MAX7219 8-digit LED Driver driving darlingtons for high current

Scarecrow

Hi guys!,
·As ive seen you hear a lot in this forums, im not too much of an electronics guy so ill be asking some dumb questions from time to time · anyways ill try my best to look for an answer in the forums & internet before posting...just wanted to get that off my head in my first post hehe.....

ok now heres what ive been thinking of:

i want my basic stamp to use the MAX7219 led driver to control up to 64 darlington arrays· (is that possible?) if it is possible i would like to see maybe some examples of diagrams to do it and maybe some info on current values from the led driver and some darlingtons types, i would try to help also on this matter but i need some help from the experts! hehe

well thanks in advance!!!

kb2hap

Sorry but the info in your question was far too vague to give a good answer.

What are you trying to do exactly?

So it looks like you want to cascade a few of the max ic's to control 64 outs or 64 darlington arrays?

the uln2803 darlington arrays outs can handle about 500ma each.

if all your looking to do is control a bunch of outputs the it would be much cheeper if you used 74hc595's the max ic's are around $10ea and the 595's are only about a $1 each.

here is a link to the stampworks manual which has some good info on expanding outputs:

http://www.parallax.com/dl/docs/books/sw/exp/sw23a.pdf

http://www.parallax.com/dl/docs/books/sw/exp/sw23b.pdf

here are some links to the datasheets

http://pdfserv.maxim-ic.com/en/ds/MAX7219-MAX7221.pdf

http://www.fairchildsemi.com/ds/MM/MM74HC595.pdf#search='74HC595'

http://www.st.com/stonline/books/pdf/docs/1536.pdf

sleep on that info and get back to us.

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DTQ

Scarecrow

ok so basically i want to power a bunch of lightbulbs and motors arround 500ma each....

what i want is to use 1 of the max ic to get 64 outs since a single one can control 64 segments and utilize those segments outputs over some darlingtons because i need arround 500mA at least for each output

i looked a bit to the links you sent me and i·think i saw the·595 has a limit of like 35ma per output so i would still need to use darlingtons there right?, anyways ill look over the links tomorrow, today im just lazy in the pc and its already too late hehe. anyhow thanks a lot for your reply and thanks in advance for further replies

Post Edited (Scarecrow) : 3/6/2005 12:49:56 AM GMT

KenM

I don't believe the Max7219 will suit your application. The reason I say this is because the Max7219 multiplexes the outputs. When it is controlling 64 individual leds, ie., several 7 segment displays, it turns on one of 8 outputs, say·1~8 for example.

With·an output·turned on, '1' for example, it then enables the individual segments for the '1', it then turns off '1', enables '2' then enables the individual segments for 2, etc etc.

It does this rapidly to give the effect that all 8 (if used) seven segment displays are on at the same time, while in reality, only one is on at a time.

The '595's mentioned will suit the application well, 8 of them will do the job. And you correctly predicted, the 595's will not handle the current you want to eventually control, so yes, some darlingtons would be added to that, like the uln2803's mentioned.

k

kb2hap

yes you are going to have to cascade the 595's (8) then will will have to hook up the darlingtons to the 595's so you can get the high ma rating for all of the led's and motors
just make sure you have a power supply that can handle everything you want to do.
a few hundred milliamps a peice x 64 outputs adds up quick (if they will all be on at once, worst case scenario)
should be fairly simple to wire and will be a good coding project for you.

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DTQ

Scarecrow

ok ill guess ill go for the 595's it does looks like the best solution, thanks guys! =P also, are there any bigger shift registers i can get (like a 16 or even 32·outs one?, and what about the timings? i mean having 8 of them 595 will take some time to send the info to right? =P

also there would be rarely too many of them on at the same time but i guess its a good idea to have a power supply that can support the heat in a worst case scenario i dont want the project to turn into fireworks hehe

Post Edited (Scarecrow) : 3/6/2005 10:55:00 AM GMT

kb2hap

There may be larger shift registers but I'd have to look unless anyone else on the forum knows. The shift time I would not even worry about unless you had some really high speed stuff you were doing. Its very quick. but if you wanted you could allways do 595's on a few stamp pins and the rest on some other stamp pins. motors on some/lights on the others. to keep track of the controlling. but honestly you can do all 8 together. Someone on the forum has probably even done a time study on how long it takes to shift out to each register. you could check out tracy's site, he has done alot of timing studies with the stamp I'm not sure about 595's, but there is alot of good info if you dig through it.
I have definately seen timing studies on instruction times.

http://www.emesystems.com/

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DTQ

Scarecrow

wow that site has a lot of usefull info on the stamps!!!!!!!!! thanks for the site , hey could you point me in a direction for a brand or an ic number of a larger shift register? i have looked but there are so many different with different properties i wouldnt know wich to choose =(

kb2hap

well the shift registers I was pointing you to are serial in parallel out so they can really only handle by them selves 8 outs now check out this other chip see if it meets you needs

http://www.jameco.com/wcsstore/Jameco/Products/ProdDS/26171.pdf

its only $3

you may have to mix one of these for your led's and the 595's for the motors

along with the darlington or opto isolator

what are all of the currents you require?

it may take some playing around.

I used one of the above chips for 32 leds works great!

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DTQ

Post Edited (kb2hap) : 3/7/2005 1:07:18 AM GMT

Scarecrow

in fact im driving no leds, just lightbulbs and motors so thats why the need for more current, also im not completly certain of the current needs of each but the 500ma max for each is a good guess, also couldnt i just put the darlingtons along with that last mm5451?

kb2hap

Unfortunately, it sinks current so you'd have to use some sort of a buffer between the darlington and the mm5451. which doesnt make much sense. it can only sink 15ma so you'd have to use photo darlingtons or some sort of transistor.

So I think although it may seem like alot of work(wiring). I'd stick to the shift registers and darlington arrays. inexpensive,fairly easy interface, coding isnt so bad.

I'll keep looking to see if I can find anything else

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DTQ

Scarecrow

http://eshop.engineering.uiowa.edu/NI/pdfs/00/95/DS009587.pdf maybe? o well anycase if this doent do i would stick to the 595's hehe

kb2hap

Those look cool and they would do the job. They may add a little bit more programming.
but HOLY MOLY!!! $21each!!!

www.findchips.com
mouser

I dont know if cost is a factor
but you'd make out better getting the 595's
this chip would cut your count in half but I guess its more your call.

the 595's are between $.30 and $.80 each big difference

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DTQ

Scarecrow

o well i think ill go for the 595's but now the thing is where to find a good ic's supplier in switzerland or maybe in italy, france or germany...... any ideas? =S

kb2hap

well if you cant get digikey,mouser, jameco,arrow,or newark to ship over there you may have to do some good searching on the net

I looked online at this one search site
http://www.kellysearch.com/results.asp?search-text=Electronics&search-type=prodcat&search-location=qu&submit=Get+Digging

they seem to have elctronics suppliers in europe but some of it I belive was Danish
so I cant understand it.
but there may be somone else on the forum who shops in europe

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DTQ

Scarecrow

Ok, i found some good suppliers for europe in case any one wants the info:

http://www.distrelec.com/
http://www.conrad.com/

thanks a lot for all the help, ill be posting the results & toughts :P

Paul

Ahem, the SX48 has 36 programmable outputs. The SX52 has 40. I'm pretty sure they can drive a darlington.

My 2 cents
Paul