GPO in LK204-25PC...some smoke here....

[ulisses]

Hello,

I have a LK204-25PC.
I was programming and testing it, everything was working fine, buttoms, etc, until I tried to test 3 LED's in the GPO's connections.
The Led's are 12V and I connected LED 1 to GPO 1-2, LED 2 to GPO 3-4. LED 3 to GPO 5-6.
I used the iotest software to test the GPO, and when I tried to test GPO2, the light turned on, came brighter, brighter, until some smoke started in the unit. I immediately disconnected the power supply cable and GPO cables....the GPO2 circuit is melted (I think, not sure), but the LCD and functions buttoms are working fine. I think my GPO2 gone, how I test ?

What I did wrong ? I though the led's cable inverted shouldn't be a problem.

Thanks a lot,
Ulisses Simionato

[Henry]

did you have current limiting resistors in place?

[ulisses]

no....just a direct connection to the led....

led pin 1 to GPO1
led pin 2 to GPO2

thanks,
Ulisses

[Henry]

the GPOs on the LK204-25-PC have no current limiting resistors, you have to add them if you want to use LEDs...

Remember

V=IR Voltage = Current * Resistance

The GPO has 12V and the LED has 0 resistance (it has some, but very very little)

12V = I * 0

This equals infinite current through the GPO, thus blowing the MOSFET up (I tested the GPO to 1.1Amps and it still worked). I am suprised that the GPO blew up, I would have expected the LED to blow up instead.

[ulisses]

Both blew up, led and GPO2, I just tested GPO1 and GPO3 with new leds (different brand) and it's working fine (without resistors)
maybe the first leds were 5 volts, not 12....not sure right now.

Anyway I lost GPO2...

I'm copying this project:
http://www.digital-flight.com/lcd_project.htm

Thanks for all the help !
Ulisses

[linear]

okay, a few observations:

LEDs aren't inherently 12V devices--there are some packaged for automotive applications that include a resistor designed to let them operate on 12V, is this what you have?

Second, you would normally connect an LED across one GPO, not two. Each row of GPO pins is one output, put your LED across those.

o o GPO1
o o GPO2
o o GPO3
o o GPO4
o o etc.
o o
o o
o o

[Henry]

That is a very nice project! I have seen it a few weeks back and posted about it in the General Section. I might be able to send you a new MOSFET if you feel like giving it a shot at soldering.

As well, some times you will not be able to blow the LED if the power supply cannot handle giving out the infinite current and is limited to something like 1amp...

[ulisses]

Maybe the led I tested now has a resistor inside, is there a way to check that testing the led ???
Hnery, how do we manage the MOSFET replacement ?

Thanks,
Ulisses

[Henry]

e-mai lme, henryj@matrixorbital.com with all your shipping info and we will send something out.

[ulisses]

Henry,

I tried 3 times to send you an e-mail with my address but it returned as undelivered.
Do you have another e-mail ?

Anyway, here is my address for the replacement:

ALPHALINE TRADING CORPORATION
Att. Ulisses Simionato

2898 NW 79 Avenue
Miami FL - 33122-1033
Ph 305-471-0020 - Fx 305-471-7980

Thanks a lot,
Ulisses Simionato
uli1@uol.com.br

[Cheese]

Second, you would normally connect an LED across one GPO, not two. Each row of GPO pins is one output, put your LED across those.

o o GPO1
o o GPO2
o o GPO3
o o GPO4
o o etc.
o o
o o
o o

That's exactly what I thought when I just read this, are you sure you're connecting the LED's to the correct pins?

you shouldn't ever have any connections between GPO 1 and 2.

Rob.

[ulisses]

it's correct and solved now...

I installed 12V lamps (probably with resistor inside) and it's working fine...I guess led's need resisitors as said here.

The only problem is that I lost GPO2, the small black box to the left of the GPO2 pins burned.

Thanks,
Ulisses