DAC with m64

Log in or register to post comments
Go To Last Post
13 posts / 0 new
Author
Message
schamton
schamton's picture
Level: Hangaround
Joined: Wed. Feb 17, 2010
Posts: 157 View posts
#1
Posted by schamton: Thu. May 5, 2011 - 04:37 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hello,

I'm using an atmega64 and need to output analog values to be measured by another device. I have 2 ports (A & C) completely free, so I have already used 2 x R2R ladders to get 2 analog values.

The problem is i need more than 2 (let's say, about 8 ), so the R2R ladders are not my solution.

I'm thinking of maybe using MCP4921-E/P (Mouser part#) and SPI, but i'd need 8 of these..

What would you recommend using?

Thank you!

- Eric

Tags:

AVR Microcontrollers, megaAVR and tinyAVR, ATmega64
Top
leon_heller
leon_heller's picture
Level: Raving Lunatic
Joined: Fri. Jul 27, 2001
Posts: 7672 View posts
Location: St. Leonards-on-Sea (UK)
Posted by leon_heller: Thu. May 5, 2011 - 04:47 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Can you use PWM for the analogue outputs?

OTOH, I've quite sure that I've seen four DACs on one chip, so you could just use two of those.

Or, multiplex a single DAC with several capacitors to hold the values. A bit like sample and hold with an ADC.

Leon Heller G1HSM

Last Edited: Thu. May 5, 2011 - 05:54 PM
Top
schamton
schamton's picture
Level: Hangaround
Joined: Wed. Feb 17, 2010
Posts: 157 View posts
Posted by schamton: Thu. May 5, 2011 - 05:18 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I've never used PWM yet (one of the items in my to do list!)

I'll look for a chip with a greater number of outputs. I wrongly assumed that once i'd send a value through the SPI, the value would stay there until i'd send another one (5 sec intervals). Could you expand a little on the "multiplex a DAC with a capacitor to hold the value"?

Thanks Leon,

- Eric

Top
jgmdesign
jgmdesign's picture
Level: Moderator
Joined: Mon. Mar 19, 2007
Posts: 18675 View posts
Location: Long Island New York
Posted by jgmdesign: Thu. May 5, 2011 - 05:25 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

For the cost of the components use the dedicated DAC's. It is easier to code SPI to handle things than a boatload of passive components.

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

Top
leon_heller
leon_heller's picture
Level: Raving Lunatic
Joined: Fri. Jul 27, 2001
Posts: 7672 View posts
Location: St. Leonards-on-Sea (UK)
Posted by leon_heller: Thu. May 5, 2011 - 05:53 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Microchip has some new DACs that hold their value indefinitely.

Here is a quad DAC:

http://www.maxim-ic.com/datashee...

Look at sample and hold ADCs. My idea is similar and involves an analogue multiplexer and multiple capacitors to hold the charge.

Leon Heller G1HSM

Top
jgmdesign
jgmdesign's picture
Level: Moderator
Joined: Mon. Mar 19, 2007
Posts: 18675 View posts
Location: Long Island New York
Posted by jgmdesign: Thu. May 5, 2011 - 06:00 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Leave it to Leon to drag the "M" word into stuff. :)

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

Top
Bronze Markbobgardner
bobgardner's picture
Level: 10k+ Postman
Joined: Wed. Sep 4, 2002
Posts: 26609 View posts
Location: Orlando Florida
Posted by bobgardner: Thu. May 5, 2011 - 06:01 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

LT and Analog an National and TI all have octal or quad SPI DACs.

Imagecraft compiler user

Top
jgmdesign
jgmdesign's picture
Level: Moderator
Joined: Mon. Mar 19, 2007
Posts: 18675 View posts
Location: Long Island New York
Posted by jgmdesign: Thu. May 5, 2011 - 07:56 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

@ BobGardner

Good point. One interface to one chip and have a nice day.....err CODE :)

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

Top
schamton
schamton's picture
Level: Hangaround
Joined: Wed. Feb 17, 2010
Posts: 157 View posts
Posted by schamton: Thu. May 5, 2011 - 09:12 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

well, ok, whatever your issue with Microchip is :P

i think i'll go with this part TLC5628CN (mouser) since it has 8 converters and the one Leon suggested has 4.
http://focus.ti.com/lit/ds/symlink/tlc5628.pdf

thank you!!

- Eric

Top
jgmdesign
jgmdesign's picture
Level: Moderator
Joined: Mon. Mar 19, 2007
Posts: 18675 View posts
Location: Long Island New York
Posted by jgmdesign: Fri. May 6, 2011 - 02:23 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

@schmanton.........

Ypu have no idea the issue with microchip/Leon this community has.

I do give Leon credit for honest, and intelligent responses though. Even if he tout's the dark evil empire

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

Top
leon_heller
leon_heller's picture
Level: Raving Lunatic
Joined: Fri. Jul 27, 2001
Posts: 7672 View posts
Location: St. Leonards-on-Sea (UK)
Posted by leon_heller: Fri. May 6, 2011 - 04:55 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I use AVRs as well, and lots of other MCUs. Many people here are paranoid about Microchip, probably because PICs outsell AVRs.

Leon Heller G1HSM

Top
MBedder
MBedder's picture
Level: Raving Lunatic
Joined: Mon. Nov 2, 2009
Posts: 3219 View posts
Location: Zelenograd, Russia
Posted by MBedder: Fri. May 6, 2011 - 12:01 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

leon_heller wrote:
...probably because PICs outsell AVRs.
Not anymore. In a last quarter the Atmel has raised the MCU sales to $294M (+95% to 1Q 2010), whereas the Microchip got $261M (+17% to 1Q 2010). According to this, Atmel now is #3 and Microchip is #4 MCU supplier in the world.

Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

Top
leon_heller
leon_heller's picture
Level: Raving Lunatic
Joined: Fri. Jul 27, 2001
Posts: 7672 View posts
Location: St. Leonards-on-Sea (UK)
Posted by leon_heller: Fri. May 6, 2011 - 12:44 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I referred to PICs and AVRs, not total sales. Atmel has always been ahead in total revenue - it's a much bigger company.

Microchip has been #1 and Atmel #5 for the last few years for 8-bit devices. Has that changed?

Leon Heller G1HSM

Top