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 Circuit to drive a LED Display

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ImDave Posted - May 31 2010 : 6:00:12 PM
Hi,

I want to make a wind speed meter that shows the current wind speed and the fastest since resetting.

I looked online and simple meters are $150+ which is nuts for a $10 spinner, reed switch, a small magnet and a handful of components. I have the hardware all working fine, now I just need to be able to do the read out.

I have a bunch of these I took of an old display.

http://www.allelectronics.com/make-a-store/item/TDA-6910/DUAL-7-SEGMENT-LED-DISPLAY/1.html

Anyone know of a basic schematic to
Count pulses from the reed switch and magnet.
Display the speed.
Allow adjustment for square wave from reed switch to calibrate the thing.
Store the highest speed reached.
Allow reset.

Thanks

Dave
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Aaron Cake Posted - Jun 01 2010 : 11:08:32 AM
The circuit is fairly simple up until the requirement to store the highest speed. Until then, all you need is a frequency to voltage converter (there are ICs for this purpose) and then a simple LCD panel voltmeter or LED voltmeter circuit.

Instead of using a reed switch, use a variable reluctor (wrap a magnet with a coil of wire and have a piece of metal sweep by or use metal fan blades) or a hall sensor.

Since you need to store the peak, you can either use an LCD panel voltmeter with peak and hold capability, or dump the frequency to voltage and just use a microcontroller. In the case of the microcontroller, there is very little circuit for you to build as it is all done in software.

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