AstroPi Cube
Raspberry Pi is powered by a 5v coming from a 12v to 5v 3A transformer. These 3A are dedicated to the Raspberry Pi and are not powering any other equipment to avoid using energy that could be useful (USB ports, etc.). Another transformer is providing 5v 3A to the rest of the equipments (probes, sensors, GPS, etc.).
All GPIOs from the Raspberry Pi 4B are used. The one remaining unused (16/20/21) has been wired to modules, just in case they want to be used.
This module is used in order to convert our 12v input power into 5v (up to 3A) output power. The output will be used only by the Raspberry Pi. At first, I was using a home made circuit with L7805 and LM2576 MOSFETs. However, these circuits were close to 50% and 75% efficiency. I preferred to go with a MP2315 microchip circuit approaching 90% efficiency. Thus, less power is loss in heat, especially on battery mode. Buck Converter was choose according to this comparator.
This module is used in order to convert our 12v input power into 5v (up to 3A) output power. The output will be used by the rest of the 5v equipments (probes, fan, ammeters, etc.).
Although a very big part of the drawing, this part is very easy to understand because it's the same pattern repeating. On one side (left), different inputs are connected to the ACS712 microchip in serial, which is transforming the current (Amps) into a voltage (analog output). However, the Raspberry Pi is not able to understand analog inputs and only deals with digital inputs (1/0, LOW/HIGH, ON/OFF). Thus, we have to link our ACS712 to an Analog to Digital (ADC) converter in order to speak with the Raspberry Pi. This is provided by the MCP3008 microchips. Microchips are then connected to the Raspberry Pi using SPI bus (MOSI, MISO, etc.).
4 probes connections are available in order to read 4 temperatures and manage up to 4 dew heater straps. These probes are connected to the Raspberry Pi using the 1-Wire protocol. However, you will notice that unless they should have been connected on the same GPIO, they actually are on 4 different GPIO. Although it was possible to use just one, I wanted to be able to differentiate which probe was connected and on which GPIO. Thus, I'm able to send the right temperature / voltage to the right dew heater. This means that even if you don't plug the probes and dew heaters in the right order, the Raspberry will still know how to deal with it!
4 dew heaters are available and connected to the 4 dew temperature probes. Regarding the temperature and the operating mode defined in the web interface (AUTO / MANUAL / 100%), the Raspberry will send the correct power to the dew heaters in order to avoid dew formations on equipments.
One buzzer is available on the board and activated on some inputs only:
- High Raspberry Pi temperature detected [LONG BIP]
- Rain detected (using Meteo Module) [SHORTS BIPS]
- Save launched (using Meteo Module) [SHORT BIP on start / SHORT BIP on save]
One GPIO is dedicated to power OFF all circuit LED when Dark mode is activated.
Two GPIOs are dedicated to DSLR and can be remote controlled using the web interface: one for focus and the other one for shutter release. These are compatible with Nikons DSLR and maybe other (but untested).
Raspberry Pi 4B fan an can be also remote controlled a powered ON / OFF / AUTO using the web interface. Two transistors are used because we want the fan to be turned ON by default when Raspberry GPIO is OFF / LOW.
An accelerometer (optional) can be added to the board and remotely controlled. It can be used for example to stop DSLR taking picture when too many vibrations are detected.
GPS (optional) allows to receive GPS position and accurate time. This GPS is optional but strongly advised if none provided by another way.
Modules can be connected to the AstroPi project via the USB Type C ports. Theoretically, up to 127 equipments (127 different I2C addresses) can be connected within different modules, which should be sufficient for astrophotography and astronomy projects. Modules have to use the I2C protocol (see I2C related section in this Wiki) and can cohabit together. Three more Raspberry Pi GPIO are available to modules but cannot be used in same time bu modules. Finally, modules USB Type C provides 12v up to 3A power. Please be aware that equipments using 5v or 3v3 will need a buck converter before being connected.
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