In this section of the course, we are going to build a Vactrol based VCA with our knowledge of using opamps. Here we will use a Vactrol as a resistor but where we can control it with the voltage. (from a LFO/envelope generator)
Now we are going to drive(lighting up) an LED. Unlike resistors, LEDs has polarity. Which means they have + and - pins. You need to feed the current from one end to other. See below:
The longer side is “+” and the shorter side is the “-”.
You need provide a minimal voltage across these pins. For a green LED it’s about 2V. But this can go down as 1.8V too.
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But you cannot connect these LEDs directly into a voltage source (assuming it’s higher than 2v).
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If you connect it directly, the LED tries to get the as much as current from the power source and eventually it will blow up. (May be, this is good experiment for you to try). That’s because an LED can only take upto 10mA of current. In our bread modular setup, you can get up to 150mA of current.
So, we need to limit the current with a resistor as shown below:
As you can see in this case, the 1k resistor limits the current. If you measure it, it restricts the current to 1 milliamps (1mA). It’s more than enough for an LED to light up.
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Try changing the 1k resistor with other values and see whether is there any changes in the LED brightness.
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<aside> 💡
measuring the current it out of the scope for this course. But it’s very simple. Checkout this ChatGPT thread for that.
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Have a look at the following:
