Arduino + Sparkfun 6.5 in display

[rovduino]

Would someone be willing to help us figure out the best way to interface this display with the arduino? its common anode, so a number of the ideas we've had wont work. Based on several similar posts, the chips are not relevant to our project or are no long available. Shift registers are not necessary, a darlington transistor dip package would be sufficient. a schematic would be greatly appreciated.

heres a link to the display:http://www.sparkfun.com/products/8530

[hexskrew]

Here is someone's blog that posted a how to on sparkfun:
http://deleteaso.com/2-sparkfun%E2%80%99s-7-segment-red-65%E2%80%B3-display-and-arduino/

[rovduino]

We saw that. That chip is not available.

[hexskrew]

Here is an alternative. Just use switching transistors along with a standard shift register. Same effect, just a little more to it is all.

*I have no idea if these shift registers are connected properly to each other or the arduino. I do know their outputs are wired properly to the switching transistors though*



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[rovduino]

instead of using individual transistors, could i use a uln2003a or simlar in order not to have the wiring mess? and with the method posted, could i bypass the shift register and individually control each part of the led with a transistor?

[hexskrew]

Yes you could use that darlington array to bypass all the clutter (however a 15 pack of transistors is only like.. $4.50 at radio shack), but would definitely help in the wiring process.

Now you can sort of... bypass the shift registers, but you'll still end up having a wiring mess on your hands cause you will effective be going from 6 outputs on an arduino to well... you don't have enough outputs on your arduino to accommodate all the wires..

Wait scratch that. YES! Actually using one of those darlington arrays, and TWO transistors, you can cut the clutter in 1/2.

Wire all inputs (well negatives from the displays) together so you only have 1 wire per input for both leds. Now for those inputs, wire each of the 8 inputs to the darlington array.

And you will need two transistors to switch the VCC voltage for each display. This way you just constantly write to each of them at one time. You shouldn't really notice any flicker with this setup. More than two displays however, it could get ugly.

[rovduino]

We only plan to use one display, so all should work out well. i assume we can cut out the 2 transistors used for switching.

how would i wire the display? the 12v common on the display i understand would just connect to my 12v rail.

i assume that #C would be the individual ground pieces of the display. emitter on the chip would go to ground? leave com open?

[hexskrew]

Man.. If that chip only had logic that thing would be super sweet.

Unfortunately it actually does not have any logic as it's a 1 to 1 bit for bit transistor chip (i.e. your still using one output on the arduino to control one output on the chip).

But with this chip, and using only one of the signs, it will be VERY simplistic (and hardly no wiring at all).

Here's a schematic:


HOLY CRAP!!! HAHA! I made a schematic for daisy chainable led backpacks to use with it

Needs a few clarifications, but with some simple code and one or two more small components, MAN this would be a great, cheap alternative to the $59 Master controller: http://www.sparkfun.com/products/9462
and accompanying $27 slave controllers : http://www.sparkfun.com/products/9463

[rovduino]

We have our parts on order... thank you very much for your help. 

[rovduino]

What resistors did u calculate for the led part of the display?

[hexskrew]

Actually it doesn't really matter in my setup, because the resistors actually have more to do with the transistor operation than anything. (just that one side needs to have more than the other)

[rovduino]

so with the uln2003a chip, does it require a base resistor? with the darlington transistor, it shouldnt... the display needs them... what values would you recommend?

[hexskrew]

the uln2003a chip has it's own built in resistors, but as per this info in the datasheet:

SEVEN DARLINGTONS PER PACKAGE.
OUTPUT CURRENT 500mA PER DRIVER.
(600mA PEAK)
OUTPUT VOLTAGE 50V.
INTEGRATED SUPPRESSION DIODES FOR.
INDUCTIVE LOADS
OUTPUTS CAN BE PARALLELED FOR.
HIGHER CURREN

Found here: http://www.datasheetcatalog.org/datasheet/stmicroelectronics/5279.pdf

I think this wont even be a drop in the bucket for the uln2003a, however honestly.... I don't know what transistor rating to use for the actual led display. I would consult westfw. He would know. I am still getting into the whole deal.

[Devicemodder]

i used 7 bc547 transistors with the emitter to a segment and collecter to ground base to ard pins and common anodeto 12v use a 7812 for display

[rovduino]

what resistors did you use on the led segments? or did you at all?