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G8MNY > TECH 14.05.07 07:14l 73 Lines 2295 Bytes #999 (0) @ WW
BID : 14581_GB7CIP
Read: GUEST OE7FMI
Subj: LED Test Screwdriver
Path: DB0FHN<DB0NOE<DB0GAP<DB0FSG<DB0MRW<DK0WUE<DB0RES<ON0AR<GB7CIP
Sent: 070513/2326Z @:GB7CIP.#32.GBR.EU #:14581 [Caterham] $:14581_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Feb 07)
(8 Bit ASCII Graphics use code page 437 or 850)
NEON TYPE
Neon lamps used to be used as a mains testing screwdriver using a high voltage
resistor (spiral cut) in series with a neon in a clear screwdriver body.
Metal /~~~~~~~~~~~~~~~~~~~\________
Screw ³³Spring[N E O N][1M]=============- Screwdriver
Top \___________________/~~~~~~~~ Blade
There were dangers with this..
1/ It was unsafe in sunlight where the dim orange light could not be seen,
2/ If dropped the neon was often broken & you could not easily tell.
3/ The current needed for the neon (100uA> flowed through you.
4/ Voltage > 80V was needed to strike the neon so not so good for 110V.
But they were much liked in TV trade as a instant guide to Line O/P stage
working with the high AC field near the LOPT.
LED TYPE
The new LED versions at first sight the layout looks identical to the neon
type. But they have an internal battery & are very sensitive to electric fields
& can do touch continuity testing as well, so an instant battery test is
possible each time the tester is used.
Metal /~~~~~~~~~~~~~~~~~~~\________
Screw ³³Spring[BAT&LED][2M]===============- Screwdriver
Top \___________________/~~~~~~~~ Blade
But in the battery & LED capsule is this circuit..
Metal
ÚÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄ>Screw
³ _³_ Top
+³ LED\_/
two _³_ ÃÄÄÄ¿
small Ü ³ \³
watch ÄÄÄ ³ ÃÄÄ2M2ÄÄÄ>[2M]-Blade
cells Ü \³ e/³
³ ÃÄÙ
³ e/³
ÀÄÄÄÄÄÄÄÙ
It works by operating a high gain darlington with current fed through the
external high voltage safety R through its own 2M2. It only needs 1 volt
positive (compared to -ve) to turn on the darlington.
The test circuit load is next to nothing & it can easily see the spiral voltage
field on the outside of double insulated internally twisted mains flex.
Problems with it are:-
1/ There is no limit on the LED current so it easily flattens the battery if
operated too long.
2/ It can't detect negative voltage, so can be dangerous on -ve DC circuits!
Why don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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