This is another one of those circuits I wasn’t too happy with; there are a lot of those with the way this kit does things, it seems. I can understand the logic: Just dive in, and we’ll fill in the missing bits later. For now, just build the circuit and have fun. I’m just not that sort of personality, I guess. I’d prefer to have any component we’re going to use explained to me first. Still, though, I suppose that’s part of the experience. Here’s today’s circuit:
We’ve got two 100uF capacitors, wired in parallel, A 22 kilohm resistor in parallel with those, a 10 kilohm resistor, a 4.7 kilohm resistor; To the right of the 10 kilohm resistor is a component we’ve not talked about yet; the kit book makes no mention of it or what it’s doing. It’s the symbol that looks like a triangle with a line underneath it. That is a diode; A diode is a component that conducts current in only one direction; Ideally, it has zero resistance in one direction, and infinite resistance in the other. (In reality, this isn’t true, but it gives you an idea of how it works.) Diodes have many uses, especially when you want to control the flow of current so that it goes in only one direction. I suspect that this one is being used for over-voltage protection, that is, to keep too much current from flowing into the component the diode’s bottom terminal is connected to; One we’ve seen before when the kit went off into la-la land, the transistor, remember, that’s the symbol that’s the circle with the network of lines inside it. When we talked briefly about transistors before, we discussed how they can amplify and/or switch electronic signals. I think this one is acting as a sort of switch. Also in the circuit, you see the relay, a power switch, and a 9VDC battery power supply. So, what the circuit is doing is demonstrating that capacitors can take some time to charge. When the power is turned on, the capacitors begin to charge, when they accumulate enough charge, they cause the transistor to act like a switch, sending current to the relay, which clicks. This circuit is using the relay as a noisemaker, like we saw in some earlier circuits. Here’s what it looks like all built:
So, what’s the demonstration like? Here’s a brief video I made of it:
When I turn the switch on, you hear the loud click of the switch, and then almost immediately after, the softer click of the relay. The shortness of the delay makes this circuit even more disappointing. It doesn’t prove to be a great demonstration. Still, though, you get the idea, sometimes capacitors take some time to charge. If you’ve ever used an older camera, where you had to turn it on, and wait a minute or two for the flash to charge (usually punctuated by a high-pitched whining sound from the capacitors in the charging circuit), that’s what was going on. There are scenarios, as you might imagine, where a delay in capacitor charging could be used on purpose, as a sort of timing circuit, as the title of this experiment implies. I’ll leave you with this thought exercise: How could we make the charging take longer? Use higher farad capacitors? add a resistor to limit the charging current? Think about it. Feel free to post your thoughts in a comment.
OneCircuitADay 