Fencing.Net - Your Guide to Fencing & Fencing Equipment

Sud · 07-10-2002, 06:50 PM

lochinvar,

1. generating AC signals from DC power is easy. For example, a 555 timer is an 8-pin chip that it designed to generate AC signals from DC power rails. Microcontrollers are more advanced than the 555 timer and will be able to do this very easily.

2. The switch in an epee's tip is electrically insulated from the rest of the weapon. That's why there's two wires running down an epee blade. The epee won't 'hear' its own AC signal.

3. Microcontrollers use about 10 micro-Amps in standby mode, and only a few milli-Amps when running. The battery would last a reasonable length of time - about the same time as a TV remote control, which also use batteries to generate an AC signal.

AC is the secret to not needing a common ground.
Fencer 1's epee will have an AC signal on their guard. What you do is put a capacitor in series with the epee tip. Capacitors block the passage of DC current but allow AC current to pass. So, the AC signal on the guard will pass through to fencer 2's buzz box. The microcontroller can detect the AC signal (with appropriate DC bias).

I'm saying it's possible. It is a more involved design than the simple 'if the tip is pressed, make a buzz' circuit, which is probably why the fencing equipment makers haven't bothered to make one yet. Plus, it won't handle lockout timing, so it is really only useful for training.

Mergs · 07-11-2002, 08:03 AM

I want to say thanks to you guys (and gals, so that I can stay PC) about starting and continuing this thread. I just got my box from PBT and started using it to practice my "flips" (not real flicks, but getting there!) and found out why they weren't going off during bouts! WOOHOO! I can REALLY be dangerous, now!

Good discussion, keep it up.

lochinvar · 07-11-2002, 11:19 AM

<blockquote>quote:<hr />Originally posted by Sud:
lochinvar,

1. generating AC signals from DC power is easy. For example, a 555 timer is an 8-pin chip that it designed to generate AC signals from DC power rails. Microcontrollers are more advanced than the 555 timer and will be able to do this very easily.

<hr /></blockquote>Doesn't a 555 timer really generate pulsating DC rather than AC? (It's been several years since I last dealt seriously with semiconductor devices, so bear with me here; my field is factory automation, so I live in the 480V three-phase world.) Are there DC devices that actually simulate AC by switching the polarity of the signal?
<blockquote>quote:<hr />
2. The switch in an epee's tip is electrically insulated from the rest of the weapon. That's why there's two wires running down an epee blade. The epee won't 'hear' its own AC signal.
<hr /></blockquote>So I gather what you're really describing is generating two signals, one straight DC for the tip and one pulsating DC (or AC, if you will) for the bell. That wasn't clear before.
<blockquote>quote:<hr />

3. Microcontrollers use about 10 micro-Amps in standby mode, and only a few milli-Amps when running. The battery would last a reasonable length of time - about the same time as a TV remote control, which also use batteries to generate an AC signal.
<hr /></blockquote>Point conceded. Not much power used. (If I'd thought about it some more, I'd have realized that cell phones and the like neither generate much heat nor consume much power. Duh.)
<blockquote>quote:<hr />

AC is the secret to not needing a common ground.
Fencer 1's epee will have an AC signal on their guard. What you do is put a capacitor in series with the epee tip. Capacitors block the passage of DC current but allow AC current to pass. So, the AC signal on the guard will pass through to fencer 2's buzz box. The microcontroller can detect the AC signal (with appropriate DC bias).
<hr /></blockquote>Okay, you've lost me again. Wouldn't putting a cap in series with the tip actually block your own signal? Don't you need the DC on your own tip to get through when the circuit is closed?

I guess what I can't get my head around is using one sensor (the tip) to detect and distinguish between the same event under two different sets of circumstances.

Scenario One: You hit your opponent in valid target, and the tip closes a circuit.

Scenario Two: You hit your opponent on the guard. Exactly the same thing happens at the tip as in Scenario One, it closes a circuit. The only difference is that the tip also now picks up whatever AC signal is being put on the opponent's guard in addition to it's own signal.

And how do you "source" signal from one power supply and "sink" it to a different power supply unless the two power supplies are somehow connected to provide a complete current path? (Even an AC circuit, which technically has no circuit "ground", still needs a complete current path.)

Seems to me that some sort of radio coupler or amplifier that would allow the box to modulate its own signal under certain circumstances would be needed... which granted wouldn't be too much of a problem, but would make the circuit more complicated...

If there's something I'm missing here, please feel free to point it out.
<blockquote>quote:<hr />

I'm saying it's possible. It is a more involved design than the simple 'if the tip is pressed, make a buzz' circuit, which is probably why the fencing equipment makers haven't bothered to make one yet. Plus, it won't handle lockout timing, so it is really only useful for training.<hr /></blockquote>I agree, I think it's possible. But I'm not sure all the theoretical questions about using AC have been answered. I'll have to give it more thought.

As for the lock-out feature, that might be the simplest problem to solve. A radio signal generated by Fencer A's box can activate a lock-out timer in Fencer B's box.

[ 07-11-2002, 02:25 PM: Message edited by: lochinvar ]

D'Artagnan1673 · 07-11-2002, 11:27 AM

Sud and Lochnivar,

I just wanted to let you two know that I am glad that someone understands how all of that works, because I am utterly lost just by the terminology

That isn't to say that I couldn't understand it after a bit of study.

lochinvar · 07-29-2002, 01:29 PM

Just an update:

I think I have found the answer to preventing touches from scoring on the guard in epee.

The solution requires re-designing the tip a little. Now if I can just find someone to machine a new tip for me without charging the national debt, I can test the sucker and let you all know how it turns out.

We could be on the verge of a $200 (or less!) complete scoring solution here with just two individual buzz-boxes: no reels, no wires, no main box...

D'Artagnan1673 · 08-13-2002, 08:39 AM

Loch,

Any additioanl news? Since I'm running the thought of starting a high school club in a year or two, the idea of a poor mans scoring system is highly appealing.

lochinvar · 08-13-2002, 12:41 PM

Nothing new to report. Still trying to find a machinist to make a prototype epee tip so I can test it--or, to be more precise, find one that will make it for less than the cost of a fully-decked-out SUV.

Also, I have to work up a circuit board with the radio circuits I have in mind for the lock-out. But that can be tested later.

I'll let you all know when I have something.

epeefencer74 · 08-13-2002, 06:43 PM

I have a few of those buzzers that plug directly into the epee and one from PBT that requires a body wire. I've used them exclusivly for training my students, although my students have borrowed them to use in bouts between themselves. These buzzers are not grounded, so hitting the opponent's guard would set them off. What my students have done is to have a couple of floor judges to decide if the guard or floor was hit as well as to help the director decide double hits. It's kinda like a hybrid between dry and electrical fencing.

botmer · 08-14-2002, 12:52 PM

I've bouted with those mini buzzers in epee and in foil. They are very practical. The epee ones were more stable, as they were attached directly to the sword by the 3 prongs, but the foil ones have just 2 prongs and the box is about the same size, so they went flying away sometimes when beating or parrying and fell crashing to the floor. So we had to put rubber bands around it to attach it to the foil's plug. One mini fell and stopped working but luckily they are easy to repair, in this case just a small cable got broken so we just had to solder it back. A disadvantage I see is that the light turns on but it's not so practical because one cannot see always it's own light and may confuse the buzz with the other one's mini. It happened a few times. Apart from that, they are quite useful. Do you know who sells them/ how much do they cost?

D'Artagnan1673 · 08-14-2002, 01:36 PM

By any chance do they have differnt sounds. I.E. Fencer A's buzzer sound is different than Fencer B's. It would make sense as it would increase the judges ability to distinguish who hit first in epee.

epeefencer74 · 08-14-2002, 06:02 PM

<blockquote>quote:<hr />Originally posted by D'Artagnan1673:
By any chance do they have differnt sounds. I.E. Fencer A's buzzer sound is different than Fencer B's. It would make sense as it would increase the judges ability to distinguish who hit first in epee.<hr /></blockquote>No the ones I have sound very like one another, unless it starts gettine low on battery power, then it starts sounding funny. I think when they made the buzzers, they had intended them for use in training. Bouting, I assume was an extension of use for these buzzers and I think the manufactures never really considered putting in diffrent sounding buzzers to aid directing.

JEC · 08-14-2002, 07:20 PM

D'art.
Although test boxes have the same sound, Favero has a test box with a 1.0 sec sound and another of 0.1 sec. You could easily distinguish whether is the long or short sound. However, in a double touch, the short sound may be missed.

[ 08-14-2002, 10:27 PM: Message edited by: JEC ]