2

I need help correctly getting my parts list for a 7X6 matrix that will be part of a electronic outdoor scoreboard. Here is my parts list so far but I am stump whether the arduino is powerful enough to power these LEDS in a matrix.

  • 42 X Piranha Super Flux LEDS (~2.1 forward voltage) (~5000 mcd)
  • 4017 decade counter
  • 7 X 2N3904 transistors
  • 74HC595 shift register
  • 7 X 1KOhm resistors
  • 6 X 150 Ohm resistors
  • 4 X pushbutton switches (The matrix is going to be controlled by the 4 pushbuttons.)

I have the coding down I just need help setting up the arduino to power these high powered LEDS. If I am missing something from my parts list please let me know. Thank everyone in advanced! External battery will be used to power the LEDS.

This matrix will be powered by a 12 volt rechargeable lithium battery.

Marcus Gollahon
  • 21
  • 3
  • 1
    You say you have the code down, but I don't how that is possible if you don't even know how the circuit will be constructed. Do you have a schematic? How are the LEDs arranged? AVR microcontrollers can source/sink 40mA per pin, but only 200mA total at any one time. By "powerful enough" do you mean actual power sourcing for the LEDs, or just capable of controlling so many? – Kurt E. Clothier May 16 '13 at 03:46
  • 1
    Without providing a schematic of how you intend to wire up the design, it is not feasible to provide anything but general advice. Please add a schematic. – Anindo Ghosh May 16 '13 at 05:05
  • I am almost finished with the schematic, but taking Anindo's suggestions and replacing my shift registers. Thank you for your help. – Marcus Gollahon May 16 '13 at 12:48
  • If the Piranha's are white and if you have not bought them yet, look at the Nichia "Raijin" NSPWR70CSS-K1. It stomps the Pirhana into the dust and then eats it for breakfast wrt luminous efficiency. 160 l/W+ at low mA. About 125 at full current. Typical values. Also look at the newish Nichia NSDW510GS-K1 with about 40 degree cone angle and ... 570GS with wide 140 ish degree cone angle. Both are rated at up to 80 mA in a 5mm package (2 die in parallel inside) and are exceptionally efficient. Very nice parts. | Declaration: My sole involvement with Nichia is as a customer. – Russell McMahon May 16 '13 at 14:54
  • The LEDS are super flux red. – Marcus Gollahon May 16 '13 at 14:56
  • You MAY be able to get red Raijins - I've never checked. Very nice LEDs. – Russell McMahon May 16 '13 at 15:00

1 Answers1

2

First off, neither an Arduino's GPIO pins (as Kurt E. Clothier has pointed out), nor more relevantly the voltage regulators on board any standard Arduino board, can supply the amount of current required to operate 42 LEDs simultaneously:

42 x 20 = 840 mA is well beyond the typical 500 mA polyfuse on the Arduino's vUSB power rail. You would not actually come up against the microcontroller's own current limitations, since the LEDs are most likely not going to be driven directly by the GPIO pins, but by the shift registers mentioned in the question.

While the regulator on the board may be rated for 1 Ampere or more on some Arduino clone boards (the Ruggeduino comes to mind), drawing that much current will cause the regulator to overheat, and either shut down due to thermal protection, or get damaged.

On the other hand, given the bill of materials in the question, it seems a safe assumption that no more than one row of 7 LEDs is to be lit at a given time, in a multiplexed matrix arrangement. 7 x 20 = 140 mA is well within the capabilities of the typical Arduino board's regulator.

Consider replacing the 74HC595 shift registers with the Texas Instruments TPIC6A595 shift registers, which support 350 mA per output pin, and thus eliminate the need for the drive transistors. There are other slightly lower specification and lower cost shift registers as well, with high current rating and low output resistance, including the TPIC6C595 (100 mA per channel), if price is a factor.

The reason for this suggestion is not just cost saving on the (inexpensive) drive transistors, but the reduction of design complexity, and elimination of possible errors in wiring up that many additional components.

Community
  • 1
Anindo Ghosh
  • 50,188
  • 8
  • 103
  • 200
  • Would it be better to set up a separate power source? I planned on running this off of 12 Volt lithium battery. – Marcus Gollahon May 16 '13 at 13:47
  • @MarcusGollahon Yes, running the LEDs off a separate battery or power source would be a good idea, as the switching on and off of the LEDs will introduce voltage ripples into the power rail. Just ensure that the ground lines of both power sources are connected together. – Anindo Ghosh May 16 '13 at 15:34
  • The arduino's website states that the arduino can be accept a 12 volt from the battery pack. 7-12 volt recommended. So can my 12 volt battery power both at the same time. That will insure that the ground lines are both connected. – Marcus Gollahon May 16 '13 at 15:57
  • @MarcusGollahon Yes, that would work - assuming the battery doesn't suffer voltage dips below 6-odd volts when a number of LEDs are lit up. It's worth checking before you commit yourself, just to be sure. – Anindo Ghosh May 16 '13 at 16:16
  • I am thinking that I might be better off building a 7 segment display than a matrix with these high powered LEDS. If I use the TPIC6A595 shift registers could I possibly power 5-6 LEDS per pin on the register or just one led per pin? – Marcus Gollahon May 16 '13 at 19:35
  • @MarcusGollahon I've had 12 LEDs in parallel per pin on a TPIC6A595 without trouble. This is becoming a different question entirely, by the way. – Anindo Ghosh May 17 '13 at 01:25
  • Thank you for your help with this. I am wanting to order the parts soon. I need to know if this LED matrix using Piranha LEDs with a forward voltage of 2.1 V and a current of 20mA will be even feasible using just one 12 volt battery. I worry about the current and voltage being distributed throughout the matrix evenly. – Marcus Gollahon May 17 '13 at 19:45