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### Author Topic: Ultrasonic Sensor diagram  (Read 3404 times)

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#### The Big B

• Jr. Member
• Posts: 25
##### Ultrasonic Sensor diagram
« on: June 10, 2010, 01:59:53 PM »
I'm just looking for a little advice on making an ultrasonic range finder. I have the components to make the sensor on this page http://www.micro-examples.com/public/microex-navig/doc/090-ultrasonic-ranger.html however this design seems to be quite complicated compared to the IR sensors I have made before. What I want to know is if anyone who may have built one before can tell me if this is an over complicated design or is this the way to go?

#### waltr

• Supreme Robot
• Posts: 1,944
##### Re: Ultrasonic Sensor diagram
« Reply #1 on: June 10, 2010, 03:13:40 PM »
Quote
can tell me if this is an over complicated design

That is a very simple design and I don't think it could get any simpler than that.

Do some more searches for US range finders to understand what is required for them to work well. It's not as easy as IR.

#### Soeren

• Supreme Robot
• Posts: 4,672
##### Re: Ultrasonic Sensor diagram
« Reply #2 on: June 10, 2010, 05:32:22 PM »
Hi,

It's bordering on too simple, but since he only claims a range of 2m, I think it should work.

One thing to pay extra attention to, is the resonance circuit made up by L1 and SP1 (the US transmitter piezo).
This has to be at resonance at the frequency used (f_res=40kHz) and since different transducers will have different capacity (could be from say 5nF or less to 100nF or more), the value of the coil (mentioned as 330µH) will have to be adapted - or the frequency can be changed (within reason) to maximize the amplitude over the transducer.

To be in resonance (at 40kHz) with the 330µH inductor, the capacity of the transducer must be 48nF (0.048µF). Half the capacity needs twice the inductance and v.v. to keep f_res at 40 kHz

The more you change f_res from the natural mechanical resonance (and hence optimum sensitivity) of the piezo electric quarz crystal, which is the active element in a US sensor, the less sensitive it will be.
The more you move the f_res away from the frequency of the transmitters oscillator, the less amplitude (voltage) you will put on the transmitter crystal.

If you have a datasheet on the US pair, post a link to it and the frequency and value of inductor needed should be easy to find.
Regards,
Søren

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

#### The Big B

• Jr. Member
• Posts: 25
##### Re: Ultrasonic Sensor diagram
« Reply #3 on: June 11, 2010, 07:15:34 AM »
Ha and there was me thinking it seemed complicated, my bad, thanks for letting me know!

Here is a link to the transmitter http://ie.farnell.com/prowave/400st160/transmitter-ultrasonic-40khz-16mm/dp/1007332?Ntt=100-7332

Looks like the capacitance is way lower than what you were saying is needed, any suggestions on what is best to do or if it would still work?

#### paulstreats

• Supreme Robot
• Posts: 1,381
##### Re: Ultrasonic Sensor diagram
« Reply #4 on: June 11, 2010, 11:15:17 AM »
Hi,

Just for reference. There are many Ultrasound Rangefinders that are already constructed and include simple communication protocols for controlling and reading them. They are a little more expensive than the individual components, but hey they are readily built and ready to go.

http://www.sparkfun.com/commerce/categories.php?c=84
http://www.active-robots.com/products/sensors/sensors-devantech.shtml

#### Soeren

• Supreme Robot
• Posts: 4,672
##### Re: Ultrasonic Sensor diagram
« Reply #5 on: June 11, 2010, 05:24:10 PM »
Hi,

Looks like the capacitance is way lower than what you were saying is needed, any suggestions on what is best to do or if it would still work?
It wouldn't work with 330µH.
As I mentioned, you have to scale it and since the capacitance is 20 times smaller, the inductance have to be 20 times higher, to keep f_res the same. With an inductance of 6.6mH you stay at 40kHz with this US TX/RX pair.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?