plastic film canister
LED and resistor
soldering iron and solder
stiff copper posts
9 V battery cap
9 V battery
Step 1: Preparing the Canister
You need to make three small holes in the base of the canister through which you will stick the two probes (lengths of copper) and the glove of the LED. I used a small drill, you could also carefully poke through an ice pick or other small tool. Be careful not to make your holes too large, the fit needs to be snug.
I used a permanent marker to label the canister "conductivity meter" as well.
Step 2: Assembling and Testing the Circuitry
Connect these components together in a line (not a closed loop):
one copper probe
one end of the 9 V battery connector
then to the other end of the 9 V battery connector you solder on the second copper probe.
Before continuing, put a 9 V battery onto the connector and touch the two copper probes together to test the circuit. If the meter is working properly then the LED should remain lite while the copper probes are in contact.
Step 3: Assembling the Meter
Let the wires to the 9 V battery cap come out of the canister at the top and use the cap to hold them in place. Add your battery and you are ready to start testing materials!