DAC IC vs Resistor ladder

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Hello,

 

I want to know the different between resistor ladder and DAC IC, If I use precise resistors(1%). Regardless the communication protocol that DAC IC provides what are their advantages ?

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jkl;

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

Last Edited: Mon. Jun 24, 2019 - 08:32 AM
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Note that if you use resistor networks, multiple resistors all in the same package, they tend to match each other very well.  They may not be on value, but they'll all be off by the same amount and in the same direction (within reason).  So if you're saving a nickel there, keep that in mind. 

 

DAC chips also have (and need more) buffers. Spend the euro or two and buy a real chip.  Dealing with the hassle of building your own is not worth it.   S.

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alex20 wrote:
I want to know the different between resistor ladder and DAC IC
Well a DAC usually has a 2 or 3 wire interface. A resistor ladder uses 8 or more of your micro's GPIO pins. So often choosing a DAC is about saving MCU pins.

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With your r-2r ladder, it's VERY touchy getting all the resistances right. 

 

In junior college, I made one out of 20-turn trim pots I found in a parts drawer. I adjusted them all with an ohm meter, then made a program to output a sawtooth waveform. On an oscilloscope, I could pretty easily see which pots were off and tweak them.

 

The results were pretty lousy, but good enough for drawing pictures on an oscilloscope or chart recorder.

The largest known prime number: 282589933-1

It's easy to stop breaking the 10th commandment! Break the 8th instead. 

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If you only want a few bits (say 4 or 5), you can buy a cheapo resistor network, with decent matching.  Otherwise, get a cheapo 8 bit dac. In any case, more than 8 bits is completely out of the question.

Even the pin voltage levels won't match exactly, so having 0.00001% resistors wouldn't be the end of the story. 

 

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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There is also the alternative of low-pass filtering a PWM signal: https://www.allaboutcircuits.com...

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LTC2644 Datasheet and Product Info | Analog Devices

Dual 12-/10-/8-Bit PWM to VOUT DACs with 10ppm/°C Reference

 

"Dare to be naïve." - Buckminster Fuller

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"Dare to be naïve." - Buckminster Fuller

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I recommend going to eBay and getting a 10-pack of these PT8211 chips.  They are dual 16-bit resistor-ladder-based DACs that sell for 18 cents each (Euros, American, Canadian, Australian dollars, it doesn't matter at this price) !https://www.ebay.com/itm/10pcs-P...

 

They use  SPI mode 0 interface to the AVR.  Values are signed 16-bit so with Vcc 3.3V the lowest output is for value: 0x8000 , which give Vcc/3 as the lowest DAC voltage.   Value FFFF is one bit below the mid point (Vcc/2) :  0000 is mid analog voltage (Vcc/2) : and 7FFF is the max DAC output voltage (  [Vcc/3]*2 ).

Last Edited: Fri. Jun 21, 2019 - 09:01 PM
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kl;

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

Last Edited: Mon. Jun 24, 2019 - 08:33 AM
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Paulvdh wrote:
The datasheet only states a "Monoticity" of 16 bits Maximum. (Duh!), but no minimum is stated.

 

The PT8211 datasheet says it's "functionally equivalent" to the TDA1311 which has a more detailed datasheet. Maybe they have the same specs?

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 They are dual 16-bit resistor-ladder-based DACs that sell for 18 cents each (

I'd hardly think so, at least at that price.  I'd be surprised to even see an 8 bit dac at that price, let alone one 256 times as accurate.

I suspect these parts have "terrible" DC accuracy (if you call  a few mv terrible)....but a few mv is much more than 16 bits.  Prob 8 bit accuracy, with 16 bit resolution.

For audio apps (20-20000Hz), you don't go down to DC, so it isn't as important, compared to instrumentation.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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jkop;

Doing magic with a USD 7 Logic Analyser: https://www.avrfreaks.net/comment/2421756#comment-2421756

Bunch of old projects with AVR's: http://www.hoevendesign.com

Last Edited: Mon. Jun 24, 2019 - 08:33 AM