So I'm working on a project for school and I need to wire 36 leds together on one digital pin. I was thinking about using a transistor to up the current. I'm having trouble deciding which one to use. Does anyone have any ideas on what I should do?? Thank you!!
Welcome to the forum
What type of LEDs are they ?
Are they all going to turn on and off at once ?
Assuming they are all controlled together with one transistor, the main thing is the transistor's current rating.
Usually the current rating assumes that the case is held at room temperature so give yourself some safety margin and "derate" the transistor and if it's too hot to touch add a heatsink.
A Darlington transistor (two transistors in one package) has more current gain and it won't require as much current into the base (from the Arduino). Or a MOSFET essentially requires almost no current from the Arduino, but it has to be a "logic level" MOSFET in order to be turned fully-on by a 5V signal.
If you have more than 5V "handy" you can wire 2 or more in series to "share" the same current and th same current-limiting resistor and your transistor or MOSFET doesn't have to handle as much current.
@UKHeliBob @DVDdoug , so I have this 3D printed box with letters. The letters are made up of small circles which the LEDs slide into. I also have an LCD screen and push button. The user will push the button, each word will light up and then they flash in sequence. There are 4 words and each word will have its own digital port. I have exactly enough digital ports to fit everything in I'm just concerned I will fry the Arduino because it can't supply enough current. The LEDs are 20mA and 3v so like standard LEDs. Thank you for the help by the way!
What processor are you using? I am assuming they are all turned on and off together because of the one pin. When looking at output drivers there is also the voltage drop across the output device. MOSFET will be the lowest maybe ~0.1V, A transistor 0.7V, and a darlington transistor 1.4V. What color is the LED and its forward voltage drop. Is there more than one color? This voltage drop times the current will give you the wattage the device needs to dissipate. How are you going to connect them, series, parallel or both. What voltage do you have available to operate them, the higher the voltage the fewer resistors will be needed. A LED is a current device, not a voltage device but it needs a color dependent voltage to turn on. More information will help us help you.
I'm not sure what you mean by processor. I'm using the Elegoo Uno 3 board. Each word is going to have its own digital pin. The words are " I Love Electrical Engineering," so each word is made up of LEDs the most one word has is 36 LEDs. I was going to wire them in parallel but if wire them in series easier, then I'll go that route. Once the user pushes the button all of the words light up then begin to blink in sequence. Also, the LCD screen shows a message. The colors are white and red for the LEDs. I have access to 5V for each digital pin. On top of that a 5V port as well.
Have you considered multiplexing? It's not the best... but it works!
You only would need 12 pins... less than 36 but definitely not 1 pin
Or use a led matrix. Still not 1 pin though.
Or NeoPixels! It needs only 1 pin and has different colors.
UPDATE:
I just realized that this thread was about transistors, but oh well.
Is the processor and it definitely has more than one pin as you stated in your original question. I think the next thing you need to do is generate a simple schematic neatly drawn by hand is good, as to how you want to wire this, this will affect all aspects of your project. You can get KiCad for downloading it, it is actually a full CAD program. I as still waiting on what voltage(s) you have and how much current they can supply (hint you need to know what the 36 LEDs will draw).
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