The Nightlight

In this lab, we were given an LED nightlight circuit. Upon first glance we noticed all the components, the zener diode, 3 resistors, a capacitor, 4 diodes, a photocell, an LED light, and something we thought was a transistor. We knew the first thing to do was to identify all of the components and find out the rating for them. We had to use the microscope to determine the identifying numbers on the zener diode, the capacitor, and the, assumed, transistor. The zener diode read 1N5242B, the capacitor read 334J, and the transistor read 9014C. After searching online we discovered that a 1N5242B zener diode is rated for 20 mA, the capacitor value was .33uF, and the transistor was, in fact, a transistor. The resistor values were determined by simply reading the color code. This was a little tricky on the blue one, but we found the values to be 1Mohm, 430 kohm, and 110 ohm. We still weren’t sure how the transistor worked though; this was, by far, the trickiest part of the circuit. There were three leads coming from the transistor and we had no clue why. After searching online and reading in the book, we found that the three leads were called the collector, the emitter and the base. Now we were ready to start sketching a diagram to see how the circuit actually worked.
We first attempted to sketch the diagram from the prongs. We were able to draw much of the beginning of the circuit this way. It appeared that the 110 ohm resistor was in series with the parallel combination of the 330nF capacitor and the 1Mohm resistor. That was a little confusing because I had assumed that the capacitor would be in series after the bridge rectifier as in a capacitor-input filter. After a few attempts to sketch the rest of the diagram, we decided to use Multisim. Multisim was a very useful tool. It allowed us to use all of the components on the circuit, and, through trial and error, create a circuit that worked. Once we were able to recreate the circuit, we could break it down