ULTRASONIC TRANSDUCERS

[Dingo]

I notice Oatley sell ULTRASONIC TRANSDUCERS pretty cheaply. Is this what you need to give a robot rangefinding abilities?

I mean if I want a robot to know how far something is away from it - is this what I buy?

Is there some really expensive part that I need to use as well?

[ZapBrannigan]

Yes, that would be correct It is an element of basic sonar.
The ultrasonic transducer is a component that creates sound waves. You can send out a ping and then measure the time for the response (filtering on the expected frequency) to determine distance.
If one was quite clever in their circuitry, they could also use it to determine speed of incoming body (based on doppler effect).

Edit: The minimum distance that you can measure is based on the length and frequency of the ping you wish to send out. This is because you may already be receiving an echo before you have finished sending out the ping. Pingtime in seconds x 330 (speed of sound in m/s) = distance in meters that you are blind in.
Lower frequencies are better for distance, but bad for short range determination, and vice versa for high frequency. You need at least a few cycles for the ping so appropriate filtering can be made on incoming sound.

[Dingo]

hmmm interesting, what component do you need to read the returned ping?

[ZapBrannigan]

I *believe* you can use the transducer device itself... I may be wrong, or it could depend on which device you buy.
It has been a while since I was researching sonar

[Dingo]

Oatley do sell a kit titled "parking radar kit" that looks like it uses 2 ultrasonic transducers to send and receive.

It is only $19 ! very tempting.....

[Dingo]

I believe there is a sender unit and a receiver unit.

I have ordered the parking radar kit from Oatley - that was a week ago - God they're slow compared to everything else I mail order on the 'net!

When it arrives I'll examine it and post a description in the project area or here.

[Glenn Visca]

I feel a little embarassed adding this here ... but oh well - lets see what happens.

For the last month or so, I have been researching ways to ascertain water level in my rainwater tank(s).

Thus far, my options have been

1. Visible inspection. Cludgy devices slung on the outside of the tank, dipsticks and the like.

2. Pressure readings. This became a possibility by measuring head pressure. Used in many commercial applications ... but with such low pressures (even though there could be 50,000 litres of water), becomes difficult and when seaching for digital outputs ... becomes costly.

3. Ultrasonics. Took me to a number of commercial sites/suppliers with devices specifically designed for the purposes of about USD$1,000 to USD$1,500. Just a little more than I wanted to spend (by an order of magnitude.)

And hence it is the last one the brings me to this forum. Somehow I managed a lucky google hit onto a robotics site somewhere, and have spent the last couple of days trawling through web sites on what you robotics folks do.

And ... all things being equal, this looks perfect. Accurate enough ... and at the right price.

The depth of my tank is around 7 feet (2.1 metres) and it is a sealed poly tank. I was considering placing the transducers on the top of the tank (above the overflow so they will never get wet), and out of direct weather. Bouce a ping off the surface of the water ... and hence easily calculate water available in the tank (and thus ensuring I dont cook my irrigation pump by running it dry).

I was considering placing the controller in my garage - lets say 15 to 30 feet (cable length) from the transducer, and would be happy for both a LED/LCD output at the controller, or, pick up the measurements from an RS232 (or equiv) feed into something I can write on a PC to pick up the stream off the serial interface.

I have had a look at the BrainStem and OOPic pricing in Australia ... and was wondering if I needed anything quite this complex. Can anyone help here ?

Of course this is offset by the fact the BrainStemp and OOPic controllers appear to have ultrasonic command set (?)

I must confess, I am no electronics whizz ... but I do have 20 years of commercial IT experience ... so I can turn my hand at programming most things without difficulty.

Any assistance / comments / "dont be so bloody stupids...." gladly received here or my email to [e-mail]

Cheers,

Glenn.
Pakenham,
Victoria, Australia

[Dingo]

Hehe, yep I think this is a common problem - I've see others trying to do the same thing. I'm surprised that there isn't a kit out there somewhere for this.

I did build the Oatley kit and have to say it has had mixed results. I may have fried the deleicate internals of the transducers trying to solder them on so I'm not prepared to say it is no good or great until I order another kit and be more careful this time . Unfortunately built as standard it is set for a particular distance (you choose) and it will tell youif something is there or not. Of course, using a microcontroller you could modify this behaviour.

Since then I've seen that Jaycar have an Ultrasonic transducer unit with both the send and receive part for $5. (Search for "Ultrasonic" at www.jaycar.com.au )Of course you then need to driver this unit. For that or the Oatley kit, you need a microcontroller. Also I haven't as yet found a lot of information about it either.

If you haven't used microcontrollers before I highly recommend the PicAxe range. They are cheap, available in Australia and couldn't be simpler. The Aussie distributor is www.microzed.com.au/

They have a BASIC interpreter built into them (into a standard Microchip PIC uC)

The only real drawback for this application is that they aren't as fast as other microcontrollers available but I think they should work.

(BTW I have a list of Aussie suppliers of electronics etc here: www.users.on.net/~symes/links_tree/links.htm

There are other, easier to use but slightly more costly Ultrasonic sensors around, I think most are based on the Polaroid units. They all pretty much need a Microsontroller for this app I think.

If you wanted another fail safe - another thought came to mind, what if you had a basic movement sensor on the output of the pump, and if nothing was coming out, you shut it down straight away. Just another sanity check on the system.

P.S. Maybe something like these relay boards www.futurlec.com.au/TrainingBoardAccessories.jsp might be useful too for output.

Futurlec also have lots of microcontroller boards all pre-built and very cheap for what they are. You might want to check them out. I would recommend something like the Mega32 controller board if you wanted to spend that sort of money www.futurlec.com.au/ATMegaControlBoard.jsp

I have it and find it very good indeed.