$50 robot LED broken?

[pomprocker]

When is the LED suppose to light up?

I have not seen my LED light up yet, and I am using the 9volt and the 4.8 volt pack on my $50 robot.

[Admin]

It should light up as soon as your board is programmed.

(the LED is software controlled)

ps - I just deleted your double post - only post a problem once!

[pomprocker]

Yes it is programmed and everything works fine except for the LED not lighting up.

I suppose I could get more from Radio Shack and connected them directly to power and ground like you said.

[ed1380]

admin correct me if I'm wrong. (hopefully I'm not)

change

Code: [Select]

LED_off();//turn LED on
toward the top of the code to

Code: [Select]

PORT_OFF(PORTD, 4);it'll make the led always stay on as long as the mcu is on. I've had problems with it sometimes not flashing at startup too. seems random

[Admin]

Or . . .

you change it to

Code: [Select]

LED_on();

[pomprocker]

This is what I see:

Code: [Select]

void LED_on(void)
{
PORT_OFF(PORTD, 4);//turn LED on
}
void LED_off(void)
{
PORT_ON(PORTD, 4);//turn LED off
}

[ed1380]

that's in the header file where admin defines the LED_on and LED_off functions.

the red box is where it's at. in the photovore_v1.c file


O NOES. did admin make a mistake? (blue boxes)

[pomprocker]

how does LED_off turn it on             

[ed1380]

the negative side of the led is connected to the MCU. so you have to set teh port low for it to turn on.

[pomprocker]

what?


pardon my density

[Trumpkin]

you have to program the port low for the LED to turn on.

[HDL_CinC_Dragon]

Ok whats happening is that the Micro controller(MCU) is constantly trying to apply power to the pin that the LED is hooked up to but the other end of that connection is hooked up to VCC so basically the two forces cancel each other out and the electricity doesnt flow. When you want to turn the LED on, you set the port low(hence the PORT_OFF) so that way theres nothing stopping the electricity from flowing into the MCU from the VCC line and thus the LED gets power. The MCU is NOT powering the LED but rather the VReg is directly powering the LED(Through a resistor also! This is a very very important detail!!) and the MCU is serving as ground for the power to go to.

Hope this helped

[Admin]

O NOES. did admin make a mistake? (blue boxes)

The blue boxes are correct . . . yea I know, its not intuitive, but its correct.

As for the red box, I had made a change in the code without changing the comment . . . you aren't the first to mention this mistake in the forum

[pomprocker]

So, I changed it to LED_on; and did another build and wrote it to the atmega8.

The LED still doesn't come on.

How would I go about testing it with a multimeter? What should I be looking for?

[ed1380]

set the mm to measure voltage. put the positive probe on the positive power bus. (should be teh middle row in the sensor pins)
and put the negative probe on the pin the led is connected to.
when you turn the atmega8 on the mm should read about 5v. if it does then the led might be bad.

[Webbot]

Make sure the LED is connected the right way round. Being a diode it will only work if connected the correct way. Check out the LED guides http://www.societyofrobots.com/electronics_led_tutorial.shtml

[DC-Electronics]

Might as well toss my 2 cents in. Did you heat sync each leg before soldering it on?
Could be you burnt your LED out. If so..... Il sell you a new one...  lol

[HDL_CinC_Dragon]

good way to test your LED is to get a AA battery, tape a little wire onto each side, and touch the contacts accordingly with polarity. If it lights up, youre good to go. if it doesnt even when you touch the contacts to both sides (switching the leads that you touch with the wires), you have a bad LED. Make sure you test the AA battery too. It should be giving about 1.5 volts. Set your DMM to the 2v range and test for voltage.
Hope this helped

[pomprocker]

Yes, I used heat sinks.

I actually read somewhere that you should not use heat sinks because it makes it take long to heat up the component.

With a 30w pencil at about 645deg is should only take like 5 seconds or less.

I remember I was counting to 10 before the solder would start flowing onto the component.

I later learned this trick where you should melt a little solder between the pencil and the component as it increases heat transfer.

[HDL_CinC_Dragon]

I later learned this trick where you should melt a little solder between the pencil and the component as it increases heat transfer.

Yep, thats whats meant by "tinning the tip". I accidentally messed the tip up on my soldering iron so it oxidizes within a couple seconds, but instead of buying a new one, I just touch the tip to the joint I want soldered, touch the solder to the tip and the lead at the same time, and right when the solder melts I move the solder to the opposite end of the joint as the soldering iron so that I get a good complete joint. Works perfectly every time.