Alternate D/A converter

Go To Last Post
19 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Greetings!!

Somebody out there spare me some research! I am using a MAX522 8pin SPI D/A converter. It is a dual unit, and it works great. Trouble is, that it is damn expensive in small quantities here in the states($5.00each).

Does anyone know of an 8bit, SPI, 8pin device that is lower in cost? It does not need to be a dual as I am only using one output. Oh yeah, it needs to operate on 2.7-5vdc

DIP package preferred

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

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I guess we need to know more of your constraints. If I go to the
Analog Devices website, products -> DA converters, parametric
search, enter SPI and 8 bit resolution as constraints, I get 18
matches. The cheapest match is the AD5601 which comes in a tiny
SC-70-6 case. Digikey sells it for USD 2.38 for a quantity of 1.

I'm sure other vendors have similar offers.

Jörg Wunsch

Please don't send me PMs, use email if you want to approach me personally.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks for the info, I admit I am beig lazy here. I was just asking since you can usually get more from a broadcasted thread to the world as opposed to going on a silicon search

Thanks again

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

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

What I do for a DAC, just use a RC lowpass filter on a pwm output from the AVR. Then you can just set in a register from 0 to 255, or probably better resolution using the 16bit counter. You probably want the highest frequency, and trade noise for update rate for power usage when picking the values for C and R.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Good Idea, but i need the resolution, and accuracy as i am gauging a thermistor. This is a thermometer that is running my attic fans as part of my home automation system.

Keep the ideas coming!!

Jim :mrgreen:

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

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thermometer sounds like a job for an a/d to me. How does the hi res d/a come into play here again?

Imagecraft compiler user

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
Thermometer sounds like a job for an a/d to me. How does the hi res d/a come into play here again?

Bob:
Maybe Hi-res is not the proper term. I am building a total home automation system, skilight control, lights, heat, a/c etc. My attic hits over 135' in the summer with the sun beating on the roof(you being a Floridian can relate!). The house becomes very hot as a result. When the attic fan is turned on, it cools the attic extremely well, and the house too. my thought is twofold, one, monitor the temperature, and if it gets above a certain threshold, turn the fan on automatically. Two, since this node is part of the home network, it can relay the temperature back to the host cpu(Mega162 with 64k of external RAM and EEprom) for display on the remote terminals in the house. The host cpu can also turn the fan on through the node network so the house is cool when my wife gets home.

Why i need the d/a is because the at90s2313 does not have an a/d internally, but it does have a comparator. I have a thermistor sensing circuit that provides an analog voltage to one input of the comparator. THe other input is tied to the d/a. by incrementing the d/a until I get a comparator match, I can then do a simple binary to bcd conversion and display the temperature.

The micro also has a sensor for the attic stair door that shuts the fan off should the door open so no one puts their hand in the blades accidentally. and turns on the attic lights as well.

I know this sounds complicated, but it really is not.

Maybe I should open a project page in that area of the Freak site. Can I post the nodes, cpu, code and documentation as I complete them?

Incidentally, in case anyoone is wondering why I just don't use an AVR with a built in a/d, the reason is i have a boatload of the older 2313's and I want to use them up.(My wife is also not letting me buy more stuff at the moment - DAMN!! :oops: )

Regards,
Send Comments - PLEASE!!

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

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Since you have so many 2313 couldn't you use a port on one of them and make a R/2R resistor ladder?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Yes, I could do that, but that is a pain in the ass. The d/a is an 8pin spi device. I can create a simple bit-bang spi port on the 2313. the only thing that sucks is that d/a's in 8 pin dips cost around $5.00 each. Oh well.

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

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You can read a string of dallas 18b20 thermometers... one in the attic, one outside, one in the house using 2 pins... (alternate plan, less analog, more digital)

Imagecraft compiler user

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Maybe I misunderstood...
My thought was to feed the result of R/2R ladder to analog comparator of same 2313, the other signal to comparator being the temperature voltage and then do a bit-bang SPI on same chip (if that's needed, I suppose you wan't to turn on fan with a relay?).

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

bobgardner wrote:
You can read a string of dallas 18b20 thermometers... one in the attic, one outside, one in the house using 2 pins... (alternate plan, less analog, more digital)

I am going to have to look at that part. Great idea as it eliminates the thermistor, and the dual op-amp circuit I am using now. I never thought of that. How much are the devices?

Lennart:
Yes, the fan and the lights are relay controlled.

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

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Don't know if you have seen this app note...
http://www.atmel.com/dyn/resourc...

BTW, I have built something "same but different" that you are aiming at. I don't control any lights but an heating system with mega16 as the host and AT90S2313 as remote devices (I also had a bunch of them).
I measure 7 NTC's (they are very cheap and can use long tiny cables), send results to mega16 ADC. Then use I2C to send computed results to slaves that display temperatures on LCD, control a circulation pump and movements of a shunt motor.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

For reading a thermistor, it seems like using the 16 bit timer1 pwm with the comparator would be an accurate, elegant, low parts count solution. (thermistor, two resistors, and a capacitor)

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

What about a resistor ladder on PIO pins? Obviously not as good as a IC-DAC but its certainly cheap!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hey Bob,
Those converters look cool. A little software intense, but I could deal with that. The TO-92 package is great. Could you give me a pointer on converting the 9bit temp from C to F? Me and math are not the best of bud's.

Also, I code in assembler. I suck at 'c'. Until I can get Smileys book and butterfly combo I am gonna be a little challenged.

Thanks
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

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Bob:
I am looking at the dallas part and I like what i see. The only issue is it does look a tad software intense as I suspected. I downloaded the app notes. but do you have any code I could look at?

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

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

They read out directly in 9 bits of 'quarter degrees' C. I will leave conversion to F as an exercise for the reader. Several projects show reading 'onewire' protocol... check out microsyl.com

Imagecraft compiler user

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

great
thanks

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