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Author Topic: DIY Pocket voltmeter  (Read 4748 times)
Professor J. Cogsworthy
Zeppelin Captain
United States United States

Aude Aliquid Dignum

« on: February 28, 2012, 04:11:06 pm »

From volume 1 of The Boy Mechanic

A Pocket Voltammeter [330]
Remove the works and stem from a discarded dollar watch, drill two 3/16 in. holes in
the edge, 3/4 in. apart, and insert two binding-posts, Fig. 1, insulating them from the
case with cardboard. Fold two strips of light cardboard, 1/2 in. wide, so as to form two
oblong boxes, 1/2 in. long and 3/16 in. thick, open on the edges. On one of these forms
wind evenly the wire taken from a bell magnet to the depth of 1/8 in. and on the other
wind some 20 gauge wire to the same depth. Fasten the wire with gummed label, to
keep it from unwinding.
Glue the coils to the back of the case and connect one wire from each binding-post as
shown in Fig. 2, while the other two wires are connected to an induction coil lead which
is inserted in the hole from which the stem was removed. Fasten a brass-headed tack to
the case at the point F with sealing wax or solder and bend a wire in the shape shown in
Fig. 3 to swing freely on the tack. Attach a piece of steel rod, 3/4 in. long, in the center
coil, C, Fig. 2.
A rubber band, D, connects the steel rod C with the top of the watch case. The ends of
the rubber are fastened with sealing wax. The rubber keeps the pointer at zero or in the
middle of the scale. Do not use too strong a rubber. A dial may be made by cutting a
piece of stiff white paper so it will fit under the crystal of the watch. An arc is cut in the
paper, as shown in Fig. 1, through which the indicator works.
To calibrate the instrument, first mark the binding-post A, which is connected to the
coil of heavy wire, for amperes and the other post, V, to the coil of small wire for volts.
Connect the lead and the post marked A to one, two and three cells and each time mark
the place of the pointer on the dial. Take corresponding readings on a standard ammeter
and mark the figures on the dial. The volt side of the dial may be calibrated in the same
manner, using a voltmeter instead of the ammeter. The place where the indicator comes
to rest after disconnecting the current is marked zero.


No, no no, a thousand times no. Its pronounced - lah-BOHR-ah-tor-ee
Professor J. Cogsworthy
Zeppelin Captain
United States United States

Aude Aliquid Dignum

« Reply #1 on: February 29, 2012, 01:02:13 pm »

Instead of a watch case I'm thinking about a round tin with a "window" lid....

Might even be able to electroprate them....

I need to do more research to see what voltages I would be able to build these for.
Mr Peter Harrow, Esq
Zeppelin Overlord
United Kingdom United Kingdom

Fellow of the Victorian Steampunk Society

« Reply #2 on: February 29, 2012, 01:07:34 pm »

no good for me I'm afraid, I don't have an electricity supply to my pockets

Proudly giving the entire Asylum The Finger!
Professor J. Cogsworthy
Zeppelin Captain
United States United States

Aude Aliquid Dignum

« Reply #3 on: February 29, 2012, 01:17:43 pm »

I'm thinking scratch built round voltmeters for 120v if I can figure out how to
make them handle more voltage..... and I wonder what they would do for AC
current as opposed to DC.
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