Wireless scoring equipment

[james bird]

Anyone had a chance to see/ play with any of this new cordless/ wireless scoring equipment yet?
I've a desire to make some scoring kit for my club, and am confident I can make a box that flashes and buzzes at the right times, for a fraction of the price of a commercial box, but I can't see an easy way to replicate the spools. Therefore radio is the answer, for £30-40/ $60-80 a player I think I can get a link working BUT and here is my issue - How does the weapon know the difference between on and off hits? With no direct return path between the lame an the tip, I puzzled as to how the system know.
Any ideas?

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James Bird
sa-fc.org.uk

[arcon]

[ 10-23-2001: Message edited by: arcon ]

[Oor Wullie]

Never seen it, but here's my hypothesis:

A transceiver is attached to the bottom of each fencer. When a hit is scored (by the traditional method of detaching the circuit from the earth), the scorer's transceiver sends a message to the box to say 'I've hit something'. As the tip, and thus the opponents lame will now be pulled to a high voltage, the transceiver connected to the lame can detect this signal line and send a signal to the box saying it has been hit. If the box doesn't receive this signal, then it knows the hit which has been announced by the scorer's transceiver is off target.

Make sense? Maybe, maybe not, but it seems reasonable to me...

[ledgerto]

Loved the homepage, James.
Great photos.

[aussie]

Hi all,

a system that has been used for a while is a box that can be made that fits the lame wires into a box and beeps when the epee hits something, a change on this theme may be able to fix the problem? and transfer the signal to uhf based on the connect circuit from the connection with a lame? to signal an off target a different frequency based on no conection of the circuit with a lame.??

im not sure if this will work but its only an idea?

[Tim McMackin]

Coach had an interesting idea the other day. It requires a new foil design, but it should make the electronic logic easier:

Suppose the tip of the foil had two semicircular conductors separated by a hair-thin insulating "equator." Fencers wear the same standard conductive lame, and are careful to not wear any other conductive material. When the tip is depressed into a lame, the two conductive hemispheres on the tip are connected by the wire on the lame, signaling a hit. Any time the tip is depressed on a non-conductive material, there is no complete sircuit between the two halves of the tip, signaling an off-target.

There are disadvantages, though, like it would be tough to ground a strip or the weapon guards. Just another thought.

Tim

[darius]

The problem with that is that any conductivity screws you up -- if I sweat a bunch through my glove, it's OK, because it's not in contact with my lame, so it'll register off-target.

With your coach's proposed design, that wouldn't happen.

darius

[Oor Wullie]

Interesting idea. This design could potentially make flicking impractical as well, as the full tip does not make contact during a flick, and the fencer could never be sure if the tip was rotated to the right orientation to short the two hemispheres.

[Mergs]

I've watched this discussion for a number of years (over on rec.sport.fencing) and the fundemental problem remains the grounding of the strip and weapons. Anyone heard of progress in that arena?

[BarryTice]

Tim --

The trouble with a split tip, as you mention, is that a hit on the opponent's bell would also show as on target. A complete system must rule this out as well.

My (imperfect) understanding of the current approach is that it is based on radio frequency interference.

Consider your weapon (foil, for example) as an antenna. The size of your antenna is essentially fixed, set by the combined length of your foil and body cord. There can be slight variations in the effective length based on body position, but it will fall within a certain range.

At a given length, an antenna is most effective at receiving signals of a certain wavelength. If you change the length of the antenna, it will become less effective at receiving signals of that wavelength and more effective at receiving a different wavelength. That's why old rooftop TV aerials had multiple lines of tines, to effectively receive multiple channels.

The length of your antenna changes when your foil scores a hit on your opponent's lamé. It also changes (approximately doubling) if you make a "hit" on your opponent's bell. Finally, it also changes when you make a touch on a metal strip.

There is always some "background" radio frequency noise around us these days, so there will always be some level of signal the weapon system can grab. In each of these states (touching nothing, touching weapon, touching lamé, touching strip), the character of the best-received incoming signal will change. (When you touch the strip, you will have a very long antenna, best suited for a long wavelength, e.g. a low-frequency signal.)

The tricky part here is having circuitry sensitive enough to distinguish between these four states. In Epeé, it's a little easier as you have only three states to discern. Also, the circuitry myst be flexible to allow various starting configurations, as someone with a youth-sized body cord and a No. 1 foil should still be able to use it.

Of course, all this signal interpretation should be done in the circuitry attached to the fencer, with that circuitry sending some message (hit/on target, hit/off target) to whatever receiver element is plugged into the scoring box. This way, the radio equipment replaces the reels (or bungees) and floor cords, but would not require a special radio-equipped scoring box.

Unless you're really up on RFI, the circuitry is probably beyond you. (I'm assuming that; I know precious little of RFI circuitry myself, but I can't imagine that this level of flexibility would be simple. Otherwise the products would already be cheap and plentiful.) And, if you hadn't already considered RFI as the solution, you're probably not really up on RFI circuitry.

Of course, there's nothing like a worthwhile project to provide an excuse to learn something new...

Hope this helps. -- b.r.t.

p.s. Disclaimer: I make no guarantee that this is how things are being developed. My speculation comes from a conversation with Walter Triplette about a year and a half ago about future possibilities. It does seem to be an elegant solution, covering all the requirements without needing any changes in current equipment (weapons, body cords, lamés), so I would imagine this is probably the path of least resistance for system designers.

[james bird]

Thanks for the replies guys. Barry, the closest I've got to a working hypothesis is as you suggest - the idea of using the weapon and body wire as a resonant circuit, and relying on a contact to the opponents lame as contact to a sufficiently large piece of metal that the 'tuned circuit' is damped, therefore allowing the 'blue cheese' to detect the difference between a hit and an 'on hit'.
Keep posting ideas, please - I'm determined to crack this one - Seems a low cost way of producing scoring equipment.
As for the discussion about 'split tip buttons' as mentioned, the issue is not just detecting the difference between and 'off' and 'on' hit, but relevantly an 'on' hit to only the opponents lame, conceivably a split tip could be used to register a hit to the players own lame.
All the best

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James Bird
sa-fc.org.uk

[Stryder]

Barry-
If I understand you correctly, you are suggesting that different frequencies be used to relay different signals to the scoring box. Right?
Wouldn't it be simpler to use one frequency for each fencer, with a small, independant scoring microprocessor in the sending unit (the unit carried by the fencer) Then a complex digital signal could be sent to the main scoring box.

Current radio technology suggests to me that the antenna size need not be significant. For a short range transmission any size antenna would do. Why would scoring equipment need more antenna than is used on a common FB radio or RC car? (~12 inches) If we could get a really complicated signal why do we need antennae at all? My Nokia doesn't have one.


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www.geocities.com/strydermike

[BarryTice]

Stryder --

I think you're misunderstanding me.

Each fencer would use only one frequency to send his or her signal to the receiver connected to the scoring box, as you suggest. The antenna for this transmitter (and for the receiver) would, in fact, be small (and quite conceivably hidden within the product packaging, as is the small antenna in your phone). The higher the signal frequency, the smaller the antenna needed to pick it up.

The different frequencies I mention (and the relatively large antennae) relate to the radio-frequency noise around us all the time, and the natural inclination of any piece of metal to act as an antenna to receive those signals. (Ever hear of someone's orthodontic braces or dental fillings picking up radio signals?)

When the size of the antenna changes (e.g., your foil touches something else metal), the wavelength of the signal it is best-suited to receive changes. Again, this is among the background radio noise, and does not have anything to do with the signal going to the receiver at the scoring box.

This change in the received signal from the foil-antenna is what indicates that a touch has been made on target. The challenge comes in distinguishing between the background noise signal from a foil touching no other conductor, a foil touching the opponent's bell (or the strip), and a foil touching the opponent's lamé.

Assuming the foil tip is pressed, the circuitry worn by the fencer would have to interpret the radio frequency interference signal and make a determination about the current size of the antenna, e.g., exactly what the foil is touching. The circuitry would then send one of two signals back to the receiver at the scoring box: Hit on target, or Hit off target. For that transmission, one frequency per fencer would certainly be sufficient. (For that matter, both fencers could potentially share the same frequency, depending on the frequency range used.)

Does this clear things up any?

-- b.r.t.

[oiuyt]

An additional issue....
If the tip is depressed, say from a hit to an arm, and the SIDE of the foil is in contact with either lame, wouldn't that look the same as the tip hitting the lame (at least in the sense of how large an antenna is generated)?

-B

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"Oh but you can't expect to wield supreme executive power just because some watery tart threw a sword at you!"

[Stryder]

Barry-

No. It does not. Are you saying that there would be a constant signal, like a tone emitted from the foil as part of your system, one that would vary when it increases it's size by touching the lame?

Or are you saying that there is just a lot of background noise that we can't help picking up and this would cause interference?

I thought the wireless systems would be self contained and encrypted signals from each sending unit. Without any creative ideas about how to interpret signals through the lame and strip and all that.

Can't these signals be processed independantly? Can't my sending unit tell when it has been hit by your weapon and send the signal back to the scoring box to turn on a red light?



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www.geocities.com/strydermike

[james bird]

Think what we have to do is make the center wire of the weapon the active element - When the button is opened (closed in Epee) the length of the element changes so it's resonance alters, so it can detect something has happened (a metal detector works like this, a resonant coil close to the ground that is detuned when it comes into close proximity to metal). So we've so far got 2 states 1. When the weapon is in it's 'rest' state, & 2. When the button is open (closed). Now we need a 3rd state - when the active element is touching the opponents lame. With an epee this seems fine i.e. At rest the active element is the center wire only. Off target the active part is the center and epee blade, on target it is the center wire, the blade and the lame. With foil there may be a problem in the 'blue cheese' detecting the difference between the rest state (center wire and blade) and an on hit (center wire and lame) - Therefore it'll have to have some form of conventional 'DC' circuit to detect this bit - thinking on the fly here.
Oiuyt asked if it could detect the difference between the blade edge touching the lame and the tip - wot a good question - guess we need to choose the resonant frequency carefully, so it is markedly larger in amplitude at the tip than along the blade length.
Stryder asked if the opponents jacket could signal it had been hit - probably - then we could use the 'sum' of the information from the attacker (hit or no hit) combined with the 'victims' information (on or off) - I'll put that in the 'things to think about' pile. This is all getting a bit hard! Me thinks I'll just have to get on and build one and see if it'll work before it makes my hair stand on end or starts to draw sparks from the opponents jacket.
I'm not to worried about the control box/ logic that makes the lamps buzz and the buzzer flash. I think that is just a bit of microprocessor magic, and a few chicken bones or lizard tales or what ever they use in such things now days. It's just this link between the fencers and the box that I'm trying to crack.
Please keep confusing me with ideas, it's all helping me to formulate an idea.
All the best

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James Bird
sa-fc.org.uk

[Mergs]

OK, time for the mechanical guy to step in. First off, if the center wire is used as the "antenna" element, how does one account for the variations in the wire length in the at rest condition? Secondly, how are length variations handled when the blade bends? Or are the length of the wire to frequency variations not that dependant? Or can S/W be done that checks the "resting" state of the weapon and set that as the zero state which then is used to make a comparison for when the point is depressed and the antenna length changed. Seems to me that the split/concentric two part tip may be the answer. As for epee a similar design can be used that can be used to detect when the tip is depressed against metal so that the circuit blocks the setting off of the light, similar to the timing circuit on the box.

Or am I coming across as not really knowing what the hell I'm talking about?

[neevel]

One thought I've had is to drive the relevant conductive surfaces-- the lame, the weapons, and piste-- with different periodic signals (pulse train, sine, whatever works best), and then have the unit examine what the period of signal it's seeing on the B-line of the foil is when the tip changes states. If you see the other side's lame signal, then it's a valid hit. If you see the piste signal or other-side's-weapon signal, no hit. If you see the lame signal and the weapon signal superposed, the opponent's weapon is in contact with the lame, and show a valid hit (anti-blocking-- has anyone been thinking of that ?). If nothing, off target.

-Dave

[edew]

Barry,

wouldn't hitting the bell guard have the same effect as it has now? That is, since the bell guard can be connected to "ground (via the body cord), the current will spill into that line as well, and it can be detected.

One way to make the device work for some amount of flicking is to make the two pieces concentric rings. You'll have an inner cylinder, then a thin annulus of insulation, then the outer annulus for the return circuit. Indeed, you only need one wire again, as the outer cylinder will ground to the blade. Thus, in this case, the circuit is always open (as opposed to the existing case where the circuit is always closed), and when the hit occurs on the lame, it will close it.

The problem is in detecting off-targets. In that case, perhaps a sensor to note tip is pushed down, but no current flow has occurred. Maybe it might require two wires.

[james bird]

Some of this is getting a bit 'off message'. There are now FIA approved wireless sets, which importantly must use existing weapons. I don't see much point (ha ha) in developing a system that needs fencers to use a non standard weapon.
Mergs - you ask about variations in wire length - Don't know, lets assume to start that apart from a standard weapon, the fencers use a standard body wire, there is obviously enormous difference in length and routing from one player to the next. If the 'exciter' circuit is driving the weapon via the body wire, as you imply there will be large variations to cater for. Perhaps as you suggest a 'dynamic' rebalancing will be required, may have to be continuous to cater for the different parameters between 'on guard' and arm extended.
Neevel - like your idea of the 'signal identifiers' but I think the problem is that as the 3 parts (fencer 1, fencer 2, piste and scoring box) are completely isolated units, there is no common ground, therefore fencer 1 equipment picking up a signal from fencer 2's lame will be difficult (lack of a common reference point, a bit like trying to swim in space - nothing to push against).
As for the flickers - let them suffer with the rest of us using conventional buttons. The less we do to encourage them the better - Its not a real hit - wouldn't have worked in 'steam foil' and wouldn't have done a lot of harm in a real dual - it's a weakness in the tie up between 1. the back being in target, and 2. electric scoring. (I'll get down from my hobby horse now, thanks for listening).
All the best

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James Bird
sa-fc.org.uk