Arduino Forum

Topics => Product Design => Topic started by: cjdelphi on Oct 08, 2013, 01:51 pm

Title: SMT LEDs next to every pin.
Post by: cjdelphi on Oct 08, 2013, 01:51 pm
to signal a high or low signal, they could transistor driven or taken from the pin and a 1k resistor?
Title: Re: SMT LEDs next to every pin.
Post by: CrossRoads on Oct 08, 2013, 06:35 pm
You would have them turn on when the header pin was high, either from an output pin, or from an external source? I would think you'd want a small pulldown also to keep a floating input from turning on the LED.
Title: Re: SMT LEDs next to every pin.
Post by: tronixstuff on Oct 09, 2013, 01:08 pm

to signal a high or low signal, they could transistor driven or taken from the pin and a 1k resistor?


Something like this?
http://tronixstuff.com/2013/04/18/review-lbe-magpie-arduino-compatible-board/
Title: Re: SMT LEDs next to every pin.
Post by: cjdelphi on Oct 09, 2013, 01:30 pm
lol yup, exactly like that :)
Title: Re: SMT LEDs next to every pin.
Post by: tronixstuff on Oct 09, 2013, 01:33 pm

lol yup, exactly like that :)


design files - https://github.com/schappim/magpie
Title: Re: SMT LEDs next to every pin.
Post by: cjdelphi on Oct 09, 2013, 01:45 pm
You know what....

I've never designed a PCB in my life (except for surface mounted soldering onto perfboard using just flux and a soldering iron and sometimes maybe the heatgun if i mess up), eg no CAD experience (yet)

But, surface mounted NPN transistors give roughly up to 500ma of current right? (off the top of my head the 2222 smt)  if you used a transistor on each pin to not light an LED, but to simply protect the atmega chip from drawing too much current (a 1k resistor from each pin)

*The transistor will protect the arduino pin from damage.
*Allow much greater current to be drawn from the USB.

(or with a protection diode)

*Drive relays directly from the Pin.

Anyway I'll be keeping an eye on the Magpie...  I have a growing collection of Aussie boards now :)
Title: Re: SMT LEDs next to every pin.
Post by: CrossRoads on Oct 09, 2013, 04:53 pm
You'd  need 2 transistors - one to sink current, one to source current, and then some way to turn them both off so the atmega pin could be an input also.
Take a look at the ruggedcircuits card - series resistor in the form of a resettable fuse-type part and with a zener to protect against overvoltage coming in.
I designed a Mega shield to add protection between screw terminals and header pins, added so many parts that the price was not supportable.
Title: Re: SMT LEDs next to every pin.
Post by: cjdelphi on Oct 09, 2013, 05:29 pm
Hmm yes forgot about sinking current... shame
Title: Re: SMT LEDs next to every pin.
Post by: CrossRoads on Oct 09, 2013, 06:23 pm
Add a little DIP switch with each pin, manually flip them to enable the drive transistors.
Or add a shift register that you write to enable the drive transistors.