We worked with phototransistors today in lab. It is basically a photodiode amplifier combination that is integrated on a silicon chip. Recall that a transistor has an emitter, collector, and a base pin. Notice how this device only has two actual pins. THe third pin is the base pin, which is actually in the device already. The light (light that the sensor detects) is the base activating pin for the device. This device is going to detect IR (InfraRed). That is light that we humans cannot see, but our phones can! well, some phones; Apple phones cannot see that light, but the Android phones are able to display IR light on the camera screen.
Time permitting, we did not light a candle for flame (too messy as the wax goes onto the floors and makes a mess, and a fire hazard). We used a pre-constructed flame which is a couple of IR LEDs on a breadboard [piece that outputs IR light.
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| Phototransistor |
Once again, due to time permits, I built a circuit on the breadboard to detect IR light. It is only one phototransistor, and One carefully chosen resistor. That resistor, depending on its value, will allow more or less voltage/current to be ran through it. The important concept in this is the preferred gain range. We want a resistor, so that when hooked up to the phototransistor, we got a high value of 1000 or so on the display with super intense IR light. The lowest we should see is around 20's when the IR light source is about 4 feet away from the sensor.
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