Pages: [1]   Go Down
Author Topic: Standalone arduino/capacitors  (Read 873 times)
0 Members and 1 Guest are viewing this topic.
Finland
Offline Offline
Sr. Member
****
Karma: 1
Posts: 270
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I'm building my first standalone arduino project (atmega328 on stripboard). I power it through a 7805 regulator which has 10uF caps on input and output. The 7805 is on a separate circuit board. The wire from the 7805 to atmega328's VCC is about 20 cm (ten inches) long, quite thick (0.75mm2) wire, plus about ten cm on the stripboard.

Should I place an additional cap between atmega328's VCC and GND (and AVCC and GND) close to the pins? And what would be a proper size for the cap?
Logged

Manchester (England England)
Offline Offline
Brattain Member
*****
Karma: 597
Posts: 33292
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
Should I place an additional cap between atmega328's VCC and GND (and AVCC and GND)
Yes.
0.1uF
Logged

Finland
Offline Offline
Sr. Member
****
Karma: 1
Posts: 270
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

OK, thanks Mike. Does it have to be elco or will ceramic do?
Logged

Left Coast, CA (USA)
Offline Offline
Brattain Member
*****
Karma: 361
Posts: 17259
Measurement changes behavior
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

OK, thanks Mike. Does it have to be elco or will ceramic do?

Actually ceramics are preferred.

Logged

0
Offline Offline
Shannon Member
****
Karma: 199
Posts: 11650
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

It wouldn't matter where the regulator and its electrolytics were, that 0.1uF cap is required always, right next to the chip.  Decoupling capacitors should have low ESR and ESL, which in practice means ceramic, right next to the relevant pins.  The exact value isn't too important,
BTW, so anything from 0.1uF to 1uF will work fine.
Logged

[ I won't respond to messages, use the forum please ]

Canada
Offline Offline
Sr. Member
****
Karma: 0
Posts: 318
Sometimes teaching, always learning,
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I have a strip of 0805 0.1uF caps on hand. They can be soldered between the VCC/GND and AREF/GND pins on the bottom of the 328 chip. Quite handy and not at all hard to do.
Logged


Valencia, Spain
Offline Offline
Faraday Member
**
Karma: 142
Posts: 5290
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

BTW, so anything from 0.1uF to 1uF will work fine.

1uF ceramics are quite big... smiley

Logged

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

Finland
Offline Offline
Sr. Member
****
Karma: 1
Posts: 270
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Thank you all for thorough explanations. I'll use 0.1 uF ceramics then.
Logged

SF Bay Area (USA)
Online Online
Tesla Member
***
Karma: 124
Posts: 6634
Strongly opinionated, but not official!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
1uF ceramics are quite big
Not anymore.  You can get 10uF in 0805...
Logged

Canada
Offline Offline
Sr. Member
****
Karma: 0
Posts: 318
Sometimes teaching, always learning,
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

0805 is so yesterday.

Here's a 10uF cap in 0402:
http://www.digikey.ca/product-detail/en/C1005X5R0J106M/445-8920-1-ND/3507812
« Last Edit: December 11, 2012, 08:55:23 pm by John_S » Logged


Pages: [1]   Go Up
Jump to: