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Topic: difference in current when displaying 1 and displaying 8? (Read 4198 times) previous topic - next topic


You could import them:


also found some in your part of the world:


or you could make them up from strips of leds:


Don't know how far you are from this store, but they seem to have a few branches.


Nov 11, 2013, 11:23 pm Last Edit: Nov 11, 2013, 11:27 pm by arduinodlb Reason: 1

Just 1 point.  The battery is 12V, 2 AH - Ampere-hour, which means it could supply two Amps for one hour (although you really should not make it do this as it would not be good for battery life - you should limit it to one amp.)

Good point. Thanks for pointing that out Paul. I was going on the original poster's comments and should have checked. Especially for Batteries which are only ever in AH.
Do not IM me. I will not respond. Ask questions in the forum.


Quote from: calvingloster

... the learning curve is just so steep haha!

The curve is as steep as you set it.
Lower the bar a bit so you can keep an overview if necessary.

I know different color LEDs have different forward voltages.
And different LEDs have optimum performance at different currents.
That's exactly why i told OP to check datasheets.
Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html


What do you mean by "You may well need to use drivers which themselves control the current" ?

Since you are requiring currents greater than the ATmega chip can provide, you are going to need transistors (or one or more driver ICs designed for the purpose) to drive these LED arrays.  I was meaning constant current drive circuits in which the transistor rather than simply a series resistor is used to regulate the current.

For example:

Some driver ICs - which also may include shift registers to make interfacing easier - provide such a constant current drive.


You can use TPIC6B595 shift registers to sink current thru the strings of LEDs that make up your segments.
Each 12V powered string, generally 5 LEDs, maybe 6, will require up to 20mA.
Each output of the TPIC6B595 can sink 150mA, so you can have 2 or 3 strings arranged to be as long as you want the segment, or strings next to each other for fatter/wider segments, and each shift register output can still handle 1 segment.
You'd then have a shift register per digit.
This board I make has 12 shift registers, fully populated it could do 12 digits. No multiplexing required, so the digits are nice & bright all the time.

Here's another that supports just 4 digits - you don't have to add all the extra parts (3.3V regulator, SD card socket, RS232 driver, or even the screw terminals).
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.

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