Plasma2040 and ltr-559

Support
1

It’s a bit maddening to see the ltr-559 sensor linked from the plasma2040 sales page but not have any working code. This code /should/ work, as I can import the ltr559 library into Thonny:

import time
import plasma
from plasma import plasma2040
from ltr559 import LTR559

sensor = LTR559()

try:
    while True:
        sensor.update_sensor()
        lux  = sensor.get_lux()
        prox = sensor.get_proximity()

        print("Lux: {:06.2f}, Proximity: {:04d}".format(lux, prox))

        time.sleep(0.05)
except KeyboardInterrupt:
    pass

But it doesn’t. I get this error:
MPY: soft reboot
Traceback (most recent call last):
File “”, line 10, in
File “/lib/ltr559/init.py”, line 213, in init
File “/lib/i2cdevice/init.py”, line 165, in init
File “/lib/smbus2/init.py”, line 23, in
File “/lib/smbus2/smbus2.py”, line 25, in
ImportError: no module named ‘fcntl’

which seems to be a dead end.

It feels like pimoroni wants us to use this sensor with the plasma2040, but I’m at my wits end here. Thanks for any help you can provide.

2

Found myself a clue, which lets me make readings.

import time
from plasma import plasma2040
from pimoroni_i2c import PimoroniI2C
from breakout_ltr559 import BreakoutLTR559

i2c = PimoroniI2C(plasma2040.SDA, plasma2040.SCL)

sensor = BreakoutLTR559(i2c)

try:
    while True:
        reading = sensor.get_reading()
        lux = reading[BreakoutLTR559.LUX]
        prox = reading[BreakoutLTR559.PROXIMITY]
        print("Lux:", lux, "Prox:", prox)

        time.sleep(0.05)
except KeyboardInterrupt:
    pass

This code works if and only if I print out the variable “reading” in its entirety. If I try to access any of "reading"s components using the subscript in the example above, I get the error

Traceback (most recent call last):
  File "<stdin>", line 14, in <module>
TypeError: 'NoneType' object isn't subscriptable

If I run the same code in the Thonny command line, it works just fine.

What’s the difference between running the code in the command line versus a program?

3

Yeah, you have to setup i2c to read the sensor.
I use an LTR-559 for auto brightness on my Interstate 75 W.
To get just the Lux, and ignore the Proximity I use the following.

reading = ltr.get_reading()
lux = reading[BreakoutLTR559.LUX]
1 Like
4

I figured out the problem-- sometimes the sensor returns “None”, so I need to check if the variable “reading” is non-null first.

    ltr_reading = ltr.get_reading()
    if ltr_reading:
        lux = ltr_reading[ltr.LUX]
        if lux < 5:
            for i in range(NUM_LEDS):
                hue = float(i) / NUM_LEDS / 10
                led_strip.set_hsv(i, hue + offset, 1.0, BRIGHTNESS)
            led.set_rgb(10*speed, 0, 255 - 10*speed)
        else:
            for i in range(NUM_LEDS):
                led_strip.set_hsv(i, 0, 0, 0)
            led.set_rgb(0, 0, 0)

All better now!

1 Like
5

Nice, I may give that a go on my Plasma setup. I tried to do something similar with a BH1745. That stalled and I never got back to it. I wanted to auto adjust the color and intensity. Right now I set the color with the buttons on an Encoder Wheel. Then adjust the brightness with the wheel (rotating ring).
Want to use a BH1745 for Ambient Lighting - Support - Pimoroni Buccaneers