Go Down

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

CrossRoads

A Large coin cell battery has these characterics:
Rated Voltage 3V
Capacity 225mAh

Not going to last very long driving an SD card.

"new 328P chips come programmed with the INTERNAL 8 mhz oscillator enabled,"
is divide by 8 also enabled by default, so it would run at 1 MHz?
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.

xl97

Thanks guys..



couple replies to the comments..

the Atmega328p (TQFP) was chosen 'for its look' in this particular situation..  (it was part of a 'prop')

I noticed what chip they used..mentioned what it was used for.. and it spawned  the idea to make a pcb for it.. and hence have the (initially only for looks) 328P be functional..and add some effects to the project in the end as well..

since the prop is already created.. and this is more or less a 'retro-fit'.. space is EXTREMELY small.. (and almost all components, but a few leds,. have to go on bottom as well!)


I am hoping to add in both serial and icsp pads for easier flashing.. but only if I can squeeze them in!..


timing (I dont think) is crucial.. (I guess Id have to check on the PWM Audio library I plan to use?). so 8Mhz without caps/crystal sounds right/perfect!...

And not having to use a regulator also helps on saving 'space/components'..

I 'do' however want a stable power source input for the chip though..

and what is this 'stale reference' for analog comment mean? can you explain a bit more please?


also wont breaking out/having both the rest pin and a dtr pad help in flashing both bootloader AND when uploading a sketch? (since there wont be any reset button to 'time' the uploading of a sketch on auto-reset?)



also Im not sure what this means?  (although it was aimed at me)

Quote

"new 328P chips come programmed with the INTERNAL 8 mhz oscillator enabled,"
is divide by 8 also enabled by default, so it would run at 1 MHz?



thanks!



Krupski


A Large coin cell battery has these characterics:
Rated Voltage 3V
Capacity 225mAh

Not going to last very long driving an SD card.

"new 328P chips come programmed with the INTERNAL 8 mhz oscillator enabled,"
is divide by 8 also enabled by default, so it would run at 1 MHz?


Lithium coin cells are usually 3.6 volts, not 3.0.

And a question: Does an SD card ALWAYS draw "full" current (even when chip select is not asserted)?

I would think you would select the SD card, read or write the data, then put it back to sleep.

There's no reason I can think of for any flash memory card to ALWAYS draw full current.
Gentlemen may prefer Blondes, but Real Men prefer Redheads!

Krupski


and what is this 'stale reference' for analog comment mean? can you explain a bit more please?


The 328P has a built in regulated 1.1 volt reference for the A/D converter. It will be 1.1 volts regardless of VDD.

If you use a plain 3.6 volt coin cell and select the internal reference, it will work... no regulator needed (and besides, any regulator just wastes the excess power as heat... even switchers).

Gentlemen may prefer Blondes, but Real Men prefer Redheads!

CrossRoads

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.

Go Up