Sense Hat sensor wierdness. Ambient light is affecting humididty reading?

[alphanumeric]

I have a Sense Hat mounted to a Pi A+ setup as a weather clock. It displays the day, date, time, temp, humidity and barometric pressure in a continuously scrolling message on the LED matrix. Just recently the humidity started displaying negative values when I take it outside. I have another one in the house that never does this. I swapped sense hats between the two and it made no difference. The one in the house reads normal but my portable one reads negative values some times, when outside and the humidity is low. I redid the install with the latest Stretch and it didn't help.
My portable is in a waterproof enclosure, but I have drilled some vent holes in it so outside air can get in. And any hot air generated by the electronics can get out. I'm thinking I may have to add more holes or make them bigger maybe? The vent holes are small so rain and snow can't get on the electronics. I have a couple on each side and a few on the bottom. Build pictures are here, https://1drv.ms/f/s!AjOYwiwlwDtpgq8_0VrdS3_H5xL_AA
Power is supplied by a powerboost 1000c and LIPO battery. Temps did read high so I added a BMP180, mounted externally to read the ambient temps. I also have an Si1145 to read the UV and ambient light levels. I use the light levels to adjust the LED matrix brightness. Here is the code I'm using.

Code: Select all

import os
import time, datetime
import Adafruit_BMP.BMP085 as BMP085
import SI1145.SI1145 as SI1145
import RPi.GPIO as GPIO
from sense_hat import SenseHat, ACTION_PRESSED, ACTION_HELD, ACTION_RELEASED
   
sense = SenseHat()
sense.set_rotation(180)
sense.set_imu_config(False, False, False)
sense.low_light = False

bmp = BMP085.BMP085()
uvs = SI1145.SI1145()

GPIO.setmode(GPIO.BCM)  
GPIO.setwarnings(False)
GPIO.setup(5, GPIO.IN, pull_up_down = GPIO.PUD_OFF)  
GPIO.setup(16,GPIO.OUT, initial=1) #Red
GPIO.setup(19,GPIO.OUT, initial=1) #Yellow
GPIO.setup(20,GPIO.OUT, initial=1) #Green
GPIO.setup(21,GPIO.OUT, initial=1) #Blue


s=(0.1) # scroll speed
w=(0) # color all white toggle
o=(165)
L=(1) #LED's on or off
x=(2) #shutdown variable
m=(0)

def Shutdown(channel):  
    global x
    x = (0)

def readvis():
    vis = uvs.readVisible()
    global w
    global o
    global L
    global m
    if vis < 270 and m == (0):
        sense.low_light = True
        w = (0)
        o = (165)
        L = (1)
    elif vis >= 270 and vis < 500 and m == (0):
        sense.low_light = False
        w = (0)
        o = (165)
        L = (0)
    elif vis >= 500 and m == (0):
        sense.low_light = False
        w = (255)
        o = (255)
        L = (0)
    
# is really stick down
def pushed_up(event):
    global L
    global m
    if event.action == ACTION_PRESSED:
       sense.low_light = True
       L = (1)
       m = (1)
        
# is really stick up
def pushed_down(event):
    global L
    global m
    if event.action == ACTION_PRESSED:
       sense.low_light = False
       L = (0)
       m = (1)

#is really stick right
def pushed_left(event):
    global w
    global o
    global m
    if event.action == ACTION_PRESSED:
        w = (255)
        o = (255)
        m = (1)
        
# is really stick left
def pushed_right(event):
    global w
    global o
    global m
    if event.action == ACTION_PRESSED:
        w = (0)
        o = (165)
        m = (1)

def pushed_middle(event):
    global m
    if event.action == ACTION_PRESSED:
        m = (0)

sense.stick.direction_up = pushed_up
sense.stick.direction_down = pushed_down
sense.stick.direction_left = pushed_left
sense.stick.direction_right = pushed_right
sense.stick.direction_middle = pushed_middle

GPIO.add_event_detect(5, GPIO.FALLING, callback = Shutdown, bouncetime = 2000)

while True:

    readvis()

    dateString = "%A %B %-d %-I:%M %p"
    msg = "It is %s" % (datetime.datetime.now().strftime(dateString))
    sense.show_message(msg, scroll_speed=s, text_colour=(w, 255, 255))

    t = bmp.read_temperature()
    t = (round(t))
          
    if t <= 0: 
        tc = [w, w, 255]   # Blue
        GPIO.output(16, 1) # Red
        GPIO.output(19, 1) # Yellow
        GPIO.output(20, 1) # Green
        GPIO.output(21, L) # Blue <
    elif t > 0 and t < 13:
        tc = [255, 255, w] # Yellow
        GPIO.output(16, 1) # Red
        GPIO.output(19, L) # Yellow <
        GPIO.output(20, 1) # Green
        GPIO.output(21, 1) # Blue
    elif t >= 13 and t <= 25:
        tc = [w, 255, w]   # Green
        GPIO.output(16, 1) # Red
        GPIO.output(19, 1) # Yellow
        GPIO.output(20, L) # Green <
        GPIO.output(21, 1) # Blue
    else:
        tc = [255, w, w]   # Red
        GPIO.output(16, L) # Red <
        GPIO.output(19, 1) # Yellow
        GPIO.output(20, 1) # Green
        GPIO.output(21, 1) # Blue
        
    msg = "and %sc" % (t)
    sense.show_message(msg, scroll_speed=s, text_colour=tc)

    h = sense.get_humidity()
    h = (round(h))

    if h > 100:
        h = 100
    elif h >= 30 and h <= 60:
        hc = [w, 255, w]  # Green
        msg = "with %s%% Humidity" % (h)
        sense.show_message(msg, scroll_speed=s, text_colour=hc)
    elif h > 60 and h < 80:
        hc = [255, 255, w]  # Yellow
        msg = "with %s%% Humidity" % (h)
        sense.show_message(msg, scroll_speed=s, text_colour=hc)
    else:
        hc = [255, w, w]  # Red
        msg = "with %s%% Humidity" % (h)
        sense.show_message(msg, scroll_speed=s, text_colour=hc)

    readvis()

    ph = bmp.read_pressure()
    p = ph / 100
    p = round(p)
        
    if p > 0 and p < 985:
        pc = [255, w, w]  # Red
        msg = "- Barometer is Very Low @ %smb - Storm Watch" % (p)
        sense.show_message(msg, scroll_speed=s, text_colour=pc)
    elif p >= 985 and p < 1005:
        pc = [255, 255, w]  # Yellow
        msg = "- Barometer is Low @ %smb - Possible Percipitation" % (p)
        sense.show_message(msg, scroll_speed=s, text_colour=pc)
    elif p >= 1005 and p < 1025:
        pc = [w, 255, w]  # Green
        msg = "- Barometer is Mid Range @ %smb" % (p)
        sense.show_message(msg, scroll_speed=s, text_colour=pc)
    elif p >= 1025 and p < 1050:
        pc = [w, w, 255]  # Blue
        msg = "- Barometer is High @ %smb" % (p)
        sense.show_message(msg, scroll_speed=s, text_colour=pc)
    elif p >= 1050:
        pc = [255, w, w]  # Red
        msg = "- Barometer is Very High @ %smb - Expect Dry Conditions" % (p) 
        sense.show_message(msg, scroll_speed=s, text_colour=pc)

    uv = uvs.readUV()
    u = uv/100
    u = (round(u))

    if u > 0 and u < 3 and L == 0:
        msg = "- UV Index is Low @ %s" % (u)
        sense.show_message(msg, scroll_speed=s, text_colour=(w, 255, w)) # Green        
    elif u >= 3 and u < 6 and L == 0:
        msg = "- UV Index is Moderate @ %s" % (u)
        sense.show_message(msg, scroll_speed=s, text_colour=(255, 255, w)) # Yellow        
    elif u >= 6 and u < 8 and L == 0:
        msg = "- UV Index is High @ %s" % (u)
        sense.show_message(msg, scroll_speed=s, text_colour=(255, o, w)) # Orange       
    elif u >= 8 and u < 11 and L == 0:
        msg = "- UV Index is Very High @ %s" % (u)
        sense.show_message(msg, scroll_speed=s, text_colour=(255, w ,w)) # Red
    elif u >= 11 and L == 0:
        msg = "- UV Index is Extreme @ %s" % (u)
        sense.show_message(msg, scroll_speed=s, text_colour=(255, w, 255)) # Violet
        
    #vis = uvs.readVisible()

    #msg = "and the VIS is %s" % (vis)
    #sense.show_message(msg, scroll_speed=s, text_colour=(255, w, 255))

    if x == 0:
        sense.clear()
        os.system("sudo shutdown now -P")
        time.sleep(30)
    elif x == 1:
        sense.clear()
        raise SystemExit
        time.sleep(30)

# Last edited on April 12th 2018
# run sudo crontab -e
# add
# @reboot python3 /home/pi/THPU.py &

[alphanumeric]

Increasing the case ventilation didn't help. So what is the trick to getting the sense hat to read accurately? They are in a case on the space station, do they not work there?

[alphanumeric]

The plot thickens? I just redid my portable with an older Jessie backup image I had made, and swapped in my current python file. Still doing it. What I discovered though, is its the sunlight doing it? If I put it in direct sunlight the % humidity goes to 0%. Almost immediately so its not from the heat of the sun. I have it coded to just show 0 if its zero or below. Thinking I may have messed up my code for the light sensor some how and it was interacting, I took my indoor one out side for a test. It does the same thing? No light sensor ect on this one and no auto DIM etc. If I manually set it to full bright, and all white text, inside it reads the humidity OK. So its not my python code.
My inside weather clock is a Pi A+, DS3231 RTC on a Proto Hat and Sense Hat on top of that. No case, open air cooling.
My portable weather clock is the same as above but has a BMP180 temp sensor and Si1145 light sensor. The BMP180 is mounted externally on the bottom of the case, and the Si1145 is mounted externally on the top of the case. Both Sense hats have black diffusers mounted in front. The portable is in a weather proof case that has ventilation holes drilled in it. It's powered by a powerboost 1000c and LIPO battery.
I usually place the portable in the shade to make reading the LED matrix easier, and help get accurate temp readings. Because of a wet field at our dog park we have moved and its been out in the sun more. And that's when I noticed the weird readings. Here is the simpler code I use for my indoor unit.

Code: Select all

import os
import time, datetime
from sense_hat import SenseHat, ACTION_PRESSED, ACTION_HELD, ACTION_RELEASED
        
sense = SenseHat()
sense.set_rotation(180)
sense.set_imu_config(False, False, False)
sense.low_light = True

s=(0.065) # scroll speed
w=(0) # color all white toggle
x=(2) #shutdown variable

# is really stick down
def pushed_up(event):
    if event.action == ACTION_PRESSED:
       sense.low_light = True
        
# is really stick up
def pushed_down(event):
    if event.action == ACTION_PRESSED:
       sense.low_light = False

#is really stick right
def pushed_left(event):
    global w
    if event.action == ACTION_PRESSED:
        w = (255)
        
# is really stick left
def pushed_right(event):
    global w
    if event.action == ACTION_PRESSED:
        w = (0)

def pushed_middle(event):
    global x
    if event.action == ACTION_PRESSED:
        x = 0

sense.stick.direction_up = pushed_up
sense.stick.direction_down = pushed_down
sense.stick.direction_left = pushed_left
sense.stick.direction_right = pushed_right
sense.stick.direction_middle = pushed_middle

while True:

    dateString = "%A %B %-d %-I:%M:%p"
    msg = "It is %s" % (datetime.datetime.now().strftime(dateString))
    sense.show_message(msg, scroll_speed=s, text_colour=(w, 255, 255))

    t = sense.get_temperature()
    t = round(t)
          
    if t <= 0: 
        tc = [w, w, 255]  # Blue
    elif t > 0 and t < 13:
        tc = [255, 255, w]  # Yellow
    elif t >= 13 and t <= 25:
        tc = [w, 255, w]  # Green
    elif t > 25:
        tc = [255, w, w]  # Red                 
    msg = "and %sc" % (t)
    sense.show_message(msg, scroll_speed=s, text_colour=tc)

    h = sense.get_humidity()
    h = round(h)

    if h < 0:
        h = 0

    if h > 100:
        h = 100

    if h < 30:
        hc = [255, w, w]  # Red
        msg = "with %s%% Humidity" % (h)
        sense.show_message(msg, scroll_speed=s, text_colour=hc)
    elif h >= 30 and h <= 60:
        hc = [w, 255, w]  # Green
        msg = "with %s%% Humidity" % (h)
        sense.show_message(msg, scroll_speed=s, text_colour=hc)
    elif h > 60 and h < 80:
        hc = [255, 255, w]  # Yellow
        msg = "with %s%% Humidity" % (h)
        sense.show_message(msg, scroll_speed=s, text_colour=hc)
    elif h >= 80:
        hc = [255, w, w]  # Red
        msg = "with %s%% Humidity" % (h)
        sense.show_message(msg, scroll_speed=s, text_colour=hc)

    p = sense.get_pressure()
    p = round(p)
        
    if p > 0 and p < 985:
        pc = [255, w, w]  # Red
        msg = "- Barometer is Very Low @ %smb - Storm Watch" % (p)
        sense.show_message(msg, scroll_speed=s, text_colour=pc)
    elif p >= 985 and p < 1005:
        pc = [255, 255, w]  # Yellow
        msg = "- Barometer is Low @ %smb - Possible Percipitation" % (p)
        sense.show_message(msg, scroll_speed=s, text_colour=pc)
    elif p >= 1005 and p < 1025:
        pc = [w, 255, w]  # Green
        msg = "- Barometer is Mid Range @ %smb" % (p)
        sense.show_message(msg, scroll_speed=s, text_colour=pc)
    elif p >= 1025 and p < 1050:
        pc = [w, w, 255]  # Blue
        msg = "- Barometer is High @ %smb" % (p)
        sense.show_message(msg, scroll_speed=s, text_colour=pc)
    elif p >= 1050:
        pc = [255, w, w]  # Red
        msg = "- Barometer is Very High @ %smb - Expect Dry Conditions" % (p) 
        sense.show_message(msg, scroll_speed=s, text_colour=pc)
        
    if x == 0:
        sense.clear()
        os.system("sudo shutdown now -P")
        time.sleep(30)
    elif x == 1:
        sense.clear()
        raise SystemExit
        time.sleep(30)

I use the sense hat joystick to adjust the LED matrix screen brightness and do a shutdown. Stick up is bright, stick down is low light. Right changes the text to all white, left to colored text. Center push shuts down. I was doing this manually on my portable to make reading the LED matrix easier in bright light. Now I use the Si1145 to do it all manually.

[alphanumeric]

Ok, I had a friend check his Sense Hat and its doing the same thing? Ambient light shining on the sensor is causing the % humidity reading to immediately decrease. The brighter the light the more the reading goes negative. How is this even possible?

[alphanumeric]

I put a small piece of black packing foam over the sensor, and masked off the back part of the diffusor over the sensor. It appears to be reading normal now. Air is getting through the foam but the light isn't. It's giving me a reading and that's not changing when I move it from dark to light. The only gotcha may be if the foam retains any moisture in high humidity conditions. I'll likely figure something better out eventually, but it will do for now.

[alphanumeric]

No comment from Pi Foundation? Or anybody for that matter? I'm not making this stuff up guys.

[alphanumeric]

@ShiftPlusOne @jamesh Any comment? Just looking for some feedback?

[bensimmo]

I just used a small program with printing humidity and a sleep in a loop every half second
Shined and white led light tourch and no change. Just reading flickering between 56+-0.8, it not the most stable reading.


I can try brighter lights.
Putting a black SD card resting just above it doesn't alter it really. (We have bright led lighting in here).

[alphanumeric]

If you can, try bright sunlight, maybe its UV or non visible light? I'm going to go get a flashlight and see what that does for me. Thank's for the reply. This one really has me scratching my head.

[alphanumeric]

Shining a flashlight on the humidity sensor is lowering the reading for me. Went from 60% to 30%. Flashlight needs a new battery. My Sense hat shows as version 1.0 if that matters. And has (c) Raspberry Pi 2015 silk screened on it.

[alphanumeric]

Hmm, this is interesting. Shining my LED flashlight on it does noting, but shining my older flashlight with an incandescent bulb in it lowers the reading.

[alphanumeric]

It appears white LED's are Blue LED's with extra phosphor.

[6by9]

Those who really worked on the Sense Hat aren't around at the moment.
Scuttlebutt says there were a batch with dodgy sensors that were returning negative values, but unsure on details.

Are these Sense HATs that have been behaving and now don't, or have you never had it in this environment before so you don't know whether it has always been a problem?

[bensimmo]

I've had some lamps out today
UV led (so 390/400nm) no effect.
deeper UV, I forget where but 300-340nm ish, nothing.

Green laser, no effect
Red laser, if directly over the hole (silver bit) then I can get it to temporarily trigger a drop to 30 (it was hovering around 50), and it recovers the next reading (read every half second).
The green laser after a bit, working out where the sensitive bit was above, would donate temp drop every now and again.

I have not CFLs to test with and cannot find my bright IRs.

CFL work similar to the White LED with the phosphor, so you ahve a blue and yellow emmision, hence white.
(only some newer led use RGB arrays for a tunable white).


So the laser is probably exciting something in the chip sensor briefly.

[alphanumeric]

Those who really worked on the Sense Hat aren't around at the moment.
Scuttlebutt says there were a batch with dodgy sensors that were returning negative values, but unsure on details.

Are these Sense HATs that have been behaving and now don't, or have you never had it in this environment before so you don't know whether it has always been a problem?

The one I first noticed it on is a portable I take with me to our dog park. Because the LED matrix is hard to see / read in bright sunlight I usually have it in the shade with the sun behind it. I had a suspicion the % humidity was reading lower than it should but didn't know why. I suspected it may be heat build up in the case. Its a waterproof case with a clear front. I had drilled some vent holes in it, and drilled some more when I noticed this happening. It didn't make any difference.
The end of the field we usually use got flooded and we moved location. No shade and the sun was shining directly on the front of my case. One very clear bright day I noticed the negative reading. This same sense hat has in the past read over 100%. Then I did some testing to try and figure out what was going on. I took both of mine outside and they both did the same thing. In the shade they read normal, or close to it. In the bright sun the reading immediately drop. It was +6 c at the time. I changed my code so it only ever shows as low as 0 and won't show anything above 100.
Both sense hats I've had for a while now and both are version 1.0. And both have black diffusors mounted in front covering the LED matrix and the sensors. Build pictures are here, https://1drv.ms/f/s!AjOYwiwlwDtpgq8_0VrdS3_H5xL_AA

EDIT: Just put some new pictures up showing the vent holes, and the other indoor weather clock.

[alphanumeric]

I've had some lamps out today
UV led (so 390/400nm) no effect.
deeper UV, I forget where but 300-340nm ish, nothing.

Green laser, no effect
Red laser, if directly over the hole (silver bit) then I can get it to temporarily trigger a drop to 30 (it was hovering around 50), and it recovers the next reading (read every half second).
The green laser after a bit, working out where the sensitive bit was above, would donate temp drop every now and again.

I have not CFLs to test with and cannot find my bright IRs.

CFL work similar to the White LED with the phosphor, so you ahve a blue and yellow emmision, hence white.
(only some newer led use RGB arrays for a tunable white).


So the laser is probably exciting something in the chip sensor briefly.

How old or new is your sense hat? What is the version number printed on the circuit board? Not sure if it matters but curious to know?

Now that I have the sensor covered up with black foam, and masked off the diffusor, it appears to be working normally. I don't have anything to compare it with, but sunlight isn't changing what its displaying.
I have a BME680 on the way that I'm going to hook up. I'll see if I can display both, one after the other and compare. The BME680 will be mounted externally on the bottom of my case facing down.

[bensimmo]

Near the time of the original SenseHAT, I don't think the version and changed anyway. For a start that would cause problems with AstroPi challenges.


So over two years old.

[alphanumeric]

Near the time of the original SenseHAT, I don't think the version and changed anyway. For a start that would cause problems with AstroPi challenges.


So over two years old.

Ok, thanks, I wasn't sure if there was more than one version. One of my A+'s is the older one with 256 MB of Ram and one is the newer V1.1 with 512 MB of Ram. That's why I asked. Thanks for the feedback and testing.

[ShiftPlusOne]

Are any of the affected Sense HATs new(ish)? Or are they all from around the time that they came out? I suspect it's a hardware issue with the sensor that shouldn't affect newer boards.

[alphanumeric]

Are any of the affected Sense HATs new(ish)? Or are they all from around the time that they came out? I suspect it's a hardware issue with the sensor that shouldn't affect newer boards.

No both are older ones bought around the time the sense hat was first released.

EDIT: They both have 2015 silkscreened on them, if that's any kind of indicator?

[alphanumeric]

went back and checked my order history and one was bought Dec 2015 and the other Jan 2017. One is newer than I thought it was.

[alphanumeric]

Added a BME680 and I'm now using it for the temperature, humidity and barometric pressure readings. The BME680 doesn't have the same aversion to light so all is good now. The only thing I'm using on the sense hat now is the LED matrix, so I think my next mod is to replace that with a Unicorn Hat HD for a bigger crisper display. Then repurpose the sense hat for another project. Might even give it to the grand kids to play with. It's still a nice bit of kit for learning etc. It's not going to waist that's for sure.