Up to 70 LEDs on one digital output

Using Arduino LEDs and Multiplexing
1

Hello,

I am looking for fast help. I need to connect up to 70 LEDs connected in parallels(and I can't change that) onto ONE digital output and use PWM on it. I've seen that max. current for digital output is 40mA, but I measured those 70 LEDs spent about 330mA connected to 3.4V power supply.
I need to make this until tomorrow, so I hope circuit will be with some simple components.

2

You need 70 suitable resistors (one for each LED) and a transistor that can take the current. Assuming you have to work with 3.4V, you will need a transistor with a very low internal resistance, preferably a MOSFET with just a couple of mOhm. If you have 5V available, just use a simple 2N2222 with about 270Ohm base resistor.

3

I am making a very similar circuit. Attaching 3 LEDs in parallel and uses 9 columns of these to make a 3x3x3 cube. Problem is I cannot attach individual resistors to each LED. Hence, is there a solution whereby I can use 1 resistor for every 3 LEDs in parallel, use a transistor to supply approx 60mA of current?

4

No.

5

emceepaul:
I am making a very similar circuit. Attaching 3 LEDs in parallel and uses 9 columns of these to make a 3x3x3 cube. Problem is I cannot attach individual resistors to each LED. Hence, is there a solution whereby I can use 1 resistor for every 3 LEDs in parallel, use a transistor to supply approx 60mA of current?

You might be able to get around this,
I use LED's a lot for de-bugging so I made it easier by cutting off the anode really close to the LED and carefully soldering a 1k resistor to the anode stump. ( trim one side of the resistor so you have just enough wire to solder. )

You could use this same method in your cube.

6

madworm:
You need 70 suitable resistors (one for each LED) and a transistor that can take the current. Assuming you have to work with 3.4V, you will need a transistor with a very low internal resistance, preferably a MOSFET with just a couple of mOhm. If you have 5V available, just use a simple 2N2222 with about 270Ohm base resistor.

I've did this and successfully drove my LEDs to light up. Thanks a lot