Author Topic: Bad mojo  (Read 1037 times)

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Offline AethurTopic starter

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Bad mojo
« on: August 11, 2011, 09:12:40 PM »
I've got my board all together.. but I can't get it to power on correctly.

Powering through the voltage regulator the normal way yields no results, but if I touch the ground to the PD4 pin then my LED will come on.

Any ideas? PD4 should be grounded through the microcontroller correct?

Offline Soeren

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Re: Bad mojo
« Reply #1 on: August 12, 2011, 06:00:04 AM »
Hi,

How do you determine that it doesn't power on?

Don't connect parts, like the LED, that is connected to the controller, directly to power or ground. This may damage the controller or the output line.

Please post some sharp close-up photos of both sides of your board.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline AethurTopic starter

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Re: Bad mojo
« Reply #2 on: August 12, 2011, 06:58:18 AM »
Well, the LED isn't coming on, should it not?

I'll take some during lunch today! Thanks for the help

Offline waltr

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Re: Bad mojo
« Reply #3 on: August 12, 2011, 08:50:25 AM »
Quote
Well, the LED isn't coming on, should it not?
Only if the code in the processor sets the PD4 pin to the correct logic level.

What processor is this?
Did you load code into the processor?
Was it the correct code?
Does this code turn on the LED (set PD4 low)?

By any chance are you building the $50 Robot board? You didn't say that with your question so we will just take guesses at what might to wrong. If you are building the $50 Robot then there are many, many posts covering all of the common problems. Dig through this forum and read them.

The proper way to check for power is with a Voltmeter. Go buy one of the inexpensive DVMs to check the voltage out of the regulator.

Offline VegaObscura

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Re: Bad mojo
« Reply #4 on: August 13, 2011, 07:01:46 AM »
This is an issue that happens again and again.  Admin made a mistake when writing the LED part of the $50 bot tutorial.  Step 3B says:
Quote
Now add the LED as shown, slightly above the board. Make sure the longer lead (+) of the polarized LED is on the side closer to the DIP socket.
This is backwards from what it should be.  The shorter lead (the cathode) should be on the side closer to the DIP socket.  The idea here is that when the PD4 pin goes low, that means it is connected to GND.  Current then flows from the +5V power bus, through the resistor, through the LED, and finally into the pin on the ATMEGA.

You can fix this one of two ways.  You can either unsolder the LED, turn it around, and resolder it OR you can unsolder the side connected to the +5V power bus and connect it to GND instead.  Keep in mind that if you use the former method, the LED_on() and LED_off() functions will work as intended.  But if you use the latter method, they will do the opposite of what their name would imply.

Offline AethurTopic starter

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Re: Bad mojo
« Reply #5 on: August 13, 2011, 05:10:30 PM »
Thanks for the help here, I really just didn't know what I was doing..
I thought the LED would come on when the board was powered, I didn't realize it had to be programmed first!  Beginner mistake :)

 


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