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G8MNY  > TECH     17.10.18 08:15l 77 Lines 3145 Bytes #7 (0) @ WW
BID : 42126_GB7CIP
Subj: Volt Indicator Screwdriver
Path: ED1ZAC<ED1ZAC<IZ3LSV<IR2UBX<F1OYP<ON0AR<GB7CIP
Sent: 181017/0604Z @:GB7CIP.#32.GBR.EURO #:42126 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                    (Updated Aug 2007)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

This is the circuit of a 1 screwdriver voltage tester...

ROLSTON's ORIGINAL VOLTMETER SCREWDRIVER
If you have not seen one of these, they have a small LCD panel in the flattened
black handle.
  _________________________________
 /                                 ~~~---...___
  --     --       Ŀ   __           ~~~---...
 |()|< |()|<                (  )                  Ŀ
  --     --          ~~           ___...--~~~~~~
 \                                 ___...---~~~
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  

CIRCUIT
              ______________________________________
             com            L  C  D                
                   220V  110V  55V   36V   12V   ~ 
 DIRECT      -------------------------------<- Conductive Mats
  TEST                                      
   22M22MM92M911M22M710M)=======>SCREWDRIVER
                                                      NEON
   2M7
 INDUCTIVE
 BREAK TEST

DIRECT TEST
When you touch this button (earth) & prod the testing voltage, it indicates if
the voltage is greater than the displayed graphics. This occurs when any of the
LCD sections sees greater than about 1V. As the LCD current required for any of
the display sections is only the odd pA very high value resistors can be used
to make up the multiplier chain. This means the return circuit can safely be
made though ones finger to earth.

INDUCTIVE BREAK TEST
A neon is also fitted for a Inductive Break-point Test. (what ever that is? To
do with Fluorecent lamps?) It lights when voltages are above 80V, above 2V you
just see the ~ symbol on the LCD.

N.B. with this circuit, this test is not too safe, as current COULD flow
through the LCD to you! So I don't recommended you use the neon option as a
mains tester!


G8MNY's MODIFIED VERSION
To open the unit to improve the calibration & safety etc, pop out the back
panel cover & ...

1/ Change one of the 22M to a 10M (100V) to increase the sensitivity on DC.
2/ Then add a 270pF (20v) cap to reduce the sensitivity on AC.
3/ Add a 220k (250V) into the inductive break test circuit.

              ______________________________________
             com             L  C  D               
                   220V  110V  55V   36V   12V   ~ 
DIRECT       -------------------------------<- Conductive Mat
 TEST                                       
  22M10MM92M911M22M710M)=======>SCREWDRIVER
              Ĵ       NEON
                          270pF                        
  220k2M7
INDUCTIVE
BREAK TEST

Now test, & you should find the accuracy better & from DC-50Hz. And there is
no danger of electrocution if the neon indicator is used on Mains.


Why Don't U send an interesting bul?

73 De John G8MNY @ GB7CIP


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