hit recorders

[Aerevon]

I was wondering...what exactly are those little hit recorders, and how do they work? See, I'm the daughter of an electrical engineer, so I always try and take stuff apart and figure out how it works, or try and build stuff instead of buying it. I was looking at those hit recorders, because it occured to me that one could really easily be made. I tried making a circuit with a little light it, and I found that when I hooked it to the socket on my foil, the light lit, and turned off when I pressed the tip. This sorta stumped me for awhile, because I know that's how the foil tip works, I just can't figure out how they change the wiring so that the light lights up when when you press the tip. I couldn't find any info on those hit recorders; what i was wondering, is do they count on and off target hits? because a little battery powered light that doesn't leave the fencers body has no way of knowing whether it's hitting lame or jacket.

by the way, yes, I know I am insane and I am proud of it

just seeing if there are any among you that are as crazy as I am....

[esskreemr]

Your foil has two circuits. When you hook your body cord in, it is connecting one circuit that is closed (ie electric is flowing). That circuit (call it circuit A) runs from the insulated plug, up through the blade wire, through a connector in the tip. The tip is spring loaded so that when it is not depressed, a sleeve keeps the circuit closed by connecting the tip to the barrel and back "down" the blade through the ground plug (non insulated plug) and back "out" the body cord to the reel. Basically, your foil is one giant circuit while the tip is not depressed.

When the tip is depressed, the A circuit is open (no electric flowing) because the tip loses contact with the barrel shutting the electric current off. If the tip is placed on a metallic vest when the tip is depressed, circuit B is connected and is now in a closed state electric passes through your blade, to the lame, "out" your opponents body cord and signals a hit. This circuit is grounded by the alligator clip on the body cord that is connected to the lame. This causes your colored light to go off.

If your tip is depressed against something other than the lame that is connected to your scoring circuit (circuit B), then the A circuit is open (no electric) and this causes your white light to be activated.

Sorry, I'm not an electrical engineer. This is of course a simplistic explanation and does not include timing.

Leon Paul has an excellent animated graphic with some information:
http://www.leonpaul.com/armoury/foil/foil_parts.htm

There will be some armorers along shortly to give you a better idea.

[DHCJr]

The answer above is good. Let me try to shorten it. The Foil circuit is normally closed. Ask your father about normally closed switches. They are available and used by anyone to test boxes.

When you hook up to one of the 2-light test box the light will come on. When you Unhook from a machine the white light will come on because it has a normally closed switch.

[DangerMouse]

I think what you're looking for is an inverter. If you send v+ to an inverter, it doesn't put out any power. If you cut off v+, the inverter sends v+.

[Aerevon]

I did some reasearch, talked to my dad, and looked up some schematics, and i've basically came up with a plan for how this thing is gonna work: you'll have a box strapped to your arm, that has an LED on it. This plugs into your foil and lights up when you get a hit, also beeping. It's pretty much impossible to see on or off target hits without being attatched to your opponent though, so it's gonna just be for "practice" bouting. I'm going to start building it, and as soon as I have it done I'll post some pics. It's a good deal if it works, only cost me 10 bucks for the parts (capacitors, resistors, ICs, breadboards)

[beeyeelelwhy]

I made a simple one for when i fenced epee. Cost probably less than 3 or 4 dollars to make one. It just lit up when the point was depressed. It was neat though because i taped a small magnet on the led light and stuck it in my mask so i could see it when it lit up and so could my oponent.