Topics

I2C display plus other I2C devices, 3.3V #ubitx

Rob French (KC4UPR)
 

Hello, I have one of the 20x4 LCD displays on my uBITX, with the I2C backup to free up pins.  I removed the two pull-up resistors from the (5V) backup, so that I could use it in conjunction with the SI5351.  

Question... so I can't recall which pull-up is now getting used to pull the I2C lines up to 3.3V, but I'm wondering, can I add another I2C device to this bus, without adding any other conversions?  

Specifically, I would like to use I2C to communicate between the Raduino and a Teensy 3.2 that I'm using for DSP audio filtering.  I was going to use serial, but I decided it was too much of a pain to try to interrupt the CAT stream, so I figured I'd try I2C instead.  But I want to make sure I can actually add the Teensy to the mix.

Thanks!
-Rob

Evan Hand
 

I have not yet done the mod, however KD8CEC at Hamskey.com has used the I2C line to link in second displays and Nano's for increased functionality.  To me that would imply that you can use the link to the Si5251.

FWIW
73
Evan
AC9TU

Jim Sheldon
 

Our group, the TSW actually had this working long before CEC used it and the only problem you might run into is the Si5351 can accept no more than a nominal 3.3V signal level on the I2C lines.  If you connect a device to the I2C bus that has pullups to the 5V supply on the data lines, you risk destroying the 5351.  Address wise, as long as you stay away from the 5351's I2C address, you can have more than one thing operating on the bus.  

Jim, W0EB

------ Original Message ------
From: "Evan Hand" <elhandjr@...>
Sent: 9/21/2019 8:38:00 AM
Subject: Re: [BITX20] I2C display plus other I2C devices, 3.3V #ubitx

I have not yet done the mod, however KD8CEC at Hamskey.com has used the I2C line to link in second displays and Nano's for increased functionality.  To me that would imply that you can use the link to the Si5251.

FWIW
73
Evan
AC9TU

johnrof@...
 

Easiest soln  is to use a two chan level converter (~50 cents). 
You can also make a 3.3 v device the master, with pullups to 3.3 v source.  Arduino will read 3.3 v as high.