Filtering noise from a wire

[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.

[richard]

what problem is the active pullup bus chip going to solve ?
it will make zero difference to pbp's bit-banged commands and the mssp port would have no issues at 400kHz bus speed anyway [providing bus length and load is within reason] using the usual pullup resistors.

[Demon]

what problem is the active pullup bus chip going to solve ? ...

I was hoping:

- it would allow me to use the MCP23017 at 400MHz,
- it would be enough to read rotary encoders with an MCP23017,
- it would work using I2CREAD command.

But that's too many IFs. The chip is not available in DIP package for me to test.

I've since decided to go with a dedicated 16F1937 TQFP-44 at 32MHz with 36 IOC pins to manage my encoders. I have room for 14 encoders on this secondary PIC (primary is a USB PIC), and the jumper at bottom right will permit me to use a 2nd circuit if needed in the future.

I only need 13 for this first project. I could use the 2 pins for encoder #14 to create a 3 bit jumper, giving me addressing for 8 circuits (total of 103 encoders). I'll most likely make the change now that I've thought about it.




EDIT: I didn't forgetting mounting holes. The PCB will be mounted vertically along the perimeter of the enclosure with the pins pointed inwards. The high-mounted header pins will be easy to access. and a single line of hot-glue will secure the connectors.

[richard]

I was hoping:


- it would allow me to use the MCP23017 at 400MHz,
- it would be enough to read rotary encoders with an MCP23017,
- it would work using I2CREAD command.

MCP23017@400KHz , using a pic16 @32mhz can do that easily using mssp module
using I2CREAD command. @32 mHz the cmd will do 166KHz at best, even at 64 MHz it will not reach 400kHz

to read multiple rotary encoders with an MCP23017 the bus speed is the least of your problems , the hoops you need to jump through to track multiple edge transitions without error are extremely challenging.


re 16F1937 , why ? surely at least a 16f18875 would make tracking edges far easier. mind you its still difficult to keep track of more than one those 4 count per indent RE's
13 will be interesting. have you tried any code to be sure a result is even viable with the encoders you have selected ?

[Demon]

MCP23017@400KHz , using a pic16 @32mhz can do that easily using mssp module
using I2CREAD command. @32 mHz the cmd will do 166KHz at best, even at 64 MHz it will not reach 400kHz
..

I've never used MSSP. At least now I know where I stand using the command.

...to read multiple rotary encoders with an MCP23017 the bus speed is the least of your problems , the hoops you need to jump through to track multiple edge transitions without error are extremely challenging....

I am polling a controller for Flight Sim. I have multiple encoders on the circuit, but I do not expect more than 1 encoder to be active at the same time. I suppose with auto-pilot you could move 2 encoders at the same time, but there isn't an auto-pilot in this first plane (Cessna-152).

...16F1937 , why ? surely at least a 16f18875 would make tracking edges far easier. mind you its still difficult to keep track of more than one those 4 count per indent RE's
13 will be interesting. ...

Cost, size and availability at JLCPCB mainly. I want to make 100 units for the 1st batch, so every penny quickly adds up.

... have you tried any code to be sure a result is even viable with the encoders you have selected ?

Not yet. My breadboards are crap, and my mini-CNC is not as useful as I hoped.

I was going to get 5x PCBs from JLCPCB for testing. These are ordinary EC11 and EC10 (mouse wheel) encoders moved manually, it's NOT mechanically manipulated.

[Demon]

The controllers will look something like this:

[Ioannis]

Cost, size and availability at JLCPCB mainly. I want to make 100 units for the 1st batch, so every penny quickly adds up.

Well, why not select from Mouser or Digikey?

Ioannis