Dennis Plunkett wrote:

> >Hmm.  Never thought of peak frequency measurement.  I'd simply bounce a
> >pulse down the tube and recognise the peak return.  Time for the bounce
> >is distance.

This would impose a resolution constraint on the measurement.If I check the peak amplitude (in the
current as suggested by
Clyde, or the output voltage envelope of an electret microphone),
I think the resolution constraint only comes in when measuring the
amplitude, not in the actual distance  What do you think?.

Dennis Plunkett also wrote


> Firstly I am assuming that the range you are after is 2.5m, not a change
> from x to x + 2.5m

It actually would be for a change. Total range I'd like would besomething like 3m

> Ah, it all sounds so simple! There have been many attempts to derive an
> ultrasonic depth gauge, most do work, however the current drain is high. You
> may wish to look at the ones made by Kodak. As for your idea of a plastic
> pipe and speaker, yeah, it will work but with vary limited success due to
> variations in temperature, atmospheric temperature drumming in the pipe due
> to wind and other general activities on the water eg boating, yet alone the
> problems that you will have with keeping the pipe inlet unclogged and wave
> action.

I'd make the hole right at the bottom, with a 1mm breathing holeat the top to reduce wave effect. I
can guarantee that no person
with anything between his ears would attemp any watersports on
this particular river. The bottom is probably 50% rocks and
boulders, with the water level changing at a tens of centimeters/hour.


> If the money is coming out of your own pocket, then you may wish to look at
> other methods. The first question is do you have mains power, if so then a
> simple float on a cheep optical encoder will do the job (You can purchase
> quadrature shaft encoders, but they need a well or bubbler system to

Wilt this work over a 2.5m range?

> operate). If you want to have more fun, then look at a silicon strain gauge
> that Motorola make, with this you could make a vented differential pressure
> transducer

Hmm. This could be a good starting point.

> (Hint hint for the barometric one, note that there are some cheep
> voltage type sensors here that you could use to and mount directly on a
> PCB!).

Who makes these?

>  Effectively you are after a whether station, if you have the bucks to spend,
> then look for "ALERT" equipment on the WEB (Around $3000, and it will log
> the data to, only some not all!), this is the cheapest form of remote radio
> based stuff (Will also measure rainfall (Bonus)). Other than that there are
> a few companies that make the sensors and data loggers that you're after try
> Unidata

Ha! with you guys ruining our rand value, $3000 is way, way,way out of my reach!


Clyde Smith-Stubbs wrote:

> Use a pressure sensor with a pipe going to the bottom of the river. I've
> got this set up with some water tanks - still some calibration issues, but
> the basic concept works well, and there is no electronics in the water.
> You do need an air pump to purge the tube. An alternative would be

> an absolute pressure sensor encapsulated and dropped to the bottom
> and referenced against a similar sensor in air.

If they aren't too expensive, I can get the barometric pressure fromthe dry one. What do they go
for?

> This might work, but it sounds a little touchy to set up to me. You
> could probably measure the speaker impedance rather than using a
> microphone.
>
> > BTW what sort of a sensor would be able to measure
> > barometric pressure? I am going to pay for this, so it
>
> Honeywell have small pressure sensors - they're not too expensive. They
> are a bridge setup with a diaphragm and strain gauges, excited with 5-10V
> and output is differential, in the mV range.

Thanks for your inputs

--
Friendly Regards

Tjaart van der Walt
mailto:tjaart@wasp.co.za

Add your voice !!
Vote at the Great G Com Public Vote. Go to :
http://www.wasp.co.za/~tjaart/gcomvote.html

|--------------------------------------------------|
|                WASP International                |
|R&D Engineer : GSM peripheral services development|
|--------------------------------------------------|
|SMS mailto: 0832123443@wasp.co.za  (160 chars max)|
|     http://www.wasp.co.za/~tjaart/index.html     |
|Voice: +27-(0)11-622-8686  Fax: +27-(0)11-622-8973|
|          WGS-84 : 26¡10.52'S 28¡06.19'E          |
|--------------------------------------------------|