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Author Topic: Need help with analogue charge meter design  (Read 1837 times)
United States United States


Maximilian Libra
« on: May 13, 2010, 05:35:08 pm »

What I need is a small analogue meter that can read a charge as it builds up. The charge would be a relatively small amount, specifically the amount needed to execute a camera flash, but instead of a light turning on to let me know it's ready, I want a meter to show the charge building up till it's ready. This will require a few things:

* a small analogue meter to read the capacitor charge off the flash (I'm assuming it uses a capacitor). That is to say, a moving needle, rather than a series of lights or digital readout. Preferably round, like a steam-gauge, but not required. The key requirement is that it be no larger than an inch or two in size.
* the ability to calibrate said meter to follow the charge from zero to "fully charged" state, without wasting its range on higher charge ranges that won't get used. For instance, I don't want the needle on the meter to be stuck with a range of 1-100 when the highest charge I'll ever attain is a 10 (or whatever arbitrary numbers are assigned). The reason I want to limit the range is so that the needle will move slowly across the span as the capacitor gains charge, rather than only a fraction across.

Everything else in the project I can take care of, but this part I'm just aware of how to even begin going about doing, nor would I even know what to call it if I wanted to do a google search on how to do it. I would be grateful for any pointers leading me in the right direction.

-Maximilian Libra, Gentleman Technosmith

Zeppelin Captain
Australia Australia

« Reply #1 on: May 16, 2010, 07:07:19 am »

If I was going to do this myself, I'd get a small meter from a cheap  'battery tester', like this one.

Open it up, extract the meter unit from that shabby unwanted plastic case, and replace the background image with a new one.

Assuming that you're starting with a functioning camera flash with an LED light already in it, then the next step would be to simply wire up the meter in place of the LED (50/50 chance of getting it around the right way first time).     It is entirely probable that the circuit that powers the LED has enough drive to run the meter at more than full deflection.     If, as one hopes, this is the case, then personally I'd just dive into my collection of spare resistors and by trial and error find one of suitable size to knock it back down to 100 percent deflection.    

Done this twice before, so its worth a try.  

And assuming that you dont have a big collection of resistors on hand, buy a few 'trimpots' of various size.
Total cost for this project will be under $10.
« Last Edit: May 16, 2010, 07:10:27 am by alfa1 » Logged
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