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Topic: Is there a better way to control 14 LEDs other than a shift register? (Read 1 time) previous topic - next topic

tdawe

I'm looking to build an RPM display for a motorcycle that will display a row of LEDs (14 in total), one for every 1000 RPM from 0 to 14,000, and to possibly have all LEDs flash at RPMS>12,000

My current plan is to control them using two 79HC595 Shift Registers. Since (as I understand it, since I don't have a data sheet for my cheepo LEDs) they will draw too much current when they are all on my plan is to cycle them on and off at 10ms intervals, so that they would all appear on, even though only half would be lit up at any one time.

I've tried to look to see if there is a better alternative, but everything I find for LED lighting strips they don't seem to be able to do what I want to do.

Does anyone know if there is a better product out there or am I going to be soldering individual LEDs? \

CrossRoads

Leave them on all the time and just higher current limit resistors.
Or, use TPIC6B595 to sink current thru the LED and allow full 20mA to any LED at any time.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

CrossRoads

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

PaulRB

How about 5 Arduino pins, 4 npn transistors (e.g. bc337) and 5 series resistors? (In other words no shift registers or other chips).

Paul__B

Get serious!

A MAX7219 will control any number of LEDs up to 64, provides complete current control, requires two bypass capacitors and a current control resistor, and is controlled (exactly like shift registers) by three Arduino pins.

Why do it any other way?

And talk about cheap!

PaulRB

If the OP wants to extend the project to include a 3 digit speed indicator and a 1 digit gear indicator as well, i would absolutely agree max7219 would be the way to go.

Paul__B

Either way, the MAX7219 (or various other ICs, but this is probably the most readily available) is a neat single-chip, optimal performance (i.e., bright) solution.

guix

Also TLC5940 can be good for what you need: 16 channels, only one current limiting resistor needed, 12 bits PWM... and it's cheap as well.

tdawe

Thanks for the replies,

You sold me on the MAX7219, I'm always a sucker for the argument of future expansion potential.

UtahJarhead

You can do it with 2 pins plus power if you use ws2811, ws2812, ws2812b (any of them will do the same for your purposes).

LMI1

MAX7219 is a neat chip, if I wanted to show numbers, but for just 14 separate LEDS, I would connect them directly to the CPU, with current limit resistors of course.

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