Experiments for better teaching

Low Cost Conductivity Tester

P

• battery holder for AAA cells with wires for PCP (printed circuit board) mounting
• 2*1,5V AAA cells
• ca. 25 cm 1,5 mm² copper wire from electric cable
• needle nose pliers
• overhead marker black

• universal PCP with copper stripes approx. 6*3,5 cm
• soldering rod
• green LED (5G - 7100 mcd)
• jumper wire (non isolated) approx. 0,6*3 cm
• diagonal cutting pliers

• soldering tin

1. Put on the soldering rod (350°C).

2. Mark one narrow side of the PCP with a black line (overhead marker) on the component side. Always make sure this line is on top(it marks hole row nr. 1 horizontally).

3. Solder two jumpers  on the component side: nr. 1 between  column nr. 10 (copper stripes) and 12, nr. 2 between column nr. 5 and 11. Thisfor cut a piece of jumper wire to fit (approx. 1.5 cm). Turn wire ends on solder side a little bit so it will not fall out of the holes. Solder it now.

4. Press battery holders in the holes (specified in component placement plan below) in row 4 and 5 resp. 10 and 11. Please note the polarity! Solder!

5. Now solder the LED:  short pin (kathode) to column 2, long pin (anode) to column 4.

6. Finally solder the test electrodes: trim the two 1.5 mm² wires to approx. 10cm and coat them with some solder approx. 1cm from one end. Same on the PCP on column 2 and 12 far ends (note: on the solder side!). Then put the wire end with solder on top of this column ends, heat it with soldering rod until  the solder melts. Ready.

Short circuit between columns: in case the LED does not light up or the batteries warm up this is due to a short circuit on your PCP. Check every solder pad and its vecinity.