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Best way to power a LED (Pinguino vs Arduino) ?
16-05-2016, 03:29 PM,
#1
Best way to power a LED (Pinguino vs Arduino) ?
It was pointed out to me the other day that the pinguino user LED is power sourced from VCC (anode goes to VCC) and ground goes to the resistor then the pinguino pin. (Send LOW to turn it on and HIGH to turn it off.)

This is opposite from the 'user' pin on an arduino which has the anode to the pin and cathode to resistor to ground.

Actually in every diagram I remember seeing, long before the arduino ever was, an LED was powered from the PIC PIN (anode connected to PIC PIN) and cathode to resistor to ground.

Programmatically the thinking is that sending HIGH turns things on (and LOW is off) so, originally, was the design of the electronics done to match the program thinking?

I think the best way electronically is to source the LED from the best source of power which is direct to VCC? correct?

Anyone know the history or reasoning on this?

And should we be consistent when we wire other LEDs on the pinguino to match the wiring of the user LED so the programming is the same?

This has me curious..

earl
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16-05-2016, 04:17 PM, (This post was last modified: 16-05-2016, 04:23 PM by gtcbreizh.)
#2
RE: Best way to power a LED (Pinguino vs Arduino) ?
You misinterpreted my explanation.
The cathode is connected to a 470 Ohm resistor, connected itself to the #29 pin (RA4 for the 18f4550 chip). There is no connection to the true Ground. This is your application which set the pin to 0 Volt to light on the led (or 5V to light off).
Take a look at http://wiki.pinguino.cc/index.php/PIC18F4550_Pinguino.
For me the 2 methods are electrically equivalent. In any case you cannot tell the Arduino's is better.

N.B. We find, relating to the leds, the same schematics on the Olimex PIC32 pinguino micro.

André
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16-05-2016, 07:51 PM,
#3
RE: Best way to power a LED (Pinguino vs Arduino) ?
(16-05-2016, 03:29 PM)earlct Wrote: Actually in every diagram I remember seeing, long before the arduino ever was, an LED was powered from the PIC PIN  (anode connected to PIC PIN) and cathode to resistor to ground.
Really? I think it is quite usual to drive things "low-active".
For example have a look at the RX/TX LEDs at some VCP devices like the FT232 or the MCP2200.

This "low-active" signalling may have historical reasons because the NPN or N-Channel Fet transistors have been better than the PNP and the P-Channel ones.

There are other advantages like you can switch things connected to higher voltages more easy using Open-Collector or Open-Drain Pins.

It may be not common to Arduino users, because it is to complicated for them to think low-active ;-)
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