Microcontroller maximum current output... - Electronic Circuits Projects Diagrams Free

AceOfHearts · 9th September 2007, 03:32 PM

I have noticed that my 8051 can barely light an LED. I tried connecting the LEDs ground directly without a current limiting resistor, yet it was very dim.

I am using the 8051 to drive other devices like LCD which works fine.

Is the 8051 current output really so low?

I did 'overheat' the 8051 once by accudentally connecting it in reverse polarity... But the device still works perfectly.

Its just lighting an LED. So....

1) Is the 8051 current output always so low?
2) What is the best way to light up an LED connected to the 8051 to full brightness?

Thanks.

HarveyH42 · 9th September 2007, 04:16 PM

I don't know about 8051, but use AVR, mostly the Tiny series. Ordinary LEDs are 20-30 mA, and I've had no trouble running them directly from the MCU. I often omit the series resistor when I know the LED will be flashing, and never constantly on.

Check your data sheet. Most MCUs seem to be 20-25 mA per output, and around 200 mA total for the chip.

Leftyretro · 9th September 2007, 06:54 PM

You really need to download a data sheet for your specific 8051 MPU, it will specifiy the output high and low current ratings for all of the various output pins.

Lefty

**3v0** · 9th September 2007, 06:55 PM

Early uC like the 8051 could not directly source or sink a LED.

8051 microcontroller hardware interfacing tutorials circuits ...

In the above page

Quote:

The 8051 port pin can sink 1.6mA (3.2mA for port 0) and source 60uA.

Saying you have an 8051 is not very specific.

Sceadwian · 9th September 2007, 10:04 PM

8051's are seriously dated, unless you're required to learn them on a professional level you should learn to program AVR's are the newer PIC models. They're significantly more robust.

**Nigel Goodwin** · 9th September 2007, 10:20 PM

Quote:

Originally Posted by Sceadwian

8051's are seriously dated, unless you're required to learn them on a professional level you should learn to program AVR's are the newer PIC models. They're significantly more robust.

Well an AVR isn't a 'PIC model' at all, a PIC is a completely different device, which AVR attempted to steal market share from, even to the extent of using a three letter name!.

Either a PIC or an AVR would be a far better (and much more modern) solution, but presumably the OP is in India/Pakistan where they still seem to use the antique 8051's?.

Gayan Soyza · 10th September 2007, 11:17 AM

Quote:

Originally Posted by AceOfHearts

1) Is the 8051 current output always so low?

NO.To make it low you must clear the bit.

Quote:

Originally Posted by AceOfHearts

2) What is the best way to light up an LED connected to the 8051 to full brightness?

Use a 220R pull-up resister in series with the LED if the supply voltage is 5V.

simrantogether · 10th September 2007, 01:23 PM

Quote:

Originally Posted by AceOfHearts

I have noticed that my 8051 can barely light an LED. I tried connecting the LEDs ground directly without a current limiting resistor, yet it was very dim.

I am using the 8051 to drive other devices like LCD which works fine.

Is the 8051 current output really so low?

I did 'overheat' the 8051 once by accudentally connecting it in reverse polarity... But the device still works perfectly.

Its just lighting an LED. So....

1) Is the 8051 current output always so low?
2) What is the best way to light up an LED connected to the 8051 to full brightness?

Thanks.

well,

follow this site..

i think this link may help you..

This person is from Maharashtra..

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eblc1388 · 10th September 2007, 01:36 PM

Quote:

Originally Posted by Gayan Soyza

Use a 220R pull-up resister in series with the LED if the supply voltage is 5V.

What is the LED current in this case?

Does 8051 datasheet confirms 8051 port pin can allow this current?

mcs51mc · 10th September 2007, 01:55 PM

What part didn't you understand in the "Ports-Of-8051.doc" document?
http://www.electro-tech-online.com/m...-o-8051-a.html

Like Leftyretro aleady said, read the maximun sink & source current for you specific device

Sceadwian · 11th September 2007, 12:00 AM

That was supposed to read "AVR or newer PIC models". Older PIC's aren't much better than 8051's

Gayan Soyza · 11th September 2007, 05:16 AM

Quote:

Originally Posted by eblc1388

What is the LED current in this case?

9.54mA for 2.0V LED bulb.

Quote:

Does 8051 datasheet confirms 8051 port pin can allow this current?

Yes it is enough until 15mA.You are thinking about the source current but I'm telling about the sinking current.This old chip series good for sinking other than sourcing.

eblc1388 · 11th September 2007, 08:09 AM

Quote:

Originally Posted by Gayan Soyza

9.54mA for 2.0V LED bulb.

LED is a diode, not a bulb.
(5V - 2.0V)/220R = 13.6mA, not including saturation voltage of port pin.

Quote:

Originally Posted by Gayan Soyza

Yes it is enough until 15mA.You are thinking about the source current but I'm telling about the sinking current.This old chip series good for sinking other than sourcing.

I knew what I was thinking. So you think a 8051 port pin is good for sinking 15mA. You show seriously read the datasheet then.

Please give a reference to any document that shows 8051 can sink 15mA on its port pin.

**Nigel Goodwin** · 11th September 2007, 09:20 AM

Quote:

Originally Posted by Sceadwian

Older PIC's aren't much better than 8051's

??????

In what way?, and what 'older' PIC's?.

Gayan Soyza · 11th September 2007, 09:37 AM

Quote:

Originally Posted by eblc1388

(5V - 2.0V)/220R = 13.6mA, not including saturation voltage of port pin.

I reduced TTL output level 0.9V from the supply 5V.

5V-0.9V = 4.1V

4.1V-2V = 2.1V

2.1V/220R = 9.54mA

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9th September 2007, 03:32 PM	(permalink)
AceOfHearts	Microcontroller maximum current output... I have noticed that my 8051 can barely light an LED. I tried connecting the LEDs ground directly without a current limiting resistor, yet it was very dim. I am using the 8051 to drive other devices like LCD which works fine. Is the 8051 current output really so low? I did 'overheat' the 8051 once by accudentally connecting it in reverse polarity... But the device still works perfectly. Its just lighting an LED. So.... 1) Is the 8051 current output always so low? 2) What is the best way to light up an LED connected to the 8051 to full brightness? Thanks.

9th September 2007, 04:16 PM	(permalink)
HarveyH42	I don't know about 8051, but use AVR, mostly the Tiny series. Ordinary LEDs are 20-30 mA, and I've had no trouble running them directly from the MCU. I often omit the series resistor when I know the LED will be flashing, and never constantly on. Check your data sheet. Most MCUs seem to be 20-25 mA per output, and around 200 mA total for the chip.

9th September 2007, 06:54 PM	(permalink)
Leftyretro	You really need to download a data sheet for your specific 8051 MPU, it will specifiy the output high and low current ratings for all of the various output pins. Lefty

9th September 2007, 10:04 PM	(permalink)
Sceadwian	8051's are seriously dated, unless you're required to learn them on a professional level you should learn to program AVR's are the newer PIC models. They're significantly more robust. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

10th September 2007, 01:55 PM	(permalink)
mcs51mc	What part didn't you understand in the "Ports-Of-8051.doc" document? http://www.electro-tech-online.com/m...-o-8051-a.html Like Leftyretro aleady said, read the maximun sink & source current for you specific device

11th September 2007, 12:00 AM	(permalink)
Sceadwian	That was supposed to read "AVR or newer PIC models". Older PIC's aren't much better than 8051's __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."