# Experiment 9; MAKE: Electronics (2nd ed.)

#### minimaltom

Oct 3, 2022
2
Hi, im having a small problem with the capacitive coupling part of the chapter, that is experiment 9 and the 2nd edition. In figure 2-85 and 2-86 there is an LED and a 470 ohm resistor added beneath the 10k resistor. Its the 470 ohm resistor that's getting me. If you pressed button A it would seem to me that the capacitor would charge to 67% much quicker than 10 seconds because of the 470 ohm resistor which lowers the overall resistance of the circuit, being as the resistors are in parallel and this reduces the resistance of the circuit by half the sum of the resistors. is it something to do with the led only allowing the travel of current in one direction??

Thanks

#### minimaltom

Oct 3, 2022
2
Hi, im having a small problem with the capacitive coupling part of the chapter, that is experiment 9 and the 2nd edition. In figure 2-85 and 2-86 there is an LED and a 470 ohm resistor added beneath the 10k resistor. Its the 470 ohm resistor that's getting me. If you pressed button A it would seem to me that the capacitor would charge to 67% much quicker than 10 seconds because of the 470 ohm resistor which lowers the overall resistance of the circuit, being as the resistors are in parallel and this reduces the resistance of the circuit by half the sum of the resistors. is it something to do with the led only allowing the travel of current in one direction??

Thanks
Ok I've thought about it and reworded my question a bit.

Why have the 10k resistor in this circuit at all? Won't the capacitor charge itself fine through the 470 resistor? You don't need to measure the time the capacitor charges in this experiment and if you did wouldn't the 470 resistor alter the time it took to charge? If not is it because the LED only allows current in one direction?

Thanks

#### bertus

Moderator
Nov 8, 2019
2,797
Hello,

I have moved your question to its own thread, as the origenal thread is 10 years old:

Here is the picture from the make book:

There is a voltage drop accross the led.
At a certain point the led will go off.
That is when the voltage drop accross the led gets to low.

Bertus

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