Help Choosing the correct PIC for 2 Channel PWM

[JimAvanti]

Hi,
I could use some help choosing the correct PIC. I need to have 2 independent PWM outputs to be used for generating two distinct tones. The only other thing required is to have two input pins to trigger the PWM outputs and a few inputs for dip switches to select the frequencies. I have spare 16f1938, 18F14k22 chips. I would like to keep the pin count as small as possible. The 16f1938 shows 3 ECCP ports, which I thought was all you need, but then it shows 0 for stand alone PWM. The Hardware PWM seems confusing to me once you go over one output so I want to make sure I am at least stating with a micro that can do what I need to do since I don’t really have enough hair left to pull out.
I am using PicBasic 2.6c

Thanks,
Jim

[HenrikOlsson]

Hi Jim,
As far as I can see the 1938 has three ECCP modules (for which HPWM might not work, I don't know for sure) AND two standard CCP (for which the HPWM command "should" work). And in the event you should find that HPWM doesn't work it's not that hard to setup manually - and it gives you more "power", like being able to have more than 8bits of resolution. I'll promise to help you out if you need, just make a post here.

So, if you already have the 1938 on hand and it's suitable from other perspectives then I'd use that.

/Henrik.

[JimAvanti]

Thanks Henrik. I will give it a try and let you know if (When?) I run into problems.

Jim

Hi Jim,
As far as I can see the 1938 has three ECCP modules (for which HPWM might not work, I don't know for sure) AND two standard CCP (for which the HPWM command "should" work). And in the event you should find that HPWM doesn't work it's not that hard to setup manually - and it gives you more "power", like being able to have more than 8bits of resolution. I'll promise to help you out if you need, just make a post here.

So, if you already have the 1938 on hand and it's suitable from other perspectives then I'd use that.

/Henrik.

[peterdeco1]

I don't think you will be able to generate 2 distinct tones. From the PBP manual:

Frequency is the desired frequency of the PWM signal. On devices
with 2 channels, the Frequency must be the same on both channels.

[HenrikOlsson]

That's a very valid point, one that I totally missed when reading Jims initial post, sorry about that!

That limitation comes from the fact that the CCP module(s) are (historically) tied to the same timebase so they need to have the same output frequency. Thankfully things have changed over the years and the CCP modules on the 16F1938 can individually be assigned any of TMR2/TMR4/TMR6 as their timebase. It does however mean that HPWM is out (at least I Think it is) and you'll need to setup the CCP modules manually.

/Henrik.

[JimAvanti]

So that means directly writing to the correct ports might do what I want? I didn't start testing yet. I did purchase an LED 3 channel 8-bit PWM driver to try (TLC59731DR). I thought it was SPI, but it isn't, and It also controls duty cycle. There are plenty of external devices available that look like they might work, but I'll wait until after I rule out the 16F1938 as an option.

Thanks

That's a very valid point, one that I totally missed when reading Jims initial post, sorry about that!

That limitation comes from the fact that the CCP module(s) are (historically) tied to the same timebase so they need to have the same output frequency. Thankfully things have changed over the years and the CCP modules on the 16F1938 can individually be assigned any of TMR2/TMR4/TMR6 as their timebase. It does however mean that HPWM is out (at least I Think it is) and you'll need to setup the CCP modules manually.

/Henrik.