several ICs on RPI pico

[Thomas-R-27]

Hello,
I am trying to run my RPI pico with a aht10 for measuring temperature and humidity, and a ENS160+AHT21 for reading the CO2, and a LCD2004 to display the data (I don't use the AHT21 on the ENS160 as its temperature is off by about 10C, as the ENS160 itself is self heating for accurate CO2 measurments). Application is controlling humidity, temperature and CO2 level in a mushroom growing box. All ICs work well separately (LCD alone, or ENS160/AHT21+ LCD, or AHT10 + LCD). The issue starts when I try to use the ENS160/AHT21 and the AHT10 together. They have the same address 0x38 so I have the ENS on IC0 (pins 0 and 1) and the AHT10 on IC2 (pins 6 and 7). The LCD runs on IC0, pins 16 and 17). I thought I could have several ICs on the same port as long as they don't have the same address; after all the ENS160/AHT21 have 2 ICs on IC0. Everytime I try to run all the ICs together I get the error message:
Traceback (most recent call last):
File "", line 29, in
File "/lib/ahtx0.py", line 50, in init
File "/lib/ahtx0.py", line 59, in reset
OSError: [Errno 5] EIO

If I remove the ENS or the AHT10, the program works again. Any hints? Code below, running with RPI_PICO-20250911-v1.26.1

many thanks for your comments!
Tom

AHT+ENS160+LCD.py

import time
from machine import Pin, I2C
from DIYables_MicroPython_LCD_I2C import LCD_I2C
import ahtx0
import AHT21
import ENS160

print ('Hello')
#LCD---------------------------------------------------------

The I2C address of your LCD (Update if different)

I2C_ADDR = 39 # Use the address found using the I2C scanner

Define the number of rows and columns on your LCD

LCD_COLS = 20
LCD_ROWS = 4

Create I2C object, Initialize I2C

i2c_lcd = I2C(0, sda=16, scl=17, freq=400000)
time.sleep(1)
lcd = LCD_I2C(i2c_lcd, I2C_ADDR, LCD_ROWS, LCD_COLS)
#LCD---------------------------------------------------------

#AHT---------------------------------------------------------

Create I2C object

#make sure to select 0 or 1 depending on which SCL/SDA is selected
i2c_aht = I2C(1, scl=7, sda=6)
time.sleep(1)

Create the sensor object using I2C

aht = ahtx0.AHT10(i2c_aht)

#AHT---------------------------------------------------------

#ENS160---------------------------------------------------------

Create I2C object

#make sure to select 0 or 1 depending on which SCL/SDA is selected

i2c_ens_aht = I2C(0, sda=0, scl=1)
time.sleep(1)

aht_ens = AHT21.AHT21(i2c_ens_aht)
ens = ENS160.ENS160(i2c_ens_aht)
ens.reset()
time.sleep(0.5)
ens.operating_mode = 2
time.sleep(2.0)

#ENS160---------------------------------------------------------

print("LCD: ",i2c_lcd.scan())

print("AHT: ",i2c_aht.scan())

#print("ENS_AHT: ", i2c_ens_aht.scan())

Define all Pins

led = Pin("LED", Pin.OUT)

#check Pins
led.on()
time.sleep(0.5)
led.off()
time.sleep(0.5)
led.on()

Setup function

lcd.backlight_on()
lcd.clear()

for i in range (0, 100):
temperature = round(aht.temperature, 2)
humidity = round(aht.relative_humidity, 2)
print (i)
lcd.clear()
lcd.set_cursor(0, 0) # Move cursor at the first row, first column
lcd.print('working '+ str(i)) # Display text at the first row
lcd.set_cursor(0, 1) # Move cursor at the first row, first column
lcd.print('temperature: '+ str(temperature))
lcd.set_cursor(0, 2) # Move cursor at the first row, first column
lcd.print('humidity: '+ str(humidity))
lcd.set_cursor(0, 3) # Move cursor at the first row, first column
lcd.print('working '+ str(i))
led.toggle()
time.sleep(1)

[scruss]

… the ENS160 itself is self heating for accurate CO2 measurements

How are you powering the setup? The ANS160 (datasheet) draws 79 mA on startup, which might be a little much for a USB-powered sensor board.

[Thomas-R-27]

Thanks! I just re-tried with a powered USB and get the same error message :-(

[robert-hh]

The first thing for me to check would be wiring (sda, scl, GND) and sufficent low pull-up resistors. If ghd wires are short, 4.7 k shoul be ok.

[Flipje1955]

To understand you correctly: you write: "I have the ENS on IC0 (pins 0 and 1) and the AHT10 on IC2 (pins 6 and 7). The LCD runs on IC0, pins 16 and 17)".
So you define IC0 with two different sets of addresses?

[robert-hh]

Two comments on the code:

• It is better readable, if you enclose it into line with three backticks If the first one ispy, then it is properly colored.
• and as @Flipje1955 said, you create the I2C(0) object twice at different pins. That's definitely wrong.

[Thomas-R-27]

Thanks for the comments. For the AHT10 it's I2C(1), not I2C(2) - apologies.

you create the I2C(0) object twice at different pins. That's definitely wrong.
How can I create the 3 I2C objects, 2 on I2C(0), one on I2C(1) (without using a TCA9548A I2C multiplexer)
many thanks!
Tom

[robert-hh]

You can connect several I2C devices to the same pair of sda/scl lines as long as the I2C addresses are different. So create just one I2C object and supply it to both drivers. Take care that they are not used both at exactly the same moment.

[Thomas-R-27]

OK so I could have:
i2c = machine.I2C(0, sda=0, scl=1)
with the ENS160/AHT21 and the LCD on I2C(0), sda=0, scl=1, correct?

unfortunately if I do that and connecting the working LCD to pins 0 and 1 (along with GND and +5V), using
devices = i2c.scan()
only detects [56, 83], which are the ENS160 and the AHT21, respectively. The LCD is not detected...

[Flipje1955]

can you re-establish the initial situation where you confirmed you could see the display was found by the scan when using it "standalone" (as in: no other devices on the bus) and from there reason what possibly changed when combining it with the ENS/AHT ?

[robert-hh]

Does the LCD use 5V levels or 3.3V levels for I2C? The Puco needs 3.3V.

[Flipje1955]

just looked at the LCD2004 I used for a project; I then recalled I applied 5V to get brightness but in order to do so, I had to insert 3.3V/5V voltage-level shifter for the I2C lines.....

[Thomas-R-27]

OK, I moved the ENS160 out, and got the LCD to work. Then I added the ENS and got this:
[39, 56, 83]
So it looks like it's working!
All is on 5V

[robert-hh]

The RPi Pico is NOT 5V tolerant. If all sensors work at 5V, use a 3.3V level shifter, suitable for I2C. Like this one https://www.adafruit.com/product/757.

[scruss]

It's mostly-kinda 5 V tolerant for inputs.

Unfortunately, those LCD panels need 5 V power for the backlight to work

[Thomas-R-27]

OK, sorry if I get a lot of "Don't do that!' but I use the 5V VBUS to power all I2Cs, and the 3.3V SDA/SCL from the pi to drive them. Maybe this explains some of the issues I have faced?

[scruss]

You're not going to get that from me. I've run these displays with 5 V power and 3.3 V logic for a long time

[robert-hh]

It is a question at which voltage level the I2C bus operates. Since the RPI Pico uses 3.3V levels, the bus must be operated at that level. As far as I could tell, the ENS160 and AHT10 use 3.3v Levels. The breakout board include a 5V->3.3V regulator, so you can supply the board with 5.5V, but the I2C signal level is 3.3V. The LCD is different. You must supply it at 5V to get a proper contrast, and the I2C level it expects and attempts to enforce is 5V. To have a clean and reliable bus operation, you then need a level shifter, but only for the LCD. @Flipje1955 showed his approach to it, and you have to do the same. Be cautious: There are different types of level shifters, and some do not work with I2C.

[Thomas-R-27]

Thanks! Usually, what power supply would you use for the other (non 5V LCD) I2C? The I2Cs like AHT10 seems to have very low power consumption, so the 3V3 SYS from the pi should work, correct?
Again, it's puzzling that most examples I found use 5V from VBUS to power ICs... thanks to all for your previous comments

[Thomas-R-27]

Thanks Robert. I have found many tutorials (including the one with the LCD library (DIYables_MicroPython_LCD_I2C) here: https://newbiely.com/tutorials/raspberry-pico/raspberry-pi-pico-lcd-20x4) that use the 5V VBUS from the pi and the SDA/SCL directly without level shifters. Is it bad practise or just "works well enough for an example"?

[Thomas-R-27]

BY the way the AHT10 says 1.8 to 6V and the ENS160 is 5V (or 3.3V if using the specific 3.3V on the IC)

[robert-hh]

Is it bad practise or just "works well enough for an example"?

This is bad practice, and it just works, as long as only one I2C device is connected. Assuming a 10kOhm pull-up resistors to 5V, it causes a back current into the Pico GPIO pin of about 100 uA when the level is high. Even if that most of the time will not break the pin circuitry, it is not an intended mode.

[robert-hh]

BY the way the AHT10 says 1.8 to 6V and the ENS160 is 5V (or 3.3V if using the specific 3.3V on the IC)

Looking at what is most likely the board that you use:
The AHT10 itself is specified for 1.8 - 3.6V, the ENS160 at 1.8V core supply and up to 3.6V DATA IO supply. The regulator of the board will limit the DATA IO supply to 3.3V, and switch to pass-thru mode at lower voltages. A second 1.8V regulator supplies the 1.8 V for the ENS160 core.
In any case the signal level at the I2C bus is 3.3V, even when the board us powered with 5V.

[robert-hh]

If the breakout modules you use have a 5V VCC input, and you need 5V anyhow for the LCD, then it's fine to use it. assuming that the I2C bis levels are at 3.3V. If breakout modules do not have a separate regulator, then 3.3V has to be used. The load at the PICO 3V3 pin should not exceed 300mA. Less, if the RP2040 drives other loads as well.

The maximum rating for a Pico GPIO pin specified in the data sheet is IOVDD + 0.5V. With 3.3V as IOVDD it amounts to 3.8V. I made a short test with an I2C interface to a LCD, operated at 5V and connected to a Pico. The 4.7k pull-up resistors of the interface force the GPIO levels to a high level of 3.95V, just above the Pico maximum rating. At the same time, 3.95V is above the high level H of 3.5V specified for the i2C interface. Therefore it works, even if is not good practice. It may not break the Pico, because the inrush current is limited by the pull-up resistor. Besides that, trouble may arise if more devices with with a different signal level are connected to the same bus. If they pull the high level on the bus below 3.5V, operation of the LCD's I2C interface is affected.