Ultrasonic.....once more

[mcs51mc]

Hi there, I'm trying to get an US transimtter/receiver to work ... ...
Circuit for both T&R are something I grabbed from the net except that I power the LM311 with 24Vdc instead of 5Vdc or 9Vdc.
Why? Because my transmitter is a complete sealed one MA40E7 from muRATA.
Datasheet here: **broken link removed**

Questions:
They talk about 100Vp-p, so how do I make 80 to 100V pulse from a 5V one?

The 40kHz frequency, how accurate does it need to be?
The signal generated by the µC is 41.66kHz is that ok?


Thanks for any reaction

 

[Nigel Goodwin]

Questions:
They talk about 100Vp-p, so how do I make 80 to 100V pulse from a 5V one?

It's designed to be fed from a transformer.

The 40kHz frequency, how accurate does it need to be?
The signal generated by the µC is 41.66kHz is that ok?

You should tune the frequency for maximum output from the tranducer, they are quite critical about the frequency - really it's essential to make them adjustable.

 

[mcs51mc]

Hi Nigel,
When you said "transformer" I first thought you're kidding me

Then I search the net for US with transformer and found one circuit at www.ednmag.com

I made the circuit in the attached file, search for an audio transformer in my over-aged stuff and found a small transformer, not greater than 1.5cm³
Primary winding = 44.5R (with middle tap 23.6 and 24.2R)
Secundary winding = 3.7R
Is this valid data for an audio transformer ?

First part of 556 makes 40kHz signal
Second part makes signal 100ms high / 1ms low
Gates from 4093 combine both signals to 1ms with 40kHz burst every 100ms.

Gates from 4049 makes, or better, are supposed, to drive the transformer so that I have .... Vac for the transmitter.

Since I measure Ohmic values on boh sides I suppose it's a good (audio) transformer.

Can you please tell me what I am supposed to measure at the secundary side of the transformer because I measure nothing with a scoop.

 

[Hero999]

He's not joking, a transformer is exactly what you need.

An mains transformer is no good because it's designed to work at 50/60Hz and an audio transformer is no good either because it's designed to work at 20kHz at best.

You need to wind your own transformer. Select a core suitable for the frequency and power level and wind the right number of turns on the primary and secondary.

You need a ferrite core (used for switched mode power supplies).

How much power does the piezo require?

The chances are your CMOS IC won't be powerful enough to drive it, power MOSFETs are probably your best bet.

 

[mcs51mc]

How much power? Don't know, nothing to find with "W" unit in the datasheet or even on the muRata web site

For some reason I can't upload the datasheet

Why is it that 99.99% of the circuits on the web don't need all that high power stuff (transformer, mosfet, ...) ??

 

[dknguyen]

Why is it that 99.99% of the circuits on the web don't need all that high power stuff (transformer, mosfet, ...) ??

Because you aren't looking for them.

 

[Hero999]

It depends on the piezo, not all transducers require that higher voltage, some work at lower voltages.

Your 100V unit will work at 10Vp-p but it won't be as powerful.

If you can't find it on the datasheet, you need to ask their technical department what the impedance is at 40kHz, then you can easilly calculate the current draw and figure out what transformer you need.

Note that 100Vp-p means 100V peak to peak or 50V peak, therefore if you want to drive it at 48V peak and you're using a 24V suppliy with an h-bridge driver, you'll need a transformer with a turns ratio of 1:2 to double the voltage.

 

[dknguyen]

Check out www.senscomp.com. They sell little transformers that can step up 5V to 100Vpp and other ultrasonic components.

You need 100Vpp? It's an electrostatic (rather than a dead-easy to use piezo right?) If so then it also needs a ~100V DC bias. I'm not sure how you can apply a 100V bias from a 5V source with the transformer though. I've been trying to figure that out myself. I think their reference circuit for one of their ICs. has something about a diode and capacitor on the high voltage side that can do it, but am unsure.

 

[Hero999]

You use a small DC-DC converter to generate 100V bias from 5V right?

However, the infromation on the website says 100Vp-p which only makes sense for AC voltage not DC.

 

[dknguyen]

You use a small DC-DC converter to generate 100V bias from 5V right?

However, the infromation on the website says 100Vp-p which only makes sense for AC voltage not DC.

THose converters are hard to find. I remember seeing one a long time ago. But haven't been able to find one since.

 

[Hero999]

You can build one yourself quite easy.

 

[philba]

one easy approach is to use a max232 or clone to drive the transmitter. You'll get around 25V P-P which is a sight better than 5 and it's pretty cheap and easy to do.