Simple Light Switch

In building Simple Bots, we are going to use a series of photo-coupled devices called modules. But, before we can do this, we need a good photo-couple to use as a light-activated switch. To make one of these switches, we will be using a special OSRAM-brand photo transistor and any standard NPN transistor (like a 2N2222, 2N3904, BC546, etc.). These switches will allow the motor to spin in direct correlatoin to how much light it senses. In other words, the more light, the faster the motor goes and the less light, the slower.

Step 1: Go Get Stuff

You will need:

(x1) OSRAM-brand photo transistor
(x1) NPN transistor

Step 2: Line Up

Lay the phototransistor atop the NPN transistor such that the base of the NPN transistor aligns with the emitter (longer leg) of the phototransistor and the collector of the NPN transistor aligns with the collector of the phototransistor.

Step 3: Twist

Twist together each lined-up pair of NPN transistor and phototransistor leads.

Step 4: Solder

Solder together the connections of each twisted pair of transistor leads.

Step 5: Trim

Trim the middle pair of wires such that it is shorter, but the connection between the base of the NPN transistor and the emitter of the phototransistor remain soldered together.

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