Understanding DAC column of microcontroller guide

[treez]

Hello,
In the DAC column of the following product selector guide, "5b/8b/9b" presumably means "5 bit/8bit/9bit"?

Microchip product selector guide...
**broken link removed**


We can't find a single microcontroller that has all our requirements because none have 3 DAC outputs, and so they all need an external DAC IC, which needs to be communicated with via a serial module, and none of us can use serial modules on microcontrollers....therefore, do you believe we are better off using two microcontrollers?......one with the three DAC modules on it that we need, and the other with all the other stuff (ADC's digital I/O, PWM outputs etc) that we need?

 

[horace1]

Hello,
In the DAC column of the following product selector guide, "5b/8b/9b" presumably means "5 bit/8bit/9bit"?

Microchip product selector guide...
**broken link removed**


We can't find a single microcontroller that has all our requirements because none have 3 DAC outputs, and so they all need an external DAC IC, which needs to be communicated with via a serial module, and none of us can use serial modules on microcontrollers....therefore, do you believe we are better off using two microcontrollers?......one with the three DAC modules on it that we need, and the other with all the other stuff (ADC's digital I/O, PWM outputs etc) that we need?

if you have two microcontrollers you have the problem of how do they communicate? e.g. UARTs, SPI, I2C, CAN, Ethernet, WiFi, etc
there are problems of synnchronisation, master/slave, peer to peer or client/server relationships, etc
I would think it simpler to use a Microcontroller with an external quad DAC such as the Analogue Devices DAC8420 or TI DAC7716
OK you have to learn how to use SPI (there is plenty of example code on the web) but I think that would be far simpler than processor to processor communication

 

[wade_hassler]

I saw at least one p/n(PIC16F1788 ) with four DACs on that list, and the same part has 4(!) 16-bit PWM channels. These could be used as DACs .

Looks like your electronic design is done and the engineering must begin!

 

[treez]

I looked at the PIC16F1788 and it has no PWM outputs...

**broken link removed**
(top of page 8 = pic16f1788)

it has the "PSMC" output but this isnt a PWM output as such....ie you cant just shovel in a value into a duty cycle register, and another value into a frequency register and job done.

Also, its DAC's are 5 bit, whichmeans with a 5V reference, the resolution is 5V/32 = 150mV which isn't too good.....we need it to be at least 30mV per step

 

[FvM]

I saw at least one p/n(PIC16F1788 ) with four DACs on that list, and the same part has 4(!) 16-bit PWM channels. These could be used as DACs.

If 5-Bit DAC resolution is sufficient...

 

[horace1]

also does the One 8-Bit and three 5-Bit Digital-to-Analog Converters (DAC) meet your requirements? they seem low precision for a DAC these days

 

[treez]

no its too low precision....I like the idea of getting analog out from a PWM into RC...but surely that depends on the V(output high) level of the micro, and how close this is to the Vdd......if it cant switch up to vdd....then the pwm way of getting an analog out will be inaccurate...I mean supposing vdd=5v, but v(output high) for a digital pin is from 4.7V to 5v (tolerance) ....then youre going to get inaccuracy in the analog out that gets derived from PWM into RC.

 

[paulfjujo]

hello,

PIC16F1769 2 DAC 10 bits ...
or an external MAX541 in DIP8 DAC 16bits
dialogue with I2C protocole