$50 Dollar Robot Blinking LED

[ekcnepta]

Hey everyone,

I am a Computer Science student just getting into robotics and electronics. I built the $50 robot and made the LED turn on every time the power is on. For about a month everything has been working fine until recently, when I noticed that when I turn the power on, the LED would start blinking very fast. My LED burned out shortly after I noticed it was blinking. I just replaced it, and I am sure that I connected the replacement the right way, but it blinks as well. I noticed it would only blink when one or both servos are connected to the circuit and stays constantly lit otherwize. Connected or not, the photoresistors do not seem to affect it.

I wanted to ask you, is there a chance any of the components have burned out and do you think I should worry about that? I am attaching an IR distance scanner next week and would like to make sure everything works properly. Unfortunately, I do not have any equipment to measure the voltage in the circuit. I am using a 6V pack to power both the servos and the microcontroller ATMega8.

I would appreciate your feedback! Thanks for the great website!

[Miles]

maybe check the battery is fully charged

[ekcnepta]

Thanks for the response!

I just replaced the batteries with new ones. Unfortunately, the LED keeps blinking when I connect the servos.

[Miles]

Are you using the circuit board in the tutorial? Also does the robot still do it's job driving around and reacting to light?

[ekcnepta]

Yes, I am using the circuit board from the tutorial, and the robot does react to light. It works perfectly fine except for the light changing it's brightness all the time.

[jamort]

one possibility.. is there a resistor before the led i know this can make them short another possibility is a loose connection

[ekcnepta]

Well, the only resistor connected to the led is the 1.62Kohm resistor between GND and pin 6. Could you explain what you mean by a loose connection? I checked the leads, and all of them are soldered where they should be. It is possible I made a cold connection while soldering though. Is it possible that that would cause the change in brightness? Thanks!

[jamort]

that is actually every possible i know when i first took electronics the first thing we had to do was solder leds in a simple circuit and just about all of ours were blinking because of a loose connection... occaisionally i have seen a faulty led that will cause this too but were this is you second one i doubt that is it... if you have a bread board try building the circuit on that and see if you still have the problem and if you do mess around with it and see if you can stop it...
are you sure the other led went out... the connection could of simply came loose...

[ekcnepta]

Thanks for the feedback, jamort! It turned out the other led had not burned out. I can not explain why it had stopped working earlier.. I resoldered the second led and it still keeps blinking when I connect the servos. Unfortunately, I don't have a breadboard to reconstruct the circuit. It sounds like the problem isn't a burned out component, so I am happy about that. Would you say it is safe to continue using the circuit board like that? Can I safely add the IR sensor?

[jamort]

I think its safe.. I wonder if maybe the servos are for some reason drawing a lot of current causin the led to blink were it works with out the servos?... but were you put the "blew" led back on it and it worked again its probably a soldering problem but dont worry it can be hard to solder your first time...
Go ahead add the ir sensor... the worst thing that can happen is a little fire... lol but i doubt that...

[ekcnepta]

Lol! Thanks for the feedback. I will add it on monday and hope nothing burns down.

[jamort]

ok... and feel free to put some pics up... even if it is the $5o robot... though i havent got any up yet cause i dnt have a camera... rather waste my money in components and sensors

[Miles]

are you using the resistor values suggested in the tutorial? If you are then the resistor that controlls current to the LED should be about 340ohms not the 1.62k.  Also just check if you have connected the LED and resister properly in terms of the whole circuit.

[ekcnepta]

Hey guys,

Once again, thanks a lot for your help. I am certain I am using the resistor from the tutorial and that I have connected the components properly. Sorry for the mixup.. It must be the 340ohms resistor if that is the one used in the tutorial, as they look exactly the same.
I will install the IR sensor tomorrow and let you know how everything goes.. If everything goes well, I will def post some pictures afterwards!