Itsy Bitsy M0 outputs slight change in frequency when using

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RainySun
 
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Itsy Bitsy M0 outputs slight change in frequency when using

Post by RainySun »

Hey, I am currently using Itsy Bitsy M0 express, and I was able to output a PWM at 10Hz. When I use battery or a DC-DC converter to power the Itsy Bitsy using BAT pin, the output frequency is 9.7Hz instead of 10Hz. How can I resolve this issue. I hope to hear your response.
Below is the code I used to generate 10Hz.

import time
import board
import pwmio

Trig1 = pwmio.PWMOut(board.D10, frequency=10, duty_cycle=20000)

while True:
Trig1

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RainySun
 
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Re: Itsy Bitsy M0 outputs slight change in frequency when us

Post by RainySun »

I would also like to add that when I use battery to power Itsy Bitsy, the output I get is
For 5Hz, I get 4.85Hz
For 10Hz, i get 9.70Hz
For 50Hz, I get 48.49Hz

It looks like it has a factor of 0.97. I have tired making changes to the code but the issue is that with PWMIO, the frequency can only be written in Integers. How can I include the factor of 0.97 in the code? I hope to hear your response.

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Franklin97355
 
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Re: Itsy Bitsy M0 outputs slight change in frequency when us

Post by Franklin97355 »

What are you using to power the IB when you get 10hz?

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RainySun
 
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Re: Itsy Bitsy M0 outputs slight change in frequency when us

Post by RainySun »

I am using a DC Power Supply with voltage set to 5V, and current limit set to 100mAmp. I have also increased the voltage up to 5.5V to see if it make any difference, and it is still the same.

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adafruit2
 
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Re: Itsy Bitsy M0 outputs slight change in frequency when us

Post by adafruit2 »

this is likely due to the chip being off of USB which is how it synchronizes the internal clock. that said, thats a pretty big difference. do you have more than one board to test with?

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RainySun
 
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Re: Itsy Bitsy M0 outputs slight change in frequency when us

Post by RainySun »

Thankful for your response. I have two itsy bitsy M0 Express that I tested with, and both have the same response when using a DC power supply.
I will order ItsyBitsy M4, and test it with a DC power supply. I just realized if ItsyBitsy M4 doesn't have an internal clock (just like Itsy Bitsy M0), wouldn't it have similar response.

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adafruit2
 
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Re: Itsy Bitsy M0 outputs slight change in frequency when us

Post by adafruit2 »

yeah it might work :/ the 32u4 and nrf52840 do have xtals!

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RainySun
 
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Re: Itsy Bitsy M0 outputs slight change in frequency when us

Post by RainySun »

For ItsyBitsy M0 Express, is there anything I can do on the coding end to divide by 0.97 factor. For example:
These are the frequency that I will be using.
4.85 / 0.97 = 5Hz (to get the correct frequency output)
9.7 / 0.97 = 10Hz
48.49/ 0.97 = 49.9Hz

How do I divide the 0.97 on the code. I have used PWMIO function but I can only use integers. Can you please help me out with this.
I am sure this will help people out as well to output correct frequency when using a battery for M0 express.

Also, can you please confirm that ItsyBitsy nRF52840 works well with Circuit Python; not sure about ItsyBitsy 32u4.
I hope to hear your response.

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