Teensy 4.0 Pinout and SD Card/Ethernet Module Compatibility

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aminnie

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I have been running a custom built midi solution for the last five years. The solution involves two Teensy 3.2s and an LC. The Teensy 3.2s operate as an midi keyboard interface and sequencer respectively, and the LC as a 'Hammond' drawbar controller, 0.96 status screen, etc. Both Teensy 3.2s are equipped with PJRC SD adaptor cards and Wiznet WIZ850io/WIZ820io (forget which one!) ethernet modules that is integrated via MQTT to a Raspberry PI 3B+ that operates a 10" LCD touch screen enabling real time control of the solution. I am looking at upgrading to Teensy 4.x's and a newer Raspberry PI (less important).

Teensy 4.1 would be a gerat replacement considering that it supports both an SD card and ethernet. However, I would have to rebuild the solution. I noticed there is a comment on the PJRC site that the Teensy 3.2 and 4.0 pinouts are 'mostly' compatible. Minor pin incompatibilities can be handled. My question is two fold: Can I drop a Teensy 4.0 in place of a 3.2, and more specifically, would it be pin and functionally compatible with SD adaptor and Wiznet WIZ850io.WIZ820io ethernet module?

If the SD Card/Ethernet option is not compatible with the Teensy 4.0, then I will move on to the Teennsy 4.1 - a lot more work, but doable.

Thank you,

Anton
 
It really depends on the pinout and what precisely you use.

I put a basic list of the things that are compatible between the Teensys in the unofficial wiki:

Basically, the first serial port (pins 0/1), the first I2C port (pins 18/19), the position of the first 10 analog pins, the main ground, VIN, 3.3v, and VUSB pins are laid out the same, and the first SPI port (pins 11, 12, 13) are common among all Teensys.

Sound (either I2S or using digital to analog pins) is completely different between Teensy 3.x and 4.x.

Teensy specific optimizations for displays in the Teensy 3.x are completely different in Teensy 4.x. I don't recall if the 3.x ethernet support used similar Teensy 3.x SPI optimizations.

There is no analog reference voltage, nor is there is separate analog ground pin in the Teensy 4.x. The Teensy 4.x also does not have the inside pins AREF, A10, and A11 (but it does have VUSB).
 
Hi Michael,

Thank you for the details provided and the unofficial wiki reference. Good information and homework!

I took a quick look at the eletrcial connections for the SD and Ethernet modules (https://www.pjrc.com/store/wiz820_sd_adaptor.html) and the pinouts for 4, 9,10, 11, 12, 13 is the same as you mentioned. Not sure about any ethernet SPI optimizations though. Will review and compare with my implementation in the next few days to decide which path to take.

Much appreciated!

Anton
 
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