Build and test the receiver

- [Voiceover] We're gonna start by building the receiver system that takes the light into the solar cell, turns it into an electrical current, and goes into the amplified speaker. So, let me bring in the amplified speaker. Now, many amplified speakers exist. You normally plug them into your electronic device to make it louder. And I'm going to add to that amplified speaker a solar cell. The solar cell takes light in and converts it to an electrical signal. Now, on the back of the solar cell there are two leads. And I'm just gonna clip the alligator clips to those two leads. It's an alternating current signal so I don't care which one is connected to which side. The one tricky bit about this assembly is the use of this mono phono jack, a mini phono jack, but it's monaural. It's not stereo. The mono one has just one black band on it. The stereo one will have two black bands. And the thing is that a mono phone jack works in all applications, whereas a stereo one will not work if you have a monaural system. So this is the universal, it always works, plug. So when I plug the solar cell into the amplified speaker and turn it on, I can hear the buzzing of the room lights. Room lights actually get brighter and dimmer with time, and they make a little buzzing signal. That's a good way to test that your circuit is working. Now, I have another light here. This is just one of those squeeze on light emitting diode lights. And if I shine that onto the solar cell, you'll find out something you didn't know, which is that this light is actually going on and off, creating a buzz. It also has another mode where it blinks. And each time the light hits the solar cell, it makes an electrical current that pushes that speaker out and you can hear it as a click. Light turned into sound.