Epee touch-sensor device

[Matt Mason]

Recently I saw a device advertised that plugs into the electrical
aperture on an epee, and indicates the closure of a circuit when the
tip is depressed by lighting a small LED light and beeping/buzzing. I
would think that this would be a fairly simple device to make rather
than purchasing it, but I'm not too handy with circuit design. Has
anyone ever seen a schematic for a device like this, or built one
yourself, who might be able to provide the specs?

Or, barring that, anyone have a used one to sell (or an exceedingly
good price on a new one)?

Thanks, - Matt

[Andrew John]

Matt,

A cheap digital multimeter in "continuity" mode does this.
Re-terminating the leads with bits from an old body wire if
you want to get fancy.

If you want to build something, then all you need is this:


+--- Eppe --+------------+
| | |
| Resistor Buzzer
Battery | |
| LED |
| | |
+------------+-------------

So you are right about it being cheap to make.
With a 9V battery, the resistor is needed to limit the current to
the LED. Depending on how fancy the LED is it will be rated for between
20mA - 50mA, and want to see no more than 2V, so the resistor would need
to be about 350Ohns, and rated for at least 1/4 Watt.

( 9V - 2V ) / 0.02A = 350 Ohms
( 9V - 2V ) * 0.02A = 0.14 Watt

Smaller resistor = LED brighter, and die quicker.
No resistor = puff of smoke

If you want to get fancier, and have a little box you can actually use for bouting,
( or better yet 2 ), then you need to add a delay off timer ( 555 chip is fine ),
as otherwise you will never hear the buzzer when hitting, 'cause the epee tip is only
"on" for a few msec in a normal hit.

I've built such boxes for foil, but gave up on trying to get off targets to work -
requires either a nice big capacitor if you don't mind electrocuting the odd foilist, or some
sort of RF signal superimposed on the lame, and a contact radio receiver connected to the tip
if you are feeling kinder, as I was. Given only a few msec to detect the signal duing lame contact,
it was never reliable. The timing of hits is also pretty hard to tell from the sound alone - with epee's
double hit being impossible to determine, unless you make the boxes talk to each other, and
preferably some lights ( add more $ ).

In order of difficulty the basic problems for electronics in fencing are:
1) Speed - hits are very quick
2) Communications - especially in epee
3) Sweat
4) Cheating ( encryption is easy these days, interference is more of a problem ).

You may find the following discussion informative:

http://www.fencing101.com/vb/showthr...&threadid=6658

Regards
AJ

"Matt Mason" <mjmason@juno.com> wrote in message news:ca08463e.0307111453.471de1c@posting.google.co m...
> Recently I saw a device advertised that plugs into the electrical
> aperture on an epee, and indicates the closure of a circuit when the
> tip is depressed by lighting a small LED light and beeping/buzzing. I
> would think that this would be a fairly simple device to make rather
> than purchasing it, but I'm not too handy with circuit design. Has
> anyone ever seen a schematic for a device like this, or built one
> yourself, who might be able to provide the specs?
>
> Or, barring that, anyone have a used one to sell (or an exceedingly
> good price on a new one)?
>
> Thanks, - Matt