This basically depends on the LED color and main voltage value. A common problem dealing with LED is to decide which is the proper resistor size. The series resistor directly influences the LED current hence its emitted light intensity. How to size series resistor The LED equivalent model To avoid thermal drift, a LED shall be connected to a voltage generator with a properly sized series resistor. We can conclude that the resistor introduces such compensation which can limit current in case of thermal drift. Anyway, according to Ohm Law this lead to an increase of voltage drop of the resistor and subsequently a decrease of voltage drop on the LED which reduces the current flow. According to Kirchhoff Voltage Law, the total voltage provided by our generator is split between the LED and the resistor, i.e.Īs before, the current flow heats the LED causing an increase of free carriers and an increase of current itself. Considering the circuit in figure 2 the current flows from VCC across the resistor the LED reaching the ground. The simplest solution to this problem is a series resistor. By the thermal drift a LED can be permanently damaged. Applying a voltage across the LED, a current will flow in it now, due to its working principle, the flow heats the LED and this lead to an increase of free carriers which means an increase of current itself, and thus again an increase of temperature which leads to carriers increase and so on until the current in the LED is so high that it is permanently damaged.Ī LED cannot be directly connected to a voltage generator because it suffers thermal drift. The thermal drift A simple circuit to connect a LED to a voltage generatorĭriving a LED by voltage instead of current introduces some problems as LEDs suffer from thermal drift. Mind you, too much current would irreversibly break the device. Note that the higher is the voltage we put across the LED, the higher the current, the higher light intensity will be. We will explore those in a later article about light dimming.īasically, microcontrollers and other circuits work on voltage thus we will drive LED by voltage instead of current. It is important to notice that the LED light is proportional to its current and not to the voltage. To make the current flow in the right direction, the anode shall be connected to the positive voltage and the cathode to the negative. the cathode is the electrode through which the current flows out on a “through hole” LED, the cathode is the shorter wire.the anode is the electrode through which the current flows-in on a “through hole” LED, the anode is the longer wire.Like diodes, LEDs have an anode and a cathode: A LED is a diode which emits light when is fed with a current in a proper direction. I am quite sure you perfectly know what a LED is and how it works. Theory inside The Light Emitting Diode The scheme of a Light Emitting Diode In case you don’t, we have some good references here too ( Using STM32 GPIO with ChibiOS PAL Driver). You should know how STM32 GPIO peripheral works and how to exploit this flexible Input\Output controller with ChibiOS’ PAL driver.If you are not able to do that, you ought to take a look to From 0 to STM32, Developing on STM32: introducing ChibiStudio and A close look to ChibiOS demos for STM32. launch the tool-chain import, duplicate and create a new project flash and run and similar). You should have an STM32 development kit and be able to do basic stuff with ChibiStudio (e.g. To understand this article with proficiency you should match few requirements: Because of that, usually, every embedded development board is equipped with a LED marked as “User LED” and this means that it is actually connected to a GPIO pin you can drive via software. The LED can be considered the simplest peripheral output you can connect to a microcontroller. This article includes some simple examples to understand how to deal with LEDs when you are approaching STM32 and ChibiOS.
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