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Topic: Questions on making a minimal/custom Arduino circuit @ 3.3v/8Mhz? (Read 3 times) previous topic - next topic

xl97

Hi Robert-


outside of some I/O pins for some basic smd leds......and some buttons input to make those leds do something..... I dont think any (but I'll have to review to be sure)  :)

your schematic looks similar to mine  (I'll post when I get to work)..

but mine is missing the cap on the SD socket.. and I didnt do anything with AREF yet.. just using a cap and tying to GND is ok?
(I dont need to tie that to any voltage reference point?  (ie: the 3.3v line at all?)



Lastly...  (caps).. still a bit confused on these..

from the schematic,...it looks like ALL the caps used are polarized ones??  (or am I reading the symbol wrong?.. I dont see any +/- on the cap symbols anywhere?)

I thought the CAPACITOR symbol that had two STRAIGHT lines.. meant a regular old cap.. and a CAPACTOR symbol that had  stiaght line and 1 rounded line.. was signifying a POLARIZED cap?

is this true? (or am I under the wrong impression?)


in this case.. then ALL caps used her should be polarized?


thanks!..


Oh and Robert.. the pcb design/layout is appreciated.. but when I show you the space and size (shape) of the PCB.. you'll probably just laugh at me!  lol

thanks again!

we'll post when I get to work..and open things up again.





oric_dan

#16
Nov 30, 2012, 08:39 pm Last Edit: Dec 01, 2012, 12:52 am by oric_dan(333) Reason: 1
Despite what the symbol is, caps less than 1 uF are typically unpolarized, and >= 1 uF
are typically polarized.

dhenry

Quote
what IS the minimal (but still somewhat stable/safe) components needed?


A minimum implementation would include just the chip itself.

A reasonable minimum implementation would have a decoupling cap, a crystal + two caps, or a decoupling network on the analog supply. And then more from there, based on your needs.

I have done many "chip-only" minimum implementations myself.

xl97

hi..
thanks for the reply..

this can not (should not) be a chip by itself project... IMHO.. 

I mean I need it to be small.. but I want it to work and be somewhat stable!  lol


Since it will be running @ 3.3v & INTERNAL 8Mhz clock...  I dont need the caps/crystal.......correct?

RESET pin broken out (for easier flashing/uploading)
DTR pin broken out (for easier flashing/uploading)

AREF pin (correctly set-up... I see in the schematic Crossroads posted.. he has the AREF pin connected to GND through a cap... but I do NOT need to connect to the 3.3v for a voltage refeence?  Just keep it INTENRAL reference at the 1.1v or whatever?)

and of course I want to ensure that I 'correctly' set-up the battery/power input..

since there will NOT be any voltage regulator (battery supply will be within the 3-3.7v range max).. but I want it to be stable..no ripples.

follow same principles or ceramic/polarized cap on the input power lines?



@ oric_dan(333)
Quote

Despite what the symbol is, caps less than 1 uF are typically unpolarized, and >= 1 uF
are typically polarized.


thanks!.. rules like this help a noob like me.

I am still wrestling with 'decoupling'.. and 'KNOWING' when to use a certain component or not (like when to use ceramic vs polarized..etc)

hopefully I can get to a more final version tonight/tomorrow.. and I'll post for review..

appreciate all the discussion guys!

thanks!  :)

CrossRoads

The little ceramic decoupling caps are not polarized.  Example:
http://www.digikey.com/product-detail/en/C0805C104K4RACTU/399-1167-1-ND/411442

Rule of thumb/general guidance: 0.1uF cap on every Vcc/Avcc pin on every part located as nearby as possible.

Aref - needs a 0.1uF cap to Gnd if you are using the internal references
See 2.2:
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.

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