12/12/2023 0 Comments Arduino led voltage![]() ![]() The voltage available to drive your LED from a digital output is the difference between the voltage on the digital output pin and the forward voltage of the LED. Higher power LEDs will take more current, but then its better to use a ready-made LED driver chip. for a light show, modern LEDs work very well at currents of 2-10mA, and a maximum of 20mA. (See below for limit of consumption on output ports.) What current do you need?Īssuming you are using the LEDs as indicators, rather then e.g. While common 3mm and 5mm leds CAN be run at 20mA and more, a maximum of 10mA is generally sufficient, and limits your consumption, especially if you have several inicator lights. Inexpensive green LEDs are MUCH less efficient than red - yellow ones, and need a higher current if their intensities need to match. ![]() NOTE: for use as indicators indoors, red, orange and yellow LEDs AND also blue and white ones are typically acceptable at currents of about 1mA. I measured the forward voltage of some cheap LED's at a current of 10mA 3mm and 5mm sizes showed the same values. If we connected 8 LEDs drawing 20mA each to a single port we could be drawing 8*20mA = 160mA. We also need to bear in mind the electrical characteristics of the arduino chip each output is capable of sourcing or sinking 40mA however "the maximum current for each I/O port should not exceed 100mA". You can see that LEDs in the "warm" end of the spectrum only need low forward voltages, while some types in the "cool" end - green onwards - may need over 3.3V so you could not drive these directly from a 3.3V model arduino. If you need precise values consult the data sheet for the device you are using. Its compiled from various manufacturer's data sheets. Here is a table (Table 2) showing the forward voltage for different LEDs in the common 3mm or 5mm package. If you want to know how these were calculated, read on. The table above gives some "rule of thumb" figures. Table 1 - the "right" resistor value for your project - values for use in daylight:įor use as indicators indoors you can even use resistors up to 10k to minimise power consumption. Vf in turn depends on the colour of your LED, and the materials used to make it. It depends on (1) the supply voltage, (2) the LED forward voltage, Vf and (3)the current you choose to run through the LED. However if you are driving a lot of LEDs you may wish to use more appropriate values as explained below.Ĭhoose the right resistor value for your application I'm often asked "what is the right value resistor to drive an LED from a digital output on the arduino". Note that if you are using style 2 the LED current also flows in the arduino GROUND line (see Grounds)Īs a starting point a resistor of anywhere between 470 ohm - 1k will be suitable. The box in the diagram is just depicting a single arduino digital output pin.ġ: Here the LED and resistor are connected between the output pin and GROUND.Ģ: Here the LED and resistor are connected between the output pin and Vcc.Įach has its own advantages and disadvantages. In either case you need a series resistor to limit the LED current. Choose the right resistor value for your applicationĪn LED is connected between the arduino output pin and EITHER the +Vcc supply, or the arduino GROUND, as shown in this diagram. ![]()
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