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'is there any pic with LED driving capablity?'
1998\01\26@132212 by sam Haile

picon face
please email me back if you know any pic which can drive lED directly I
am not aware if such pic does exist.

sam

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1998\01\26@155936 by Morgan Olsson

picon face
Almost anything can drive a low-corrent type LED (about 1-2 mA required)
A lot of PICs have some especially strong outputs, like the PIC14000 I«m
using.
Select one you think you can use and RTFM.
/Morgan


At 10:16 1998-01-26 PST, you wrote:
>please email me back if you know any pic which can drive lED directly I
>am not aware if such pic does exist.
>
>sam
>
>______________________________________________________
>Get Your Private, Free Email at http://www.hotmail.com
>
>

Morgan Olsson, MORGANS REGLERTEKNIK, Sweden, ph: +46 (0)414 70741; fax 70331
============================================================================

1998\01\28@072539 by Morgan Olsson

picon face
>>>> Almost anything can drive a low-corrent type LED (about 1-2 mA required)
>>>> A lot of PICs have some especially strong outputs, like the PIC14000 I'm
>>>> using.
>>>> Select one you think you can use and RTFM.
>>>I am trying to understand the Port C capability of "Direct LED drive"
>>>in the PIC 14K manual. It seems to be rated the same source/sink as
>>>the other ports. What exactly do they mean?
>>>
>>Good question. In the detaild port description (DS40122B-page 30) it
>>says Port C 5:0 can drive LEDs. No other Port description tells that.
>>But in the electrical characteristics section they only specify different
>>(lower) current for RC6, RC7, RD0, RD1, OSC2.
>>All other output pins specified to 0,6 V drop when output high @8,5mA
4,5V Vdd.
>>So the same document tells two different things!
>>(I also found other things in >>this manual strange,
>>undefined or double defined, but it is still preliminary, so...)
>>Other manufacturers specifies LED capability when they can drive 20mA.
>>So, are the LED outputs that strong (20mA), and just forgotten in the
electrical
>>characteristics section?
>>And are they assymetric like all other, (sink much stronger than drive)?
>>/Morgan

>I was hopeful that they had some type or current limit that would let
>you drive LEDs with no resistor.
>
They don«t.
A while ago, however, I used CMOS hex inverter 4069U to directly drive
LEDs. Theu are weak (deliver 3-5mA I think) but suitable for small LED
indicator. I beleive it was even within the manufacturers spec to to so,
but I don«t remember which.

Maybe the PIC don«t risk get damaged either? (This of course depends
strongly on supply voltage) PIC:s are much weaker in pullup than sink, so
maybe using them to pullup?

Under maximum ratings they specify (looking at C84) max sink on a pin to
25mA, and source 20mA. (OBS there are also max limitations for a ports
total current)

At 4,5V supply volt the C84 have a max loss of 0,7V@3mA=233ohms.
If the LED need 2V, the loss of the pin = 2,5V
2,5V/233ohms=11mA.  Nice.
BUT BEWARE:
1)      0,7V@3mA is minimum drive of the pin. They don«t specify how good a PI
C
can be at best. In this case a strong low-loss output will maybe make to
much current, so it will get damaged!
2)      The resistance is lower at higher voltages so the current rises quickly.

For LED drive I recommend using PIC to sink, and series resistor.

However, when using the A/D cirquitry in PIC14000 Vss current causes
measurement ofset, so then use PIC to source instead!
/Morgan
Morgan Olsson, MORGANS REGLERTEKNIK, Sweden, ph: +46 (0)414 70741; fax 70331
-

1998\01\28@203626 by TONY NIXON 54964

flavicon
picon face
There are LED's around that have an internal resistor built in. They
run directly from 5V. Check out the Farnell catalog.

Tony

For the beginner....
PicNPoke Multimedia 16F84 Simulator Assembler, and Tutorial.
Now with PicNPlay circuit simulator.
Plus animated Address Mode Tutor.

http://www.dontronics.com/picnpoke.html

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