jklondon
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Re: Astro Pi Temperature Sensor Reading

Sun Jan 10, 2016 10:27 pm

I brought the sensehat for a project I want to undertake using led grid but was hoping to get reliable temp readings for something else, clearly not going to happen it seems?

mattoni
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Re: Astro Pi Temperature Sensor Reading

Sun Jan 17, 2016 10:37 am

timrowledge wrote:It's not an option for the ISS use case but for home use you can connect the astropi via a 40-way ribbon cable and a male-male adaptor. I'll add a photo of my setup when I get to the office.
OK - picture -
The attachment IMG_0161.jpg is no longer available
I'm actually using a 40pin stacker header that passes through the astropi sockets and the cable can just plug on the top. Very convenient.
I'm trying to use your same setup but without success (it seems).
A male-to-male pin adapter and a 40 pin ide cable.
When i turn on the raspy, the led matrix has very low brightness and it remains on even after the boot.
(In normal condition the led matrix goes off after a while).
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jklondon
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Re: Astro Pi Temperature Sensor Reading

Sun Jan 17, 2016 12:28 pm

Cable connected right way round (try flipping) - keen to know if this works and want to do a similar setup

mattoni
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Re: Astro Pi Temperature Sensor Reading

Sun Jan 17, 2016 12:33 pm

The cable is connected the right way...

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experix
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Re: Astro Pi Temperature Sensor Reading

Sun Jan 17, 2016 7:14 pm

Could it be improved by attaching a good heat conductor or heat pipe to the sensor?

mattoni
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Re: Astro Pi Temperature Sensor Reading

Sun Jan 17, 2016 8:35 pm

experix wrote:Could it be improved by attaching a good heat conductor or heat pipe to the sensor?
Sorry experix, but i don't understand the purpose of an heat pipe over the sensor

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experix
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Re: Astro Pi Temperature Sensor Reading

Mon Jan 18, 2016 4:38 pm

The heat pipe would keep the sensor temperature much closer to the temperature at the other end of the pipe, minimizing the effect of warm components near the sensor. It's the same principle as the heat pipe you find attached to the CPU in a laptop, except that one is about removing heat produced by the CPU. A CPU heat pipe would probably be a terribly clumsy solution. I'm thinking of something much smaller-- don't know if such things are available, but you could probably make something. Maybe it doesn't even have to be a pipe; just a short piece of thick copper wire.

mattoni
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Re: Astro Pi Temperature Sensor Reading

Mon Jan 18, 2016 6:59 pm

experix wrote:The heat pipe would keep the sensor temperature much closer to the temperature at the other end of the pipe, minimizing the effect of warm components near the sensor. It's the same principle as the heat pipe you find attached to the CPU in a laptop, except that one is about removing heat produced by the CPU. A CPU heat pipe would probably be a terribly clumsy solution. I'm thinking of something much smaller-- don't know if such things are available, but you could probably make something. Maybe it doesn't even have to be a pipe; just a short piece of thick copper wire.
I'm not that an expert in heat transmission, but i think that in this case the only solution for reading right values of temperature is to keep the sensor (and so the sense hat) far from the pi cpu...not meters but some centimeter would be enough.
That's why i'm trying the flat cable solution.
Besides, with pi and sense hat on top of it, there is very few room for manuvre

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dobra-dobra
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Re: Astro Pi Temperature Sensor Reading

Tue Jan 19, 2016 4:07 am

mattoni wrote:
experix wrote:I'm not that an expert in heat transmission, but i think that in this case the only solution for reading right values of temperature is to keep the sensor (and so the sense hat) far from the pi cpu...not meters but some centimeter would be enough.
You can still have some heat from LED matrix if in use. There is no easy solution to this problem, but I will be more than happy to play with it as I like such challenges.

By the way, I compared humidity results obtained using Sense HAT with both DHT11 and DHT22 sensors and they also seem off quite a bit.

jklondon
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Re: Astro Pi Temperature Sensor Reading

Wed Jan 20, 2016 5:10 pm

mattoni wrote:
timrowledge wrote:It's not an option for the ISS use case but for home use you can connect the astropi via a 40-way ribbon cable and a male-male adaptor. I'll add a photo of my setup when I get to the office.
OK - picture -
IMG_0161.jpg
I'm actually using a 40pin stacker header that passes through the astropi sockets and the cable can just plug on the top. Very convenient.
I'm trying to use your same setup but without success (it seems).
A male-to-male pin adapter and a 40 pin ide cable.
When i turn on the raspy, the led matrix has very low brightness and it remains on even after the boot.
(In normal condition the led matrix goes off after a while).
Have exactly same led issue - using blackhat hack3r - any ideas?

alphanumeric
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Re: Astro Pi Temperature Sensor Reading

Mon Jan 25, 2016 5:58 pm

I used a tall stacking header https://www.adafruit.com/products/1979 and put it between my Pi and sense hat. I soldered a proto board to it https://www.adafruit.com/products/2310 Now my temps read ambient. I now also have a spot to mount my RTC module and a few other odds and ends with easy access to the GPIO pins.

alphanumeric
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Re: Astro Pi Temperature Sensor Reading

Mon Jan 25, 2016 6:03 pm

jklondon wrote:
mattoni wrote:
timrowledge wrote:It's not an option for the ISS use case but for home use you can connect the astropi via a 40-way ribbon cable and a male-male adaptor. I'll add a photo of my setup when I get to the office.
OK - picture -
IMG_0161.jpg
I'm actually using a 40pin stacker header that passes through the astropi sockets and the cable can just plug on the top. Very convenient.
I'm trying to use your same setup but without success (it seems).
A male-to-male pin adapter and a 40 pin ide cable.
When i turn on the raspy, the led matrix has very low brightness and it remains on even after the boot.
(In normal condition the led matrix goes off after a while).
Have exactly same led issue - using blackhat hack3r - any ideas?
I had my sense hat mounted on a Black Hat hacke3r Mini Kit and it worked without issue? Raspberry Pi A+. Raspbian Jessie. If your running Wheezy, the matrix will light up and just stay on until you do some updates and the sense hat support files.

EDIT: Are you sure you didn't get the ribbon cable backwards at one end? The ribbon cable goes over the top of the Pi, the opposite direction from the way it goes if your using a cobbler.
https://www.adafruit.com/products/2339
https://www.adafruit.com/products/2028

bensimmo
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Re: Astro Pi Temperature Sensor Reading

Thu Jan 28, 2016 4:54 pm

Having of course the same problem I tried the ribbon cable and doesn't really help much.

I found if I use a 1Wire DS18B20 as well, it much better and takes little room on top or even using the longer probe style.

For a few quid for 5 of them it may make your calibration better. (Given you can read from all 5 ds18 temp sensors at once)

mattoni
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Re: Astro Pi Temperature Sensor Reading

Sat Feb 13, 2016 7:51 am

alphanumeric wrote:I used a tall stacking header https://www.adafruit.com/products/1979 and put it between my Pi and sense hat. I soldered a proto board to it https://www.adafruit.com/products/2310 Now my temps read ambient. I now also have a spot to mount my RTC module and a few other odds and ends with easy access to the GPIO pins.
Can you post a picture of your solution?
Thanks

mattoni
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Re: Astro Pi Temperature Sensor Reading

Sat Feb 13, 2016 7:58 am

had my sense hat mounted on a Black Hat hacke3r Mini Kit and it worked without issue? Raspberry Pi A+. Raspbian Jessie. If your running Wheezy, the matrix will light up and just stay on until you do some updates and the sense hat support files.

EDIT: Are you sure you didn't get the ribbon cable backwards at one end? The ribbon cable goes over the top of the Pi, the opposite direction from the way it goes if your using a cobbler.
https://www.adafruit.com/products/2339
https://www.adafruit.com/products/2028
No, it's not an operating system version issue,
because with the sense hat direct on top of pi,
led matrix works fine.
And the cable is used the correct way :(

alphanumeric
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Re: Astro Pi Temperature Sensor Reading

Sat Feb 13, 2016 10:50 am

mattoni wrote:
alphanumeric wrote:I used a tall stacking header https://www.adafruit.com/products/1979 and put it between my Pi and sense hat. I soldered a proto board to it https://www.adafruit.com/products/2310 Now my temps read ambient. I now also have a spot to mount my RTC module and a few other odds and ends with easy access to the GPIO pins.
Can you post a picture of your solution?
Thanks
Here you go, https://onedrive.live.com/redir?resid=6 ... lder%2cjpg It's my public OneDrive folder. There are a couple of pictures and a video.

alphanumeric
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Re: Astro Pi Temperature Sensor Reading

Sat Feb 13, 2016 11:13 am

mattoni wrote:
had my sense hat mounted on a Black Hat hacke3r Mini Kit and it worked without issue? Raspberry Pi A+. Raspbian Jessie. If your running Wheezy, the matrix will light up and just stay on until you do some updates and the sense hat support files.

EDIT: Are you sure you didn't get the ribbon cable backwards at one end? The ribbon cable goes over the top of the Pi, the opposite direction from the way it goes if your using a cobbler.
https://www.adafruit.com/products/2339
https://www.adafruit.com/products/2028
No, it's not an operating system version issue,
because with the sense hat direct on top of pi,
led matrix works fine.
And the cable is used the correct way :(
OK, just wanted to make sure you didn't get the ribbon cable on backwards at one end. Even if the stripe for pin 1 is on the correct side, you can still get it wrong if you plug the cable into the wrong side of the board. From the top versus from underneath. Put it on the wrong way and pin 1 or the ribbon cable ends up on pin 2 or the sense hat. This is possible if your plugging in a double sided pin header. On the Pi looking down with the SD card slot on the left it goes.
246
137
On the sense hat looking down with the LED matrix on the left its the same.
Flip it over though and its
137
246
I think it needs to be plugged in from the top for pin 1 to match up with pin 1.. I had mine connected on my mini black hat kit and it worked fine.

xpire
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Re: Astro Pi Temperature Sensor Reading

Thu Feb 18, 2016 10:04 am

I am running the Sense Hat on Pi2. It is stacked directly on top of pi2.
I have an electronic thermometer and humidity placed next to it for comparison.
The HAT's temperature and humidity readings are way wrong!

I bought an angular header from adafruit (something like this https://www.adafruit.com/products/2823) to put between the Pi 2 and Sense Hat, so that the HAT is now perpendicular to the Pi 2 board and far way from the hot cpu. In theory, it is off the influence of CPU but still the HAT temperature is higher than actual by about 3.5C.
HAT temp: 24.5 ; Actual 20.9
HAT Hum: 63.9%; Actual 63

Then, I put an USB electrical fan to blow at the HAT so that the surrounding air is always replacing the warm air around the HAT and it is thus measuring the temperature of the surrounding air.

HAT Temp= 23.9 Hum=64.4 Actual Temp: 23.4 Humid: 53
HAT Temp= 22.6 Hum=72.8 Actual Temp: 22.1 Humid: 60
the temp. difference is down to 0.5C and Humid difference increased to about 12

It shows that the hot temperature from the SENSE HAT itself is affecting the accuracy even without the Pi 2 CPU near by.

It seems a FAN is a must for accurate temperature reading of HAT :cry:

Dennis

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Davespice
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Re: Astro Pi Temperature Sensor Reading

Thu Feb 18, 2016 8:11 pm

Hi folks

Just wanted to chime in here. This is a known issue with the Sense HAT, there is thermal conduction from the Pi 2 CPU through the PCB top and bottom fill to the humidity and pressure sensors (which also give you temp). We should have pulled back the fill around these sensors to avoid this but a mistake was made because we were designing it under the time constraints of the ESA flight safety schedule for Tim's launch. More info here: http://rpf.io/ap5

The problem is not so bad on a B+ which produces less heat. On the Astro Pi flight unit the Sense HAT sits above a middle board which houses the RTC and push button contacts. So it's not even noticeable there. You may be interested to know that one of the students that won Astro Pi, who's code is now on the ISS, wrote code to compensate for this temperature discrepancy using the relationship of the Pi CPU temperature to ambient. Check it out here.

You might find the problem is mitigated by increasing the distance of the Sense HAT away from the Pi 2 CPU, or by putting some kind of thermally conductive material in between to conduct the heat away from the Sense HAT. You might also find that it's not as bad if you have the Pi upside down, so that convection doesn't make the heat rise up to the Sense HAT.

I hope this helps.

xpire
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Re: Astro Pi Temperature Sensor Reading

Fri Feb 19, 2016 1:34 am

If what you said is true, how do you explain the temperature inaccuracy even after I have the Sense HAT perpendicular to the Pi 2 board. I even put a piece of paper on top of the Pi 2 to block any vertical warm air rising from the Pi 2 from reaching HAT. The Sense HAT is now vertical and should be free from any influence of the Pi 2 heat.

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Re: Astro Pi Temperature Sensor Reading

Fri Feb 19, 2016 12:00 pm

That may be due to the properties and accuracy of the sensors, I know the pressure sensor's temp reading is much less accurate.
I'll link the data sheets and you can take a look;

Pressure ST LPS25H
Humidity ST HTS221

mattoni
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Re: Astro Pi Temperature Sensor Reading

Thu Feb 25, 2016 7:03 am

alphanumeric wrote:
mattoni wrote:
alphanumeric wrote:I used a tall stacking header https://www.adafruit.com/products/1979 and put it between my Pi and sense hat. I soldered a proto board to it https://www.adafruit.com/products/2310 Now my temps read ambient. I now also have a spot to mount my RTC module and a few other odds and ends with easy access to the GPIO pins.
Can you post a picture of your solution?
Thanks
Here you go, https://onedrive.live.com/redir?resid=6 ... lder%2cjpg It's my public OneDrive folder. There are a couple of pictures and a video.
Oh that's really kind of you. Thank you for the pictures.
So you are using tha adafruit hat just for isolating the pi from the sense hat..

alphanumeric
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Re: Astro Pi Temperature Sensor Reading

Thu Feb 25, 2016 11:23 am

Right now its just a spacer to put some distance between the two. Eventually I'm going to add a Real Time Clock and it will be soldered to the proto board. I'll probably wire some switches to the GPIO via the proto board too.

BerlinRF
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Re: Astro Pi Temperature Sensor Reading

Sat Mar 05, 2016 1:39 pm

It's interesting and the first time I found a post about a problem I have from the first day on. The Sense Hat on a RPi2 shows a much higher temperature (~30 degrees Celsius in rooms for me) which does make it useless for serious termometer-applications, unfortunately. I always thought about an "design problem" but also considered my unit to be defect, because nobody else posted about this issue. I bought myself some placeholders (2 times "12MM 40Pin Female Stacking Header For Raspberry Pi 2") but as I just see, it reduces the problem but does not avoid it totally (now 26 degrees instead of real 21 degrees).
Thats really disappointing because it disallows to use the Hat in the compact manner it was designed for.
I also do not believe that it can be corrected because the offset (caused due to the heating of the RPi board) is not a linear function ...

alphanumeric
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Re: Astro Pi Temperature Sensor Reading

Sat Mar 05, 2016 2:08 pm

BerlinRF wrote:It's interesting and the first time I found a post about a problem I have from the first day on. The Sense Hat on a RPi2 shows a much higher temperature (~30 degrees Celsius in rooms for me) which does make it useless for serious termometer-applications, unfortunately. I always thought about an "design problem" but also considered my unit to be defect, because nobody else posted about this issue. I bought myself some placeholders (2 times "12MM 40Pin Female Stacking Header For Raspberry Pi 2") but as I just see, it reduces the problem but does not avoid it totally (now 26 degrees instead of real 21 degrees).
Thats really disappointing because it disallows to use the Hat in the compact manner it was designed for.
I also do not believe that it can be corrected because the offset (caused due to the heating of the RPi board) is not a linear function ...
I have a circuit board (proto board) mounted to my stacking header. It acts like a bit of a heat shield. If all you have is a stacking header to increase the space, but the space is all open. The heat will still eventually get there. Especially if you Pi is laying flat with the sense hat right above it. I have mine standing vertical so I can read the LED matrix. I flipped the display 180 degrees so the GPIO header is now on the bottom. This lets the heat escape out the top easier. There is a link to pictures in an earlier post I made in this thread. My temp reading is pretty close to ambient. If it's off its only a half a degree or so high. According to my thermostat anyway, and assuming its acurate.

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