Hello, I am looking for a relatively simple solution for driving 20 standard (20 mA) leds from AVR Attiny.
- I'd prefer to use some kind of IC (SIPO register?) or IC's instead of discrete transistors. It should be available in DIP package
- I want to use as low number of pins of the uC as possible - preferably serial connection
- It is may happen that all the leds will be lit at the same time so the components must withstand that.
Any recommendations?
lookup charlieplexing
Colin =^.^=
20 LEDS with tiny11
I'd use 74HC595's with ULN2803's for drivers. (3 x 74HC595 + 3 x ULN2803) Clock 24 bits serially from a pin, pulse the "latch" of the '595's and the '2803's provide the drive current for the LEDs. ... Donkey D...
Max7219. Overkill of course.
How about another uC ? That'll do the job nicely. 1 wire serial I/F for unidirectional data example.
Graham
A ULN for a *LED* !!!!! ???? Talk about total overkill !
Graham
of
ULN2803)
the
True, but they're cheap and will do the job.
... Little Steve
What's wrong with using the 595 outputs directly ?
Graham
You're right, (therefore I'm wrong) - I just had a look at the datasheet. I didn't realise that the '595 could source 35mA per pin. I thought the output current capability was similar to the 4000 family. My mistake.
... Donkey
That'll save a few bob !
Graham
datasheet. I
output
Yep - a stupid mistake on my part. Thanks Graham.
To the OP, (docent), FWIW:- Forget the ULN2803, but the 74HC595 is probably still the best way to go. (3 x 74HC595A)
... Donkey D... (Steve)
I would not use standard leds with 20mA but high briteness led that only need a few mA. Then you don't need the ULN drivers but can drive the leds with the 74HC595.
the
Hello Peter - although I didn't realise it when I first replied, the
74HC595A can source up to 35mA per pin, so a separate driver is not required even with standard 20mA LEDs. This was pointed out by Eeyore, (Graham).... Steve (alias Donkey D...)
... note the abs. max. Vcc/GND current rating of ~ +/-70mA.
Best regards, Spehro Pefhany
ULN2803)
and
only
required
Hello Sperho, that crossed my mind shortly after my last post. If more than
3 LEDs are lit at once, a driver will still be required. ( e.g. ULN2803 or similar) ... Steve
On the power pins ?
Since I rarely drive a led with much more than 5mA that wouldn't be a concern to me.
Graham
ULN2803)
and
only
the
required
concern to
Still, if the OP wants to drive 8 at a time with more than about 8mA each, a driver of some sort isn't a bad idea. ... Steve
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