receiver and transmitter is not even part of the same circuit. I'm asking about the transducer

[adafruit_support_bill]

What transducer are you planning to use?

[geir102]

I was planning to desolder them from a device like this one, http://letsmakerobots.com/node/14356.

Just to make a quick prototype

[adafruit_support_bill]

Not familar with those. But if you are working with a raw transducer, you will need to generate the ultrasonic signal yourself. Most are just simple piezo elements with a low-mass diaphragm.

[philba]

No, it's not as simple as applying power. I'm sure you are familiar with the theory - send out a sound, listen for the echo, measure time and that defines the distance. Lots of details though.

The transducer needs to be driven at it's resonant frequency - typically 40Khz but there are lots of other frequencies. Since it's trying to produce an echo, returned energy is proportional to transmitted energy (everything else held constant). Thus, you want to transmit as much power as possible. You really can't drive the transducer from a 5V (or 3.3V) pin and expect much of an echo. Most transducers that I have looked at can take 30-40VDC so some sort of booster is needed if you want real "punch". One clever design uses a max232 to increase the voltage (and thus the power).

The echo, even with a powerful transmitter, is fairly faint and needs amplification. Typical gains applied are 40-100X. You'll need an opamp that can do this at 40Khz (or what ever frequency). So, pick one with the right gain at your frequency.

If you look at the maxbotix datasheet, they have a schematic that may get you started. iirc, it doesn't have enough detail to build one but should at least point you in the right direction.

[geir102]

Perfect answer, thanks Do you also know if I need AC or DC on the resonance frequency. I mean can I use a pwm signal and a simple circuit with a FET or do I need some sort of an H-bride

[philba]

You could get by with just a pulse stream but an HBridge or push-pull circuit will increase the radiated power. If you have a higher voltage source then just using a transistor as a switch (don't really need a mosfet) may be sufficient. The nice thing about the max232 approach is that is gives you + and - voltage (around +10 to -10, iirc). A simple pulse stream is all it needs.

Also, if you look at the maxbotix approach they use a small transformer and push-pull it with 2 output pins.

I suggest you try the simplest approach first. If it works, declare victory.

[geir102]

Great thanks a bunch