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High gain amp circuit requ'd

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Dr_Doggy

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with my new coilgun , i have set up an optical Chrony to measure my velocities, however while using 3/4 pvc i have found my machine screws to be small enough to pass with out detection, i have treid using pots on my LEDs to turn down sensitivity, which has more success but not enough to satisify,

so i was thinking instead of redesigning, to use an inductive loop to detect when the machine screw passed through each point, however during my tests i notice that, magnets work very well to produce voltage in a single turn coil, but not enough for my tiny needle nose pliers which i believe to have a small amount of magnetism, however by significantly increasing the turns in the coil i was able to get a good response from my pliers.
however even with the scope down to 10mv i was still not able to see response from machine screw even with the larger coil,
based on my results i feel that i should be able to detect machine screw with large coil if i use high enough gain amp, and filters.
but i wonder mostly what amp should i use for this, my guess is that i should receive response at around 10uV +- 1000%, my output will feed to microcontroller digital port. just guessing...
 
have you tried a commercial firearm testing chrony? if they work ok with something as small as a .22 or a .177 pellet gun, they should work with your machine screws. i would think if you are using coils to pick up the machine screws, that the coilgun itself may interfere with your pickups, since they are likely close together, and on the same axis
 
there's plenty of optical ballistic chronographs on the market, some of them rather inexpensive...

or, here's another method make two screens out of wax paper which is under tension. a piezo sensor on each paper screen gives a spike with projo impact. not exactly a contactless method, so a very small error may result, but if the screens are under enough tension, the paper will separate and tear as soon as impact takes place, minimizing contact between the projo and screen, and introducing only very small losses in velocity.
 
Usually it's done by breaking wires or conductive foil.


to cheap to go shopping for this one, but what about a foil capacitor around the inner diameter of pvc, so when the screw travels through it causes a flux in capacitance? maybe 2 parallel foils on inside to make my cap? just in case i do coincidentally align pvc and screw happens to stay centered.
 
yr rite, it didnt work, ammo is just so small, i was playing around when i asked that; and i noted that two parallel strips of foil on the same side of a piece of cardboard showed a small capacitance, also for obvious reason when i put my hand, or some foil on the bottom side of the cardboard the capacitance significantly increased, however again ammo was just to small.

On another note though it was hard to get the photo detectors to give me a digital reading, but they work very well on the a/d inputs, so here it all is for <10$ (LCD is eject-able)
thnx again!

https://www.electro-tech-online.com/members/dr_doggy-albums-chrony.html
 
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