Teensy 4.0 will not recognize I2C 7-segment display

pimp cauldron

New member
Hello friends,

I'm trying to get a Teensy 4.0 to recognize this display that uses an HT16K33 I2C driver chip:
https://www.adafruit.com/product/1270

The example (modified to scan all channels) I2C scanner will not recognize it, with the following output:

Code:
Unknown error at address 0x4CMCR:1 MSR:2001001, MIER:0 MDER:0 MCFGR0:0 MDMR:0 MCCR0:1928373b
Unknown error at address 0x4DMCR:1 MSR:2001001, MIER:0 MDER:0 MCFGR0:0 MDMR:0 MCCR0:1928373b
Unknown error at address 0x4EMCR:1 MSR:2001001, MIER:0 MDER:0 MCFGR0:0 MDMR:0 MCCR0:1928373b
Unknown error at address 0x4FMCR:1 MSR:2001001, MIER:0 MDER:0 MCFGR0:0 MDMR:0 MCCR0:1928373b
Unknown error at address 0x50MCR:1 MSR:2001001, MIER:0 MDER:0 MCFGR0:0 MDMR:0 MCCR0:1928373b
Unknown error at address 0x51MCR:1 MSR:2001001, MIER:0 MDER:0 MCFGR0:0 MDMR:0 MCCR0:1928373b
Unknown error at address 0x52MCR:1 MSR:2001001, MIER:0 MDER:0 MCFGR0:0 MDMR:0 MCCR0:1928373b
Unknown error at address 0x53MCR:1 MSR:2001001, MIER:0 MDER:0 MCFGR0:0 MDMR:0 MCCR0:1928373b
Unknown error at address 0x54MCR:1 MSR:2001001....
No I2C devices found

Scanning(Wire1)...
No I2C devices found

Scanning(Wire2)...
No I2C devices found

I've tried it with a variety of pullup resistor values from 1k to 4.2k, including no pullup resistors, on both SDA0/SDL0 and SDA1/SDL1. The "unknown error" messages will follow the display when I switch it between the bus channels.
I have another Teensy 4.0 I've tried which will also not recognize it. On a scope I can see an attempt to communicate at 3.3V on SDA as the error messages appear. But it looks like there is only about 1.5V across SDL and what looks like no response.
The display is powered with 5V from a 12v-5v DC-DC converter.

I can't get the Teensy to find the display via serial on CircuitPython either.

I am reasonably competent at soldering and I cannot find anything wrong with my work on the display and backpack.

Do you all have any ideas what I could be doing wrong? Is it possible I could have fried one or both Teensy I2C circuits by accidentally pulling up to 5V? I don't think it did it on both, though...

Many thanks!

2023-06-06 16.16.40 (Medium).jpg
 
I'm trying to follow your wiring in the photo and match it up to this Adafruit info

https://learn.adafruit.com/adafruit-led-backpack?view=all#1-2-inch-7-segment-backpack

Looks like you might have an external 5V power supply connected to the wires which go off the bottom side of the photo?

I can't quite see which Teensy pins get the yellow and green wires. Looks like yellow might be connected to pin 18 (SDA) and green is hidden from view but could be assumed to pin 19.
 
For the sake of testing, I would eliminate the uncertainty of external power and use a short USB cable connected directly to a PC or powered hub (which should be able to output 500mA) and connect the display's +5V power pin to Teensy 4.0 VIN/VUSB. I've used this chip before (but not as Adafruit's product) and it seems to always boot up without driving any of the LEDs, so even if your USB power isn't enough to turn on all the LEDs at full brightness, it should be fine to verify the I2C address.
 
OK, I got it to recognize the display. It turns out there are multiple problems with this setup.

I rewired everything for the sake of pictures and simplicity, and removed the power supply as you suggested Paul. This worked right away:
2023-06-07 10.58.48 (Medium).jpg

This, however, does not. I retried this just as an experiment. This is how I had it wired originally with two leads coming off the SCL/SDA pins to the pullup resistors to 3.3V.
2023-06-07 10.43.30 (Medium) (Medium).jpg

The display also does not work with this DC-DC convertor, which outputs 5.22V. I guess I will need to use a better regulated supply.
2023-06-07 09.51.53 (Medium).jpg

Thanks for your help!
 

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Have used HT16K33 based 7-seg and 16x8 displays powered with +3.3v on T3.2 - T3.6 with no problem.

Perhaps separate SCL and SDA wires.
 
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