SDIY Building Blocks

Appearance

LED Drivers ​

What It Does

Synthesizers love LED's! These circuits help you to light a LED properly.

Simple LED ​

We cannot directly connect a LED to power and ground. They always need some way to restrict the current. The most basic way is of course to use a resistor.

  • In actual circuits I always use small 3mm LED's. These are super bright and require much less current than in the Falstad simulator. I often use +12V(isch) with a 10k resistor.

Use buffers!

Unfortunatly, if you connect your simple resistor setup directly to a signal that signal will be influenced. If that signal is some sort presice control voltage or sophisticated audio, for instance, this is an issue.

Therefore, use buffers instead.

Transistor buffer ​

Schmitt trigger ​

  • Notice the Schmitt trigger is a logic buffer, thus the LED goes only on or off.

Non-inverting opamp buffer ​

Inverting opamp buffer ​

Constant current source ​

Comparator, bipolar ​

  • Notice the two LED's. This can be a bi-coloured LED.
  • The comparator is also a logic buffer, thus the LED goes only on or off.

Inverting opamp buffer, bipolar ​

  • Notice the two LED's. This can be a bi-coloured LED.
  • Control the brightness of each LED with the potentiometer.

Inverting Schmitt trigger, bipolar ​

  • Notice the two LED's. This can be a bi-coloured LED.
  • Notice the Schmitt trigger is a logic buffer, thus the LED's go only on or off.

VU-meter ​

The VU-meter converts an analog signal into a blinking LED array. Basically this works similar to a simple analog to digital converter.

Simple peak detector ​

Sometimes your signal levels are way too hot and might start to distort. If you want to prevent this use this simple peak detector that shows if you have signal levels above 10V, with just a LED, resistor and zener diode.

  • Notice the LED only lids up when the voltage goes above 10V (isch).
  • Zener diodes with different threshold levels are available. I believe 10V makes sense for a peak detector for Eurorack. Please play with the settings in the simulator and change the voltage threshold.