i2cdetect in the read direction hangs/crashes after finding a sensor

[sp4ghet]

I'm using an Arduino Mega 2560 R3 with a MH-Z16 CO2 sensor in I2C mode

I basically just took the sample for I2Cdetect verbatim (just swapped the order of Read/Write)

#![no_std]
#![no_main]

use arduino_hal::{prelude::*, I2c};
use panic_halt as _;

const NDIR_ADDR: u8 = 0x4D;

#[arduino_hal::entry]
fn main() -> ! {
    let dp = arduino_hal::Peripherals::take().unwrap();
    let pins = arduino_hal::pins!(dp);

    let mut serial = arduino_hal::default_serial!(dp, pins, 57600);

    let mut led = pins.d13.into_output();
    let mut i2c = arduino_hal::I2c::new(
        dp.TWI,
        pins.d20.into_pull_up_input(),
        pins.d21.into_pull_up_input(),
        100000,
    );

    ufmt::uwriteln!(&mut serial, "Read direction test:\r").unwrap_infallible();
    i2c.i2cdetect(&mut serial, arduino_hal::i2c::Direction::Read)
        .unwrap_infallible();

    ufmt::uwriteln!(&mut serial, "Write direction test:\r").unwrap_infallible();
    i2c.i2cdetect(&mut serial, arduino_hal::i2c::Direction::Write)
        .unwrap_infallible();

    loop{};
}

/// serial output
Read direction test:
-    0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:       -- -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- 4d

It seems to run until it finds the sensor, and then it freezes.
the Write direction seems to run fine, but the read direction hangs.
I've tried adding some code below the i2cdetect but it doesn't appear as if any of it actually runs.

I've tried using the normal Arduino/C++ code provided by the manufacturer and it worked (connected and sent measurements over serial) so I don't think I've setup the hardware incorrectly, but please let me know if I fumbled something obvious.

I also tried just calling ping and it seemed to behave the same way (unsurprisingly..) where the ping goes through, but all following calls to i2c hang/panic(?)

    let pinged = i2c
         .ping_device(NDIR_ADDR, arduino_hal::i2c::Direction::Read)
         .unwrap();
    ufmt::uwriteln!(&mut serial, "Pinged: {}\r", if pinged { 1 } else { 0 }).unwrap();

    ufmt::uwriteln!(&mut serial, "Read direction test:\r").unwrap_infallible();
// this code doesn't run (except the first row of labels)
    i2c.i2cdetect(&mut serial, arduino_hal::i2c::Direction::Read)
        .unwrap_infallible();

[sp4ghet]

If it is necessary this is the product page (links to datasheets and sample code)

https://github.com/SandboxElectronics/NDIR/tree/master/NDIR_I2C

https://sandboxelectronics.com/?product=mh-z16-ndir-co2-sensor-with-i2cuart-5v3-3v-interface-for-arduinoraspeberry-pi

[stappersg]

My advice to sp4ghet:

• Close this issue
• cargo generate --git https://github.com/Rahix/avr-hal-template.git --name ndir_mvp
• Keep the mvp a minimum viable product, meaning: Stay away from swapping the order of Read/Write and other let me change this now, I will need it later away
• Check, double check and triple check the hardware setup. That implies having a schematic of the electronics. And above all: Understand all the hardware involved
• Document your prototype further. Do it for your future self and do it for your current self that is seeking help from others.
• Enjoy the challenge of getting to work what you envision
• Persist
• Smile humbly upon reaching your goal
• Maybe publish the achievement (It is 2025, there is something called Internet, every one is a publisher.)

My advice to everyone seeking help with their project:

• Understand the gist of http://www.catb.org/~esr/faqs/smart-questions.html
• Aim for win win