Author Topic: $50 robot LED question  (Read 3319 times)

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Offline Metal Slug 2Topic starter

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$50 robot LED question
« on: December 17, 2008, 09:51:20 PM »
so i received my batteries today from all-battery.com (finally - it took forever because of the holiday season)

i plugged everything in and was testing everything with my multimeter.
everything seemed fine, a nice constant 5v etc. ........and then something bad happened
somehow the testing lead from my multimeter managed to complete a circuit with the LED, of course by battery was hooked up.  i saw the LED turn on, so i quickly took away the leads.
i am not sure if the LED is cooked or not - how can i test to see if it is?
if it is cooked, will i need to replace it?  :'( :'(


***EDIT***

I double checked why my LED had lit up, looked at the wiring and retested all connections.  I discovered that if you connect the two male header pins closest to the LED (and have your power supply plugged in) the LED will light up.  HOWEVER, do not be scared (as I was a moment ago), because this won't burn out your LED (err, at least i think so, based on my tests).  It seems when you connect the two pins, this connects the battery pack (or other power supply) with the LED and Resistor, basically completing a simple circuit.
This little trick may be useful for people to test whether or not their LED's are working or not...maybe?  Be cautious though: the LED is hooked up through the unregulated power (is that the right term?) if you do this.<-- (does this make any sense?)

If I have anything wrong here, or the LED shouldn't be lighting when i connect the pins, plz some1 let me know :)
« Last Edit: December 17, 2008, 10:28:01 PM by Metal Slug 2 »

Offline HDL_CinC_Dragon

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Re: $50 robot LED question
« Reply #1 on: December 17, 2008, 10:29:38 PM »
To check if its cooked just try to power it like you would normally
If it is in fact fried, then you will need to replace it unless you dont want your robot to have a status LED.
Chances are the complete circuit had the resistor in series so I think you should be ok. Depends on where in the circuit you made the short. If you had the $50 robot code loaded into the MCU already then chances are you didnt actually do anything. If im not mistaken, the LED comes on shortly after powering the MCU.
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Offline Metal Slug 2Topic starter

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Re: $50 robot LED question
« Reply #2 on: December 17, 2008, 10:33:29 PM »
To check if its cooked just try to power it like you would normally
If it is in fact fried, then you will need to replace it unless you dont want your robot to have a status LED.
Chances are the complete circuit had the resistor in series so I think you should be ok. Depends on where in the circuit you made the short. If you had the $50 robot code loaded into the MCU already then chances are you didnt actually do anything. If im not mistaken, the LED comes on shortly after powering the MCU.
Thanks,  ;D I haven't installed the MCU yet.  I figured out the problem, which actually isnt much of a problem, but thx for the help n e ways .

Offline HDL_CinC_Dragon

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Re: $50 robot LED question
« Reply #3 on: December 17, 2008, 10:38:17 PM »
no problem. If im not mistaken, you might have your LED in backwards? Voltage is supposed to flow from pin 7 through the LED and sink into pin 6. Since LEDs are polarized, they will only light when voltage goes in the right direction. When you shorted the two pins, voltage was flowing in the opposite direction from the unregulated input rail and back into pin 7. May want to double check on that one
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Offline pomprocker

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Re: $50 robot LED question
« Reply #4 on: December 18, 2008, 12:29:34 AM »
Here is a good read

http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=57

You want to look down by the LED paragraph

Offline ed1380

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Re: $50 robot LED question
« Reply #5 on: December 18, 2008, 07:24:48 AM »
im guessing you shorted one of the pins from the power bus to pin 6 on the mcu (pin 5 on the servo bus)
thre is a resistor on there, and even if there wasnt, the split second isnt enough to burn the led
Problems making the $50 robot circuit board?
click here. http://www.societyofrobots.com/robotforum/index.php?topic=3292.msg25198#msg25198

Offline Metal Slug 2Topic starter

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Re: $50 robot LED question
« Reply #6 on: December 18, 2008, 03:16:39 PM »
no problem. If im not mistaken, you might have your LED in backwards? Voltage is supposed to flow from pin 7 through the LED and sink into pin 6. Since LEDs are polarized, they will only light when voltage goes in the right direction. When you shorted the two pins, voltage was flowing in the opposite direction from the unregulated input rail and back into pin 7. May want to double check on that one

hmmm  :(  i've quintuple checked that the LED was put in the correct way, and it is.
when your talking about pins, are you reffering to the pins of the MCU?

Offline HDL_CinC_Dragon

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Re: $50 robot LED question
« Reply #7 on: December 18, 2008, 03:55:48 PM »
I was referring to the pins in the headers... perhaps I didnt read your original post correctly and im thinking of the wrong pins that you accidentally shorted. In which case: Sorry >_<

Was it the header pins you were contacting or the MCU pins?
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Offline Webbot

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Re: $50 robot LED question
« Reply #8 on: December 19, 2008, 02:34:52 PM »
Dont forget that the $50 design means that the LED is NOT a power indicator. By default it will NOT light up unless you write some code to make it do so.
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Offline Metal Slug 2Topic starter

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Re: $50 robot LED question
« Reply #9 on: December 20, 2008, 02:38:24 PM »
I was referring to the pins in the headers... perhaps I didn't read your original post correctly and I'm thinking of the wrong pins that you accidentally shorted. In which case: Sorry >_<

Was it the header pins you were contacting or the MCU pins?

i was referring to the header pins which are meant for the servos to plug into, not the MCU pins.

Offline HDL_CinC_Dragon

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Re: $50 robot LED question
« Reply #10 on: December 20, 2008, 03:39:34 PM »
hmmm I looked at the way the board should be wired again and if you shorted the middle pin with the pin nearest the MCU socket unregulated voltage should be flowing from the battery pack, through the resistor, through the LED, into pin 7, across pin 21, up the center pin line on the other sides headers and push into the vregs regulated output... I hope I didnt over look something and am wasting your time lol
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Offline Razor Concepts

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Re: $50 robot LED question
« Reply #11 on: December 20, 2008, 06:14:23 PM »
If it helps, the LED specified in the $50 robot can be backwards - the shorter leg being positive, and the longer being negative. Seems like an error in manufacturing.

Offline Admin

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Re: $50 robot LED question
« Reply #12 on: December 28, 2008, 01:44:39 AM »
If it helps, the LED specified in the $50 robot can be backwards - the shorter leg being positive, and the longer being negative. Seems like an error in manufacturing.
uhhhhh I don't think a manufacturer would make that mistake . . . more likely its just a bad LED . . . you can find tons in old electronics and probably radioshack for cheap

Offline Metal Slug 2Topic starter

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Re: $50 robot LED question (solved)
« Reply #13 on: February 12, 2009, 10:27:44 PM »
 >:( :P....well i found the problem....I decided today i would test the LED to see which way the anode and cathode were facing relative to the MCU.  you guys were all right...i had installed the LED backwards. --_--  i found the origin of my mistake.  I had soldered the LED in place based on the picture shown in the $50 robot tutorial.  Apparently this was backwards for me.  The picture is the first one with the LED soldered on the board. http://www.societyofrobots.com/step_by_step_robot_step3B.shtml

Thanks for the help anyways!  :)

Offline Borot

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Re: $50 robot LED question
« Reply #14 on: January 23, 2010, 08:29:03 AM »
cheers,
I was wondering why my LED wasn't lit, it doesn't until programmed to do so!

Offline Mansoor

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Re: $50 robot LED question
« Reply #15 on: July 22, 2010, 09:38:21 AM »
I am gonna call Admin out on this one  ;D

The LED in the pic is wired in the opposite direction. I kept looking at the pic then reading what you wrote and they are opposites. you told us to solder the LED with + toward DIP socket. you did it the other way around. In the header you define LED_on as pin 6 off. which makes sense cause then the current will sink into pin 6. LED_off is the opposite. so both these commands are ready to go LED_on turns on the LED and LED_off turns it off. yet in the code you have LED_off to turn ON the LED. I am confused how can the LED turn on if it is wired incorrectly? that should be impossible since the led is polarized.

okay let me say thanks to admin for sharing his experience in robotics with everyone. I am not trying to say that i know anymore in robotics than a 5 year old. It just feels good when I catch something the pros missed  :).
« Last Edit: July 22, 2010, 11:22:13 AM by Mansoor »

Offline Admin

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Re: $50 robot LED question
« Reply #16 on: July 22, 2010, 11:33:20 AM »
I did this many years ago (5?) so I don't really remember what happened but . . .

I think the code was just accidentally inverted, or even maybe just a commented section contained wrong information. A dumb typo, but everything still worked so I didn't catch it.

There are two different ways to control an LED with a mcu. By having the short end plugged into the socket, bringing the pin low turns the LED on. By having the long end connected to the socket, bringing the pin high turns on the LED.

 


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