Elenco Electronics K-20 User guide

NERVE TESTER KIT
MODEL K-20
Assembly and Instruction Manual
Elenco Electronics, Inc.
Copyright © 1989 Elenco Electronics, Inc. Revised 2002 REV-E 753220

PARTS LIST
If you are a student, and any parts are missing or damaged, please see instructor or bookstore.
If you purchased this nerve tester kit from a distributor, catalog, etc., please contact Elenco Electronics
(address/phone/e-mail is at the back of this manual) for additional assistance, if needed.
Parts Verification
Before beginning the assembly process, familiarize yourself with the components and this instruction book.
Verify that all of the parts are present. This is best done by checking off each item in the box provided next to
the part in the parts list.
RESISTORS
Qty. Symbol Description Color Code Part #
1 R1 470W5% 1/4W yellow-violet-brown-gold 134700
1 R2 47kW5% 1/4W yellow-violet-orange-gold 154700
SEMICONDUCTORS
Qty. Symbol Description Part #
1 SCR1 SCR C106B 319106
1 D1 Diode LED red 350002
MISCELLANEOUS
Qty. Symbol Description Part #
1 T1 Transformer 442100
1 P1 Double Sided PC Board 510320
1 PC Board 518020
1 S1 Switch Push Button 540100
1 S2 Switch Slide 541102
1 Solder Roll 24” 551124
1 B1 Battery Snap 590098
2 Wire 9” 814920
1 H1 Wire 9” Bare 845000
-1-
Resistor Transistor
PARTS IDENTIFICATION
Battery Snap
LEDSwitches
SCR
Slide
Push Button
Transformer
IDENTIFYING RESISTOR VALUES
Use the following information as a guide in
properly identifying the value of resistors.
BANDS
12 Multiplier Tolerance
PC Board
Double Sided
PC Board
OR

-2-
INTRODUCTION
Test your nerve with the Nerve Tester Kit. It takes a steady hand, should you touch the twisted wire with the
probe, a slight electrical shock will be felt. The shock is very weak and harmless. For the weak of heart or
“chickens” a switch removes the electrical shock and substitutes a Light Emitting Diode (LED) which lights up
when the probe touches the wire.
THEORY OF OPERATION
The circuit of the Nerve Tester is shown on page 6 of this manual. The circuit consists of two basic circuits. One
is the high voltage generator and the other the LED with its latch circuit. We shall study each circuit further.
THE LED CIRCUIT
Figure 1 shows the basic LED circuit. Note that the battery is placed in a
series circuit with resistor R1, the LED and the Silicon Controlled Rectifier
(SCR). The positive voltage of the battery is placed on the anode of the SCR.
The negative voltage is connected to the cathode. Under these conditions if
a positive voltage is placed on the gate of the SCR, even for a 1/1000 of a
second, the SCR will conduct current and keep conducting when the positive
voltage is removed from the gate. This will keep the LED lit until the voltage
is removed from the SCR. This is done by closing switch 1, which shorts out
the SCR. Resistors R1 and R2 are needed to limit the current in the LED and
SCR.
THE SHOCKER GENERATOR
Figure 2 shows the basic circuit used to produce the high voltage of the
shocker generator. The heart of this circuit is the transformer. We shall review
the operation of a transformer to understand the circuit.
A transformer has two or more windings around an iron core. If a changing
current is placed in one of the windings, it will appear in the other winding.
The voltage across the second winding will be the ratio of the turns of the
transformer. If the first winding has 100 turns and the second has 1,000 turns
(10:1 ratio) the secondary voltage will be 10 times the primary voltage. In our
transformer, the ratio is 30:1. Therefore, the 9V battery voltage will be
stepped up to 270V on the secondary.
The primary wire of the transformer is connected to the negative side of the battery. The positive side of the
battery is connected to the twisted wire. The other primary wire is connected to the probe. When the probe
touches the twisted wire, a DC current flows through the primary of the transformer. The secondary of the
transformer will only have voltage the instant the probe touches the twisted wire and the instant the probe leaves
the wire. Again, only when the current changes. Refer to Figure 3 and note that there are two voltage spikes
for each time the probe touches the twisted wire. This is because the current changes twice.
Note that the probe is double-sided copper with an insulation in between. One side is negative (ground), the
other side connects to the high voltage. Your hand touches both plates and therefore you feel the shock.
LED
R1
S1
Cathode
Gate
Anode
SCR
Wire
Probe
R2
Figure 1
T1 S2 Wire
Probe
Figure 2
Figure 3
Current in
Primary
Voltage in
Secondary
+270
–270
Max
Zero

-3-
Introduction
The most important factor in assembling your K-20 Nerve Tester Kit is good soldering techniques. Using the
proper soldering iron is of prime importance. A small pencil type soldering iron of 25 - 40 watts is
recommended. The tip of the iron must be kept clean at all times and well tinned.
Safety Procedures
• Wear eye protection when soldering.
•
Locate soldering iron in an area where you do not have to go around it or reach over it.
•Do not hold solder in your mouth. Solder contains lead and is a toxic substance. Wash your hands
thoroughly after handling solder.
• Be sure that there is adequate ventilation present.
Assemble Components
In all of the following assembly steps, the components must be installed on the top side of the PC board unless
otherwise indicated. The top legend shows where each component goes. The leads pass through the
corresponding holes in the board and are soldered on the foil side.
Use only rosin core solder of 63/37 alloy.
DO NOT USE ACID CORE SOLDER!
CONSTRUCTION
Solder Soldering Iron
Foil
Solder
Soldering Iron
Foil
Component Lead
Soldering Iron
Circuit Board
Foil
Rosin
Soldering iron positioned
incorrectly.
Solder
Gap
Component Lead
Solder
Soldering Iron
Drag
Foil
1. Solder all components from
the copper foil side only.
Push the soldering iron tip
against both the lead and
the circuit board foil.
2. Apply a small amount of
solder to the iron tip. This
allows the heat to leave the
iron and onto the foil.
Immediately apply solder to
the opposite side of the
connection, away from the
iron. Allow the heated
component and the circuit
foil to melt the solder.
1. Insufficient heat - the
solder will not flow onto the
lead as shown.
3. Allow the solder to flow
around the connection.
Then, remove the solder
and the iron and let the
connection cool. The
solder should have flowed
smoothly and not lump
around the wire lead.
4. Here is what a good solder
connection looks like.
2. Insufficient solder - let the
solder flow over the
connection until it is
covered. Use just enough
solder to cover the
connection.
3. Excessive solder - could
make connections that you
did not intend to between
adjacent foil areas or
terminals.
4. Solder bridges - occur
when solder runs between
circuit paths and creates a
short circuit. This is usually
caused by using too much
solder. To correct this,
simply drag your soldering
iron across the solder
bridge as shown.
What Good Soldering Looks Like
A good solder connection should be bright, shiny,
smooth, and uniformly flowed over all surfaces.
Types of Poor Soldering Connections

-4-
ASSEMBLE COMPONENTS TO THE PC BOARD
P1 - Probe (see Figure A)
H1 - Twisted Wire (see Figure B)
B1 - Battery Snap
(see Figure C)
D1 - LED Red (see Figure D)
S2 - SPDT Slide Switch
T1 - Transformer
Insert the transformer into the PC board
as shown. Solder the four leads into place
and cut off the excess leads.
R2 - 47kW5% 1/4W Resistor
(yellow-violet-orange-gold)
R1 - 470W5% 1/4W Resistor
(yellow-violet-brown-gold)
SCR1 - C106B SCR
(see Figure E)
S1 - Push Button Switch
Figure A
Assemble the probe (P1). Solder an excess
lead from the resistors to a side of the double
sided PC board. Leave 1/2 inch extending from
the end. Form a loop at the end of the wire.
Cut two 9 inch wires and strip 1/2 inch of
insulation off of both ends. Solder a wire to
each side of the double sided PC board. Insert
the other ends of the wires in the holes marked
P1. Solder and cut off the excess leads.
Figure B
Bend the 9” bare wire into the shape as shown
below. Insert one end of the wire into the PC
board, in the hole marked H1 and solder into
place.
Figure C
Insert the battery snap wire through the PC
board as shown. Then, insert the red wire
into the positive (+) hole and the black wire
into the negative (–) hole. Solder and cut off
the excess leads.
Figure D
Mount the LED with the flat side of its body
in the direction as marked on the top
legend. Leave 1/4” between the LED and
the surface of the PC board. Solder and cut
off the excess leads.
Figure E
Mount the silicon controlled rectifier (SCR)
with the back side (metal backing) in the
same direction as the marking on the PC
board as shown.
B1
Flat Side
1/4”
Back Side
PC Board
Marking
PC Board
Marking
B
A

COMPONENT CHECK
1. Be sure that all components have been mounted in their correct places.
2. Has the LED D1 been installed correctly? The flat side of its body should be in the hole as shown on the top
legend. If the LED is in backwards, it will not light.
3. Pay close attention to the red and black wires of the battery snap. The red wire should be installed in the
positive (+) hole and the black wire in the negative (–) hole. Snap in a fresh 9-volt battery.
OPERATING THE K-20
1. Grasp the probe so that you touch the copper on both sides of the probe.
2. Try to guide the loop along the wire. If the
loop touches the wire, you will receive a
mild shock or throw the slide switch S2
and the LED will light instead.
3. Push switch S1 to reset the LED.
TROUBLESHOOTING
Contact Elenco Electronics if you have any problems. DO NOT contact your place of purchase as they will not
be able to help you.
1. One of the most frequently occurring problems is poor solder connections. Tug slightly on all parts to make
sure that they are indeed soldered.
2. All solder connections should be shiny. Resolder any that are not.
3. Solder should flow into a smooth puddle rather than a round ball. Resolder any connection that has formed
into a ball.
4. Have any solder bridges formed? A solder bridge may occur if you accidentally touch an adjacent foil by
using too much solder or by dragging the soldering iron across adjacent foils. Break the bridge with your
soldering iron.
LED CIRCUIT REMEDY
1. LED - Move switch S2 into position A (shown on the top legend drawing in the assembly manual). Place a clip-
lead from the cathode lead of the LED (the lead on the flat side) to the negative terminal of the 9-volt battery.
The LED should light. If the LED does not light, the problem is with the LED or resistor R1. If the LED is
installed with the flat side in the correct direction and R1 is the correct value, then most likely the LED is at fault.
2. SCR - Move switch S2 into position A. Place a clip-lead from the gate (G) of the SCR to the positive
terminal of the battery. The LED should light even when the clip-lead is removed. If not, the problem
could be with S1, be sure that S1 is in the open position first. If you get no response, place a clip-
lead from the center lug to the position A lug of switch S2. If the circuit works now, the problem was
S2. If the circuit still does not work, the problem is the SCR.
SHOCKER GENERATOR REMEDY
1. TRANSFORMER - Be sure that the transformer is installed correctly, with the three lead side in the direction
as shown in the top legend drawing in this manual.
2.
S2 - Place a clip-lead from the center lug to position B. If the shocker circuit now works, the problem is with S2.
-5-
CAG

-6-
SCHEMATIC DIAGRAM
QUIZ
1. The nerve tester produces a ______________ whenever the probe touches the twisted wire.
2. A “chicken” afraid of the shock will switch the nerve tester to the ______________ position.
3. The LED will light when a positive voltage touches the ___________ of the SCR.
4. Once the LED is lit, removing the probe from the twisted wire will turn off the LED. (true or false)
5. A transformer has ___________ or more windings.
6. A _______________ current in the primary winding will produce voltage in the ___________ winding.
7. The voltage in the secondary winding is equal to the primary voltage times the ratio of the ____________ in
the transformer.
8. The nerve tester produces about a ____________ volt spike for a very short time.
9. There are ___________ spikes of voltage every time the probe touches the twisted wire.
10. The probe has ___________ sides of copper between an insulator.
Answers: 1. shock; 2. LED; 3. gate; 4. false; 5. two; 6. DC, secondary; 7. turns; 8. 270; 9. two; 10. two
B1
R1
470W
R2
47kW
T1
S2 S1
A
B
D1
LED
C106B
SCR1
H1
P1
Probe

Elenco Electronics, Inc.
150 W. Carpenter Avenue
Wheeling, IL 60090
[phone]
http://www.elenco.com
e-mail: [e-mail]