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Topic: Atmega 328 and TLC5940 routing (Read 6 times) previous topic - next topic

AJB2K3


Quote
and added the bypass to the tlc5940


The processor also needs them.



Where? i haven't seen one any ware?
Sorry for the noobish post but my knowledge is 10 years out of date!

Coding Badly


http://www.atmel.com/images/doc2521.pdf

Page 2: 2.1 Digital supply section.

Page 14: Figure 6-1...
Quote
Decoupling on all VCC/GND pairs


Put a 0.1uF capacitor across all (A)VCC / GND pairs as close as possible to the processor.

AJB2K3

#17
Apr 01, 2013, 07:51 pm Last Edit: Apr 01, 2013, 07:54 pm by AJB2K3 Reason: 1
?? not on here?

http://arduino.cc/en/Main/Standalone

Stupid additional question but I plan on running this of a 3.6v PSP battery (always have 2 spare in camera bag + 1 in each of my psp1001 consoles)

Am I supposed to change some component values?

Stupid question and you have permission to roll your eyes.
Sorry for the noobish post but my knowledge is 10 years out of date!

AlxDroidDev


?? not on here?

http://arduino.cc/en/Main/Standalone


The bypass caps are there (2 x 10uF caps): one is in the output of the 7805 voltage regulator. In all the pictures where the breadboard appears with the 7805, the bypass cap for the Atmega328 is the upper rightmost cap. Note that the 7805 also requires an input capacitor and it is also there, to the left of the other capacitor, also 10uF.

Learn to live: Live to learn.
Showing off my work: http://arduino.cc/forum/index.php/topic,126197.0.html

Coding Badly

?? not on here?


Unfortunately, it is a common mistake to exclude them.

With those two digital chips on your board there is a high probability you will have problems without the bypass capacitors. If you do not include them and have problems you will be pulling your hair out trying to figure out what is wrong.

Coding Badly

The bypass caps are there (2 x 10uF caps): one is in the output of the 7805 voltage regulator.


Those capacitors serve a different purpose than the VCC/GND capacitors.  Both are important.  The 0.1uF capacitors across VCC/GND are not present in that circuit but should be.


Coding Badly

Stupid additional question but I plan on running this of a 3.6v PSP battery (always have 2 spare in camera bag + 1 in each of my psp1001 consoles)


The voltage is in range for the TLC5940.

The voltage is slightly out of range for the AVR processor at 16 MHz.  Many many people run the processor slightly out of the voltage range.  I have never read about any problems.  You will have to use your own judgement.  Obviously, if you were building a pacemaker, you should choose a different path.  If you were building a light display, running the processor a bit out of specifications is not a problem.

AlxDroidDev


The bypass caps are there (2 x 10uF caps): one is in the output of the 7805 voltage regulator.


Those capacitors serve a different purpose than the VCC/GND capacitors.  Both are important.  The 0.1uF capacitors across VCC/GND are not present in that circuit but should be.


You are correct.

After I read your answer I wrote some gibberish here and then I deleted it after I studied some more.

Although the cap I mentioned helps a bit, each and every chip should have its own decoupling (aka "bypass") capacitor, to prevent it from suffering voltage drops caused by the rest of the circuit. I am glad I have always done that in my designs.
Learn to live: Live to learn.
Showing off my work: http://arduino.cc/forum/index.php/topic,126197.0.html

AJB2K3

My pcb is a varient of the trihole pad design but has two tracks made to run under the chips as supply lines. Would it be ok to put it across these lines at one end of the chips? or should I hide them under the ic sockets as close as possible to the chips power pins.
Sorry for the noobish post but my knowledge is 10 years out of date!

Coding Badly


I can't help with that one.  If you don't get an answer in a few days, let me know (personal message) and I'll use my moderater-fu to try and get you an answer.

AJB2K3

Even more confused. now with bypass caps.

In one diagram I see them placed between the + supply and the VCC pins, and another diagram put across the + & - supply lines.
Which one is correct?
Sorry for the noobish post but my knowledge is 10 years out of date!

Coding Badly

In one diagram I see them placed between the + supply and the VCC pins


Wrong.

Quote
and another diagram put across the + & - supply lines.


Correct.

The capacitor is connected from (A)VCC to GND as close as possible to the chip.

AJB2K3


In one diagram I see them placed between the + supply and the VCC pins


Wrong.

Quote
and another diagram put across the + & - supply lines.


Correct.

The capacitor is connected from (A)VCC to GND as close as possible to the chip.



Thats what I thought, thanks.
Sorry for the noobish post but my knowledge is 10 years out of date!

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