Filtering noise from a wire

[Ioannis]

Even if you have the fastest MCU to decode rotary encoder, the bottleneck is the I/O expander and will not be fast enough to follow users speedy fingers!

Ioannis

[Demon]

Even if you have the fastest MCU to decode rotary encoder, the bottleneck is the I/O expander and will not be fast enough to follow users speedy fingers!

Ioannis

This is a signal from an EC11 rotary encoder.

5vdc with 10:1 probe
.1 volt / division
.2 ms / division




It takes about 2.5 time divisions to activate; so about 0.5ms.

MCP23017 I/O Expanders can run up to 1.7 MHz in I2C mode.
MCP23018 I/O Expanders can run up to 3.4 MHz in I2C mode.
MCP23S17 I/O Expanders can run up to 10 MHz in SPI mode.

I'm not keen on the new addressing mode on the MCP23018 version. I'm hoping the MCP23017 is fast enough at 1.7 MHz in I2C mode. At worse, I'll learn how to use the MCP23017 at 10 MHz in SPI mode.

(nope, haven't done any math to check if it's possible, mainly cause I have no clue how to do that properly )

[tumbleweed]

MCP23017 I/O Expanders can run up to 1.7 MHz in I2C mode.
MCP23S17 I/O Expanders can run up to 10 MHz in SPI mode.

That's the wire speed... you'll never get the code to run anywhere near that fast except for a single byte transaction.
You won't get I2C to run that fast without active pullups, and getting the PIC to do 10MHz SPI depends on your system clock.

[Demon]

...You won't get I2C to run that fast without active pullups...

What do you mean by active pull-ups? I couldn't see a meaningful description on google.

I'm not using weak internals, I'm using 4K7 externals.


EDIT: ... aaaaaand .......


This pops up as soon as I posted my question:

For the next guy, this is active pull-ups.

https://picaxeforum.co.uk/threads/i2...-values.32111/

[Demon]

The graph at the bottom of page 1 of the LTC4311 shows a total rise-time of about 1uS.

https://www.analog.com/media/en/tech...ets/4311fa.pdf

Would a LTC4311 be enough to process a rotary encoder with an MCP23017?

Would I be able to use I2CRead and I2CWrite with this device, or would I have to use another technique?


The 16F1946 is rated up to 400kHz according to Table 24-4, but there's this note under the table:

Note 1: The interface does not conform to the 400 kHz specification (which applies to rates greater than 100 kHz) in all details, but may be used with care where higher rates are required by the application.

https://ww1.microchip.com/downloads/.../40001414E.pdf


(I'm using MCP23017 which are rated for 100kHz, 400kHz and 1.7 MHz)

[rsocor01]

The graph at the bottom of page 1 of the LTC4311 shows a total rise-time of about 1uS.

That graph shows a rise time of 1uS by only using a 15.8k pull-up resistor. It also shows that by using the LTC4311 you get an almost perfect waveform. It looks like this LTC4311 chip is exactly what you need for your application. I would pay special attention to where this chip should be placed in the PCB board. Example, closer to the PIC, or closer to the I/O expander, or closer to the resistors, etc. If you find the answer to this question please let us know.

[Demon]

Thanks, that's what I was hoping.

Just checked and JLCPCB doesn't have any in stock. They don't have any other I2C accelerator chips (that I can see). Now I understand the gripes on the interwebs about the cost of this chip.

I can get it by JLCPCB's global purchase program, but I won't be paying that "JLCPCB price".


And it doesn't exist in DIP format, so I can't do a quickie test.

[Demon]

...I would pay special attention to where this chip should be placed in the PCB board. Example, closer to the PIC, or closer to the I/O expander, or closer to the resistors, etc. If you find the answer to this question please let us know.

My plan was to keep the resistors and accelerator chip right up against the PIC.

I don't recall seeing location requirements, but I wasn't looking for that info last night either.