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Using an R-Pi 3 in the AstroPi (Confirmed Observation)

Mon Oct 23, 2017 6:04 pm

I read somewhere that the R-Pi 2 and R-Pi 3 are not used because of the heat they generate, they would not pass ESA standards for operating temperature. In reading this, I have set in my mind that the heat generated by these R-Pi units would interfere with the Sense_Hat sensors.

After building my AstroPi unit (3D Printed Plastic Case), i wanted to use one of my R-Pi 2 units but could not find one as the two I have are in separate projects. So I decided to use a spare R-Pi 3 unit I have. To keep things cool on the R-Pi 3, it has heat sinks on the CPU and I/O Chips. Assembling the AstroPi, it works great.

It works great until I did a modified scrolling_env.py program to sense the environment around it. Temperatures in NYC this past month while I made this AstroPi was in the low to mid 70s Fahrenheit. So I thought that it should be registering that as its temp. Instead it measured 85+ degrees. I ran the program a couple more times, and the temperature kept getting higher and higher. The highest temperature reading was 104.2 Fahrenheit.

I'm thinking to my self, "What's going on?"

Took the Astro Pi apart, and it was warm inside. The R-Pi 3 was hot but not burning hot, as the heatsinks were doing their job. Only thing I can figure out is that the R-Pi 3 issue with generating heat is interfering with the Sense_Hat's Thermometer. Did a few tests (like running the AstroPi Unit with its case open), and it confirms it - the heat created by the R-Pi 3 is interfering with the Sense_Hat's thermometer. It is also interfering with the humidity and barometric sensors as well but not as great as the thermometer.

Now to get a R-Pi Model B+ to replace the R-Pi 3 and see if this would works as it should.

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Re: Using an R-Pi 3 in the AstroPi (Confirmed Observation)

Tue Oct 24, 2017 11:30 am

Ah yes, this is a known issue.

Even with the old Pi 1 B+ there is some thermal leak from the CPU into the temperature sensors, we've even seen student experiments (which were run on board the ISS) where the they attempted to calibrate out the thermal leak. Have a look here for an example.

It's actually a design flaw with the Sense HAT, the top and bottom fill of the PCB should have been pulled back around the sensor packages to mitigate heat leaking into the sensors. But because we were making the boards in a hurry, due to Tim Peake's launch schedule, we made a mistake with it. Consequently, because the units that went to space have the fault, we thought everyone else needs to get the fault too. Mainly so everyone gets the exact same thing which is on the ISS.

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Re: Using an R-Pi 3 in the AstroPi (Confirmed Observation)

Tue Oct 24, 2017 6:04 pm

Given that you have a plastic case that doesn’t need to meet ESA specs, it might be plausible to stick a small fan in there. Mmm, and some extra holes of course.

Or you could get a machined aluminium case from us (www.astropicase.com); my demo unit has always had a Pi3 in it and seems to be happy. Even the wifi works, despite the metal cage.
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Re: Using an R-Pi 3 in the AstroPi (Confirmed Observation)

Tue Oct 24, 2017 8:25 pm

timrowledge, I would love a machined metal case but being a retired teacher in the USA forces me to live on a limited income. I think it is a great product, I just can not afford it.

I am trying to start a R-Pi program here in the states in New York City, NY., and hope to have it up and running by 2018. Part of it will include robots controlled by Astro Pies.

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Re: Using an R-Pi 3 in the AstroPi (Confirmed Observation)

Fri Nov 10, 2017 1:18 pm

I have one setup that is a Pi A+ > Proto Hat with RTC > Sense Hat. Without a case that Sense Hat keeps pretty accurate temps. The Proto Hat with a tall stacking header puts enough space between the Pi and Sense Hat and provides a bit of a barrier between the two.
Proto Hat https://www.adafruit.com/product/2310
stacking header https://www.adafruit.com/product/1979
DS3231 breakout board https://www.adafruit.com/product/3013
I have an identical portable setup in a ventilated case and over time the Sense Hat temps read high. No cooling fan but lots of ventilation holes were drilled in the case, top, bottom and sides. I ended up mounting a BMP180 temp sensor on the exterior of the case to get accurate readings. That case also has a large LIPO battery with a powerboost 1000c battery charger and voltage booster inside. I think it was accounting for a lot of the heat in the case.

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