DDS (generating sine waves) with onboard DAC using latest PIC 16F chips?

[Mike, K8LH]

Do you think it might be possible to add 2 (or more) bits of precision to the DAC?

Interval  #1  #2  #3  #4
     DAC  00  00  00  00  -> 0.00v
     DAC  00  00  00  01  -> 0.04v
     DAC  00  00  01  01  -> 0.08v
     DAC  00  01  01  01  -> 0.12v

     DAC  01  01  01  01  -> 0.16v
     DAC  01  01  01  02  -> 0.20v
     DAC  01  01  02  02  -> 0.24v
     DAC  01  02  02  02  -> 0.28v

     DAC  02  02  02  02  -> 0.32v
     ........

[HankMcSpank]

Do you think it might be possible to add 2 (or more) bits of precision to the DAC?

Interval  #1  #2  #3  #4
     DAC  00  00  00  00  -> 0.00v
     DAC  00  00  00  01  -> 0.04v
     DAC  00  00  01  01  -> 0.08v
     DAC  00  01  01  01  -> 0.12v
 
     DAC  01  01  01  01  -> 0.16v
     DAC  01  01  01  02  -> 0.20v
     DAC  01  01  02  02  -> 0.24v
     DAC  01  02  02  02  -> 0.28v
 
     DAC  02  02  02  02  -> 0.32v
     ........

This must have slipped past me - I'm not understanding what you're getting at?

I was actually wondering myself whether it's possible in practise to squeeze another 2 bits of effective' resolution by switching the fixed voltage reference supply into the DAC resistor divider chain (ie feed 1.024V in for the first 32 voltage level steps, then 2.048, then 4.096V) - it might be a bit spikey (due to the FVR switching voltages), but if not that should mean we can squeeze 7 bits out of the PIC's DAC pin.

[rmteo]

Use a DDS chip.

[HankMcSpank]

Use a DDS chip.

They're overkill for my needs (I only want an audio waveform at about 5khz frequency max! They typically go up to Mhz...so i'm paying handsomely for a feature I don't need) - I also want intricate 'control' over how to select the final waveform via my own control set (not be forced to follow theirs) ....plus if we all simply used dedicated hw ICs (at $15 a pop!) what would we ever learn?

[rmteo]

Using the right tool for the job is half the battle won - that is what you learn. Here is a 20KHz Sine Wave generated by using the built-in 12-bit DAC of the MCU which like any peripheral (such as a timer or ADC) uses little to no CPU resources once set up. Without a proper DAC, generating waveforms will consume substantial amounts of CPU resources. However, for any practical application, I would still use a DDS chip.

[HankMcSpank]

Using the right tool for the job is half the battle won - that is what you learn.

Agreed, and paying $15 for a DDS IC, that I can (hopefully) get a $1 PIC to fulfill my (modest) needs means I am indeed trying to use the right tool for the job - i wouldn't use a rotavator to dig over my garden when for my tiny bit of soil a spade is just fine (while a rotavator clearly turns soil over, I'd say it wasn't the right tool for the job in that instance)

Here is a 20KHz Sine Wave generated by using the built-in 12-bit DAC of the MCU which like any peripheral (such as a timer or ADC) uses little to no CPU resources once set up.

Again, I don't need to generate 20khz (that's 4 times higher than I need), I don't need 12 bits resolution (that's about 5 or 6 bits more than I need).

But more importantly, I don't learn a thing if I go & buy a DDS IC (& at the end of the day, isn't that why most of us do this type of stuff?)

[rmteo]

Well I did use a $1 MCU to generate that sine wave. So by your logic, that would be the right tool for the job.

[ScaleRobotics]

On a side note I see there is a future product with an 8 bit DAC. Im on my phone, so I can't tell if there is even a dataxheet out for it. Pic16f1786 is one of them.