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Experiment 14: Silicon Amplification


16 March 2010 by Quest 2, to link in with Chapter 14 of our book.


To use a silicon transistor to make a touch switch to switch LEDs powered by a silicon solar panel.


The voltage and current our solar panel was capable of producing posed no risk of electrocution.


  1. Test LED arrays with multimeter (on diode test setting) to confirm polarity.
  2. Using clip leads, connect the solar panel to one of the LED arrays to ensure the solar panel and the LED array work.
  3. Connect an ammeter (on a multimeter) in series with the LED array to get a continuous reading of the current in the circuit, then position the solar panel for optimum current.
  4. Remove the silicon power transistor from its circuit board. Use more clip leads to connect the transistor in the circuit so that touching two probes with a finger will make the LED array turn on.
  5. With the solar panel in a suitable position (we had it on a chair – OK but not in the optimum position), have each person individually complete the circuit by touching the two probes with their two hands. See who can produce the greatest current to flow.
  6. Test with more people holding hands in a loop, with the end two people touching the probes.
  7. Connect two LED arrays in series and retest.

Materials & Equipment

  • 12 V solar panel (open circuit voltage 18+ volts).
  • LED arrays - one 12x 5mm LED 6 V array and one 9x 5mm LED direct drive.
  • Clip leads.
  • Multimeter.
  • Silicon power transistor.
  • Soldering iron, solder, soldering stand, water (for the cleaning sponge).


  1. The LED array lit up faintly when the multimeter leads were connected one way but not the other. This made it clear which way around we needed to connect the solar panel.

  2. The solar panel provided the greatest current when held at the window pointed straight at the brightest portion of the sky. Conditions were heavy overcast so the sun itself wasn't visible.

  3. Maximum current was about 25 mA. The LEDs in the array didn't light up evenly.

  4. When the transistor was first connected in the circuit the LED array turned on constantly. The base and emitter pins were probably mixed up, so the leads on those pins were swapped. The transistor switching then worked fine. Making and breaking the connection (ie, flashing the LEDs) verified that it was definitely the person switching the LEDs on. When the probes were contacted directly to each other the LEDs briefly flashed but otherwise were off.

  5. Initially the boys all produced a noticeably brighter light from the LEDs than Mr Mander (Ian) did. However, with a bit more effort Mr Mander and John got first equal at 10.7 mA. (That was the total current from the solar panel, not the amount flowing through the person.)

  6. Even six people in a loop conducted enough current to switch the LEDs on. With a finger on each cheek Mrs Steward had a beautiful smile.

    Item Touched With Finger or Hand Conductive
  7. The switching still worked fine and the two LED arrays drew about the same amount of current from the solar panel as a single array did.


  • A diode tester on a multimeter is useful.
  • Solar panels work best in strong direct sunlight.
  • Silicon transistors can be used to amplify a very small electric current and thereby provide a switching action.
  • Boys can be very creative in how they connect to each other to complete an electrical loop.
  • The tongue was probably not a good idea with the solder involved.
  • A solar panel can output a limited amount of current. By having two LED arrays connected in series, the solar panel produced twice the power, and therefore twice the light.
  • James officially likes playing with clip leads.