[aprssig] FEMA- Flood gauges (feedback)

Ross Whenmouth ross at topwire.co.nz
Fri Sep 16 17:53:52 CDT 2016

Curt Mills wrote:
> Saw this idea some years back, probably on this same sig:  Ultrasonic 
> transducer pointed down a plastic pipe from the top. No moving parts. 
> These days you could probably run it with a tiny Arduino or an Rpi 
> with no trouble.
A while ago, I was given a cheap and nasty "ultrasonic tape measure" - 
it uses an ATmega16 processor to generate the TX pulses and time the 
delay for the RX pulses, and it seems to work ok. So, yes, an Arduino 
(ATmega328 processor etc) should be suitable (it could be the APRS 
TNC/modem as well) but I think that you might need to do something about 
the standby quiescent current draw of the LDO regulator on the Arduino 
board. An Rpi would use far more power than an ATmega328 that spends 
most of its time sleeping (~ 0.75 uA sleeping with the 32kHz RTC running 
vs hundreds of mA for a Rpi).

One question I have about an ultrasonic level gauge is, will it misread 
the water level as high if a spider decides to make its home in the tube 
(complete with cob web, the remains of its victims and bundles of spider 

Robert Bruninga wrote:
> The indicated float switch is completely sealed and has an internal magnetic
> reed switch.  As long as the float moves, it will work.  But I guess you are
> suggesting the sliding surface on which it slides could become fouled...
> hummh..
Yes. The more dirty the water is (flood waters?), the more likely the 
moving parts of the float switch are to foul up and jam. I was also 
thinking that a length of insulated ribbon cable would be cheaper than 
multiple float switches and should give a more precise level indication 
(eg inches of water instead of low, medium or high level switch).

Ross Whenmouth

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