Thank you Netoperz:
I too want to quickly convert qty 6 of these boards to I2C bus, to
(1) cut down the I/O to each module to four connections,
(2) add PULLUP externals - running up to x cm over RJ11 24AWG telecom interconnect and
(3) bus up to 4 devices by shorting Address Pins to either +3.3 high or GND low.
I lifted the 522 NXP chip with my HotAir quite easily
but as I started to tape up the modules DuPont pin plastics with Kapton,
I had a great IDEA.
I am going to make a small square of KAPTON, slide it UNDER pins 1(I2C select) and 32(EA)
before I reflow the IC back into original position.
Intention: avoid trace cutting with knife ( I dislike working with my BinoScope and a Blade)
The pins are close , right at the corner.
I use Kapton Tape to protect areas and components from unintentional melting
within the vicinity of my hot-air rework.
I am going to try this .
The 001 image attached is just as I am sliding the Kapton tape into place with Red LED illumination,
the 002 image is with just the White LED
and third image is the Netoperz Instruction image with overlay where Kapton tape would be placed.
Summary
the (proposed, untested) concept is to insulate pins 1 and 32 at that corner,
reflow IC using hot air with pins 1 & 32 insulated/floating open,
and then use AWG30 to short/open pins 1 & 32 to Hi or Lo.
I will report back when I have hot air bonded the IC, and shorted using the (Netoperz) rework.
This will allow me to beta test I2C or UART modes on just one board,
discover Address Pin rework, and bus multiple units on I2C
and then see what cable distance I can get out of Telecom Satin patch cable and RJ11 interconnects.
If anyone has suggestions on pull-up values, let this audience know.
I think 27K is a good place to start.
As the fall back plan, if the module I2C bus idea fails,
I will go to a 4:1 SPI Mux using [MAXIM] 350... "old school" or use SS pins in grouped selection.
thanks Netoperz for your good discovery work, and I hope I can improve the rework
John Rad (CET-III, 39yrs)
UPDATE (SPI to I2C conversion of MFRC522 board, 08 FEB 2018):
I have bench down time to return to this project:
(1) new image with my USB microscope of the IC hot-air-resoldered.
(2) *some boards contain counterfeit IC's *
which do not have the correct product code when queried.
(3)I have Pin 1 and Pin 32 set for I2C mode and the Arduino I2C address query
per the Manufacturer Spec.
(I use #30 uninsulated stripped wirewrap on both floating pins)
discovery is pending:
?can the MFRC522 set to I2C and be recognized?
?can an IC with an incorrect house code (?counterfeit) operate in I2C mode?
