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Topic: current source 16x12 led matrix (Read 3956 times) previous topic - next topic

Hans420

Hey guys,

After a few small scale arduino projects I'm in the preperation of making a LED matrix for a project.
I've done some research and basicly I think the plan is the follow:

Send serial data from Arduino to 2 shift registers (74HC595) which in turn are connect with the rows of the matrix. The colums are connected to resistors and then ULN2803 driverarray's ( http://www.produktinfo.conrad.com/datenblaetter/150000-174999/171824-da-01-en-IC_ULN2803_DIL18.pdf ) which are  driven by some more shift registers.

From what I understand this will let me turn on the led's one by one.
My question is first of all will these driver array's survice for sinking the current (and are they arduino compatible firstmost)?

And second, I'm looking for an IC to source the current (same way as the ULN2803's sink it) so I could use and external power supply. And correct me if I'm wrong this will make me turn on the matrix per row, thus speeding up up the process and allowing me for brighter light.

All help will very much be apreciated!


CrossRoads

Use cd74AC164 instead of 74CH595 as the anode drives of your matrix.
Has 24mA output capability vs just 8mA for HC595.
12 x .02 = 240mA, ULM2803 can handle that.  Or, use TPIC6A595 for combined shift register/current sink and cut a couple parts out of the design.  Shift data to them just you would HC595.
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.

Hans420

Thanks for the quick reply! Not really getting how 24 mA output capability would be enough for the 240mA I need to lilt the row of LEDs?

Wouldn't a sourcing transistor array (is this a thing?) be the best solution? (incl ext power supply)

Hans420

http://www.instructables.com/id/LED-matrix-using-shift-registers/step3/The-control-hardware/

According to this guy mic2981 (or UDN2981) would be alright?
http://hackerstore.nl/PDFs/UDN2981.pdf looks quite alright to me eh?

PaulRB

#4
May 28, 2015, 11:29 pm Last Edit: May 28, 2015, 11:32 pm by PaulRB
Not really getting how 24 mA output capability would be enough for the 240mA I need to lilt the row of LEDs?
CrossRoads is saying that the '164 could provide up to 24mA per led. 2 x '164 could provide 20mA for each of the 12 leds in the columns.

Wouldn't a sourcing transistor array (is this a thing?) be the best solution? (incl ext power supply)
Yes, but hard to find and all seem to have quite a large voltage drop. Better to have the transistors on the "sinking" side (the cathode columns). This is what the tpic chips mentioned would provide.

Paul

Hans420

Okay but this would mean i'd scan column by column? if the anodes are connected to the rows and columns to the cathodes?

PaulRB

What's the difference? Rotate your matrix by 90 degrees and columns become rows. But its easier to find chips that will allow you to scan by one group of cathodes at a time.

CrossRoads

Quote
Okay but this would mean i'd scan column by column? if the anodes are connected to the rows and columns to the cathodes?
Yes.
You were thinking the other way? Then buffer the anode shift register with this part
http://www.digikey.com/product-detail/en/MIC2981%2F82YN/576-1158-ND/771627

Then I guess you would have an array of 12 int's to hold the data to be displayed.




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.

Hans420

#8
May 30, 2015, 03:38 pm Last Edit: May 30, 2015, 03:55 pm by Hans420
Yeah I was thinking the other way around and somehow switching this didn't catch my mind, I guess I'll be fine then thanks alot!

Okay just for the sake of being sure, the resistor will then go on the anode* side of the matrix right?

PaulRB

the resistor will then go on the anode* side of the matrix right?
If you are talking about sourcing current for the anodes with the 74hc165 and sinking from the common cathodes with the tpic6b595, then yes, put the series resistors on the '165's outputs.

abhijit2683

Hi All,

Can anybody provide the detail description and schematic for the above circuit.

pls help :)

Thanks
Abhijit

CrossRoads

cd74AC164 (high current shift out register), not HC165 (shift in register).
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

This is 16x16, build up less for 16x12. Anodes driven by cd74AC164 (24mA outputs), cathodes by TPIC6B595 (150mA outputs). Each column turned on for
(1/30 sec)/# of columns.
Say 2mS for 16 columns for flicker-free operation (2000uS).
Expand as needed.
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.

abhijit2683

Thank You very much @CrossRoads :)
Sir ,can you please provide the sample code as I am newbie with matrix and Arduino.

Regards,
Abhijit

Hans420

I can't really find a CD74AC164, my store does have the CD74HC164 tho, will this one suffice?

http://pdf1.alldatasheet.com/datasheet-pdf/view/27016/TI/CD74HC164.html

looks quite alright to me, eh

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