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I want to generate 8 analog independent signals from a microcontroller, such as a BeagleBone or STM32. In my research, I found that I can use an external multi-channel DAC and interface it with the microcontroller via SPI.

However, I always found that the output signals or a part of them are connected to each other. They will give me the same signal which is not what I want. I want 8 completely independent signals. In other words, I want to be able to generate 1, or 2, or any number of analog lines, each with their own independent voltage level. If any one has an idea how to do that I will be thankful if he helps me. Thank you.

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closed as unclear what you're asking by Daniel Grillo, PeterJ, Scott Seidman, nidhin, Vladimir Cravero Mar 6 at 13:05

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question.If this question can be reworded to fit the rules in the help center, please edit the question.
2  
Can you show us what you mean with "output signals connected to each other"? Is that the behavior of a specific part you found? DACs shouldn't normally behave like that. – Vicente Cunha Mar 1 at 11:59
    
That is mean they have the same voltage, for example the TLV5630 it has 8 ouput channels but they have the same voltage all of them. – oussama Mar 1 at 12:08
5  
If you use that DAC correctly you should have 8 independent outputs. – Steve G Mar 1 at 12:12
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What is the upper frequency of these signals? What accuracy and resolution? – Olin Lathrop Mar 1 at 12:14
1  
Um, OK, but what is the upper frequency of these signals? What accuracy and resolution? – Olin Lathrop Mar 1 at 12:28
up vote 4 down vote

Here are some ways for a microcontroller to produce analog signals:

  1. Built in D/A. Some have these, although they are not common.

  2. Filtered PWM. If your bandwidth * resolution requirements are low enough, this is a easy way to get analog signals. Many microcontrollers have PWM generation hardware built in, and you can trade off the resolution with the PWM period. A couple of poles of passive R-C low pass filtering after the PWM is usually good enough to attenuate the PWM frequency below the level you care about.

    Advantages of PWM are that it is low cost, largely built into the micro, linear, no "glitch energy", and doesn't suffer from uneven steps at major powers of 2.

  3. External D/As. There are chips that do this over various digital busses, like SPI, IIC, IIS and other interfaces. This will give you a higher bandwidth * resolution product than filtered PWM.

    There are many chips out there. Which one is appropriate for you depends on the resolution, bandwidth, and accuracy you need, and money you are willing to spend.

Each of these schemes produces independent analog signals per channel. A 8 channel D/A chip, for example, will be able to drive each channel with a independent signal.

However, you should step back and examine whether you really need analog signals. What will they be used for? Many things are more easily and more efficiently done with discrete pulses. If you want to control a motor, brightess-adjust LEDs, etc, most likely it is better to drive them with pulses. Even audio is commonly handled with pulses right up to the speaker, which is what class D amplifiers are about.

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1  
Ok maybe i should clarify the gool of the project i want to concept and realise an input/output module like ADAM6052 this module can generate analog and digital signals, now i am focusing on the analog signals there voltage is between -30V to 30V that is mean i fixe what voltage i want for example i want a 5V signal and what output channel i want send to for example channel 7 i run the program then i found a 5V voltage on the pin number 7 of the DAC or maybe i want to send multiple voltages to multiple channels for examples 7 volt to channel 1 and 10 volt to channel 3 at the same moment – oussama Mar 1 at 12:41
up vote 0 down vote

The TI DAC088S085 is one of many independently controllable DACs. http://www.ti.com/lit/ds/symlink/dac088s085.pdf

There are quite a few DACs listed on sites such as Digikey, Mouser, etc. Learning how to to drive the search engines on those sites can be a bit tricky, though, especially when you don't have a real good idea of exactly what you need.

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You seem to be using "DAQ" to mean "digital to analog converter". Usually it means something related to Data AcQuisition. Note that there is no Q in "digital to analog converter". – Olin Lathrop Mar 1 at 12:31
    
@OlinLathrop Yup. I've been working with a NI DAQ a lot recently, and those two acronyms sound the same in my head. Thanks! – CHendrix Mar 1 at 12:45

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