Make-it guide – a conductivity indicator for chemical solutions and
materials
Battery
Carbon fibre
rod electrodes
Resistor
Light emitting diode
Materials
 Instrument case, approx. 90x70x30mm with removable panel and compartment for 9 volt PP3
battery. www.rapidonline.com, order code 30-3803, www.rs-online.com RS stock no. 741-7470
 Battery, 9 volt PP3 and battery clip with connecting wires
 Sockets 4mm, panel mounting x2 (red and black)
 Light emitting diode (LED), 20mA and rubber holder
 Resistor, 390-500Ω, 0.25W
 Connecting wire, extra flexible, 55/0.1mm copper, PVC coated
 Banana plugs, 4mm x2 (red and black)
 Carbon fibre rod, approx. 1.5mm dia, www.Thehighwaymen.co.uk
 Electrical terminal block, 2 terminals wide
Procedure
Assembling the circuit inside the instrument case:
1. Drill two holes in the removable end panel of the instrument case. This is most easily done
with the case intact. The holes must be big enough to accommodate the sockets (approx.
8mm) and not too close together.
2. Unscrew and remove the case cover to allow access to the inside of the case. Insert a
socket into each hole and tighten the retaining nut.
3. Drill a 7.5mm hole in the top centre of the casing, near the end where the sockets are. This
is for the LED.
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4.
Push the LED through its rubber holder and insert into the 7.5 mm hole. Trim the negative
(shorter) wire of the LED to about half its length.
5. Trim the connecting wires on the battery clip to approx. 10cm and strip the ends.
6. Trim the wires of the resistor to about half their length. The inclusion of the resistor in the
circuit limits the current (I=V/R = 9/390 = 0.023A) flowing through the LED.
Work in a ventilated area when soldering
Use “rosin free” cored lead/tin solder
Wear safety glasses as the flux in solder can sometimes spit
7. Solder the red connecting wire from the battery clip to the terminal of
the red socket; solder the positive wire of the LED to the terminal of the
black socket. Details of this procedure are as follows:
o Insert the wire through the hole in the terminal of the socket and
bend back on its self.
o Heat the wire and terminal joint with the tip of the solder iron.
o Whilst still heating, touch the solder onto the surface of the joint.
The solder will melt and flow over the joint.
o Remove solder and iron.
8. Solder the black connecting wire from the battery clip to one of the
resistor wires; solder the negative wire of the LED to the other
resistor wire. Details of this procedure are as follows:
o Bend the end of each wire to be joined into a small loop.
o Interlock the loops and squeeze together.
o Heat the joint with the tip of the solder iron.
o Whilst still heating, touch the solder onto the surface of the
joint. The solder will melt and flow over the joint.
o Remove solder and iron.
9. Connect the battery onto the clip, place inside the instrument case and screw on lid.
Making the electrode holder and connecting wires:
1.
2.
3.
4.
5.
6.
Cut two lengths of connecting wire (approx. 30cm) and strip both ends.
Tin one end of each wire. Details of this procedure are as follows:
o Heat the end of the wire with the tip of the solder iron.
o Whilst still heating, touch the solder onto the wire. The solder will melt and flow along
the wire.
o Remove solder and iron.
Remove the plastic covers from the banana plugs and tin the metal “bucket” at the end of
each plug using the same technique as above.
Place the tinned end of one wire onto a tinned “bucket” and reheat to join them together.
Repeat for the second wire and second bucket.
Thread the plastic covers onto each wire and screw onto the plugs.
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©CLEAPSS®, The Gardiner Building, Brunel Science Park, Kingston Lane, Uxbridge UB8 3PQ
Tel: 01895 251496; Fax: 01895 814372; E-mail: science@cleapss.org.uk; Web site: www.cleapss.org.uk
7.
8.
9.
Insert the other ends of the wires into the terminal block and tighten the
retaining screws.
Using pliers cut two 40mm approx. lengths of carbon fibre rod for the
electrodes; alternatively use steel (open up a paperclip) or copper wire
for the electrodes.
Insert the electrodes into the terminal block and tighten the retaining
screws. To make the connections more robust glue around the wire and
electrode connections in the block (a hot glue gun works well).
To use the tester, make sure the battery is connected and simply dip the ends of the electrodes
into the solution or place on the material to be tested. The LED will light if the solution or
material conducts sufficient electricity.
GL 166 12/2014
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©CLEAPSS®, The Gardiner Building, Brunel Science Park, Kingston Lane, Uxbridge UB8 3PQ
Tel: 01895 251496; Fax: 01895 814372; E-mail: science@cleapss.org.uk; Web site: www.cleapss.org.uk