Here is a list of the posts in this challenge
Gr0G - 03 - High-pressure system design
Gr0G - 07 - Playing with the Gertbot
Gr0G - 11 - Building the box (2)
Gr0G - 12 - Building the high-pressure system
Gr0G - 13 - Building the high-pressure system (2)
Source code available at https://github.com/ambrogio-galbusera/gr0g, https://github.com/ambrogio-galbusera/gr0g-ble-android and https://github.com/ambrogio-galbusera/gr0g-ble
An update about the Gr0G box
Today I installed some components, namely the dehumidifier, the fan, the keypad and the control board
The dehumidifier
The dehumidifier is built around a Peltier cell. The concept behind the dehumidifier is very simple: damp air is pulled over the front of a cold heat sink. As the air passes over the cold surface, it condenses
I have a TEC1-12706 Peltier cell in my lab. These universal IDs clearly indicate the size, number of stages, number of couples, and current rating in amps, as seen in the adjacent diagram
The vast majority of thermoelectric coolers have an ID printed on the cooled side, but, to stay on the safe side, I connected the cell to the power supply for 30 seconds and, with my finger, I checked where the hot and cold side were
I used some heat sink I took off from old PCs.
The bigger heat sink will be placed on the "hot" side of the cell to dissipate the heat as fast as possible. A Peltier cell creates a temperature gradient between the two faces, so the colder is the hot side, the colder is the cold side
The smaller heat sink will be in touch with the "cold" side.
I also added an extra fan on the cold side, to force air against the cold heat sink
Then I installed the control board, the keypad, the fan and the dehumidifier on the Plexiglas panel. While I was thinking of the best placement for these components, I realized that I never asked to myself a very fundamental question: how hot air behaves in microgravity? Air in microgravity has no weight, so convective movements due to difference in air density that we see on our planet no longer applies. This leads to some interesting effects. For example, the candle flame in microgravity is spherical because the hot air does not move upwards (https://science.nasa.gov/science-news/science-at-nasa/2013/18jun_strangeflames)
The absence of convective movements affects also astronauts sleep. When we sleep, we exhale hot gases (I mean, hotter than the external air). Hotter gases are less dense and naturally moves away from our head. In microgravity, the same gases will stagnate around our head. As we exhalate carbon dioxide, this may result in hypoxia. For this reason, astronauts have a fan in their sleep bed
That's said, it's not important that the fan is placed at the top of the Gr0G box: it can be installed in any position because hot air flows all around, not just upwards.
This it the final result
1. 4-keys keypad
2. Pimoroni Automation hat
3. Cooler
4. Dehumidifier
5. Pimoroni Enviro hat
6. Raspberry Pi (the Gertbot in not mounted in this picture)
The Pimoroni Enviro hat is mounted on a bracket so to measure environment parameters near the center of the cube, This to have the most precise value as possible. The bracket is made of harmonic steel. The sensor board is kept in place by two screws and bolts with rubber supports typically used to install servo motors (however some other mounting options should be evaluated, because the current one is not very solid) . The bracket is then connected to the plywood board with all the electronics by means of an electric terminal: this makes very easy to adjust the position of the sensor
I already developed some code (still to be improved and, yes, the that awful flicker has definitely to be removed)
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