Pages: [1] 2   Go Down
Author Topic: Big capacitor near microcontroller - Circuit stops working  (Read 3085 times)
0 Members and 1 Guest are viewing this topic.
Brasília, Brazil
Offline Offline
Jr. Member
**
Karma: 0
Posts: 54
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hello guys,

I have a circuit and when I put a big capacitor (330uF) near the atmega, the atmega gets stuck after running for a while. When I discharge the capacitor the circuit works again for a while and then stops again. On oscylloscope, i saw that the circuit stops working after the capacitor charges.

If I take that capacitor out, the circuit works perfectly.

I have an atmega168 running at 8mhz, with external crystal, and in the board there are also shift-registers and uln2803 drivers to control a LED matrix.

Does anyone knows what's happening? The circuit is working, as I took the capacitor out, but I'd like to know what happened so i don't make the same mistake in future projects.

Thanks for any help...
Logged

Global Moderator
Boston area, metrowest
Online Online
Brattain Member
*****
Karma: 548
Posts: 27372
Author of "Arduino for Teens". Available for Design & Build services. Now with Unlimited Eagle board sizes!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

What is the big cap connected to? From your parts listed, I can't see any reason for it to be across anything but power & ground.
Logged

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Brasília, Brazil
Offline Offline
Jr. Member
**
Karma: 0
Posts: 54
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Exactly, it`s connected between power and ground... I forgot to mention, the capacitor is eletrolytic
Logged

Global Moderator
Boston area, metrowest
Online Online
Brattain Member
*****
Karma: 548
Posts: 27372
Author of "Arduino for Teens". Available for Design & Build services. Now with Unlimited Eagle board sizes!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Electrolytic, so  it's polarized? Not installed backwards?
Got a schematic we can look at?
Logged

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Brasília, Brazil
Offline Offline
Jr. Member
**
Karma: 0
Posts: 54
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Already checked that... it's on the right direction...
Logged

Global Moderator
Boston area, metrowest
Online Online
Brattain Member
*****
Karma: 548
Posts: 27372
Author of "Arduino for Teens". Available for Design & Build services. Now with Unlimited Eagle board sizes!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

So, back to reply #3: Got a schematic we can look at?
Logged

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Brasília, Brazil
Offline Offline
Jr. Member
**
Karma: 0
Posts: 54
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Here's the schematic...

DATA_ROW, DATA_COL, etc, etc, goes to the shift registers... The board supports a rf, but it's not installed, so it's not the problem...

Actually, I don't even know why I put that capacitor there, but now i'd like to know what's happening

and hey... thanks for the reply... I wish we can solve that


* schm.jpg (122.96 KB, 711x494 - viewed 50 times.)
Logged

SF Bay Area (USA)
Offline Offline
Tesla Member
***
Karma: 137
Posts: 6792
Strongly opinionated, but not official!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
On oscylloscope, i saw that the circuit stops working after the capacitor charges.
a 300uF cap directly across the power rails should charge pretty much instantly, right?

It almost sounds like you have the cap in between the AVR and one of the power rails.  Except I calculate the time would still be very short...
Logged

Brasília, Brazil
Offline Offline
Jr. Member
**
Karma: 0
Posts: 54
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

At AREF, it's just decoupling capacitor as in the datasheet... Anyway, I am not using the AD...

Maybe it's not the charging that makes it stop... I thought that was the reason, cause when I saw it discharged, the circuit worked again... it doesn't work too long by the way
« Last Edit: March 18, 2011, 12:46:47 am by brenin » Logged

Global Moderator
Dallas
Offline Offline
Shannon Member
*****
Karma: 210
Posts: 13039
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
At AREF...
Sorry I didn't get my post removed in time.  Please pretend you never saw it.   smiley-red
Logged

Global Moderator
Boston area, metrowest
Online Online
Brattain Member
*****
Karma: 548
Posts: 27372
Author of "Arduino for Teens". Available for Design & Build services. Now with Unlimited Eagle board sizes!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Surface mount part eh?

Are you sure the cap is connected to where you think it is?  What does the cap charge up to when it stops working?
Once VCC is over ~3.9 volts, the processor should just run, and if it continues to  5V it should not make a difference.

If the power supply has enough current, the cap should charge up almost immediately if it is actually connected to VCC.
Logged

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Brasília, Brazil
Offline Offline
Jr. Member
**
Karma: 0
Posts: 54
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

It charges pretty fast...

the atmega, the 100n caps and the shift registers are smd... the capacitor itself is pth

I'm starting to think that the behavior after I discharge the capacitor is just a coincidence, and it's charging is not actually the reason of the problem...
Logged

Offline Offline
Edison Member
*
Karma: 3
Posts: 1001
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

There appears to be a number of issues with your schematic/wiring. For starters I notice the following:


- AREF should be pin 21
- Avcc should be pin 20
- Gnd should be 8 and 22
....

You better check them all and match the corrected schematic to your wiring.
Logged

Global Moderator
Boston area, metrowest
Online Online
Brattain Member
*****
Karma: 548
Posts: 27372
Author of "Arduino for Teens". Available for Design & Build services. Now with Unlimited Eagle board sizes!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

The pinouts are correct for a 32-pin quad flat pack part.
Logged

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Brasília, Brazil
Offline Offline
Jr. Member
**
Karma: 0
Posts: 54
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

CrossRoads is right... it smd part, so the pins are a bit different from the regular dip part...
Logged

Pages: [1] 2   Go Up
Jump to: