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Converting LED output units

Gliderflyer

Nov 30, 2020
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Hello,
I just signed up here to try and find some help or to see if what I'm thinking of is even reasonably possible. I am an airgun shooter and many of us are using a cheapo Chinese Chronograph to test our guns. The unit has a 3 digit LED display and only outputs in meters/second. I would like it to output feet/second. Is there a reasonable way to read the the actual display and convert the units to the FPS reading I'm looking for? Perhaps on a second display? Our airguns sometimes exceed 1000 FPS so a fourth digit would be nice but if it was limited to 999 FPS that would be acceptable as well. My electronics knowledge isn't all that great but I do have help from my analog synthesizer building son.

FYI The unit we are using is here:
https://www.amazon.com/aikeec-Preci...&keywords=chronographs&qid=1606193935&sr=8-11

Thanks for any input.

Randy
 
Last edited:

KMoffett

Jan 21, 2009
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Probably not doable without major physical modifications...but: Reduce the distance between the LED emitter and detector pairs by a factor of 0.3048.
 

Harald Kapp

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upload_2020-11-30_19-54-30.png
May be a bit difficult on the sensor side if the sensors are mounted to a single PCB. But should be manageable.
 

bertus

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Nov 8, 2019
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Hello,

@Harald Kapp , Not only the emittor should be moved, also the receiver, wich is probably in the box should be moved.
This looks quite a challenge to me.

Bertus
 

Gliderflyer

Nov 30, 2020
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That's a great idea, I hadn't thought about working it from that end. These units are all said to have great consistency but sometimes accuracy is off somewhat. Not enough to matter for our purposes, usually within 2%. If I can find a way to make the sensors movable, perhaps using a small threaded rod and lock nuts, it would also allow calibration of the distance between.

Airguns are quite a hobby with lots of DIY gunsmithing to keep them tuned for best accuracy. Usually lower power is more accurate for the spring air powered guns I shoot. Along with working on the guns themselves, it's projects like this that keep the hobby interesting.

Thanks!
Randy
 

KMoffett

Jan 21, 2009
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Be interesting to see the inside of the box. I'm assuming that the power for the IR (?) LEDs in the base plate comes down the standoffs.
 

Gliderflyer

Nov 30, 2020
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Mine is still on its way to me, haven't received it yet. One thing is that the whole unit is 5.1" long. Given that, and just eyeballing from the picture, the emitter receiver setup is a pretty short distance. Let's call it 3.5" for the sake of argument. Reducing that to .3048 gets them down to just over an inch apart. It'll be interesting to see if it can get a good reading in such a short distance. Could be it's just easier to do the math conversion manually after getting the meters/second reading. That's what everyone else is doing but I'm hoping I can hack something here just for fun.
 

KMoffett

Jan 21, 2009
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Or tape a little calculator to the top of the box and put 3.048 in the memory. ;)
 

AnalogKid

Jun 10, 2015
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Or tape a little calculator to the top of the box and put 3.048 in the memory. ;)
That was my first thought - this sounds lik a 99-cent problem.

Or, just multiply by 3 in your head. The error is only 1.6%, and you will be surprised how quickly you will adapt to doing it quickly once you start doing it a lot. Every engineer who now bounces back a forth between metric and English units didn't always bounce ...

ak
 

AnalogKid

Jun 10, 2015
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With consistency better than accuracy, it sounds like they are relying on the LED beam focus to prevent the two receivers from seeing the wrong emitter. My guess is that there is no (or maybe only 1) calibration adjustment inside the box, and that moving the emitters close together will cause problems. A quick fix would be a piece of black-painted cardboard between the two emitters with a 0.5" dia. hole in the path, but I don't see the unit functioning well unless the receiver also is moved, and it probably is on a pc board.

ak
 
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