The whole point of this blog originally was to use an Arduino and be able to monitor the engine status. Originally, I was going to use a Mega, and a bunch of shields. The old eco-system caused me to lean that way. Mega on the bottom, a custom shield next, and a Bluetooth shield on top. The world has moved on, and now I can use ESP-32 and 8266's with built in Wifi and Bluetooth. The boards only cost about $10, instead of the $20+ for the Mega and Bluetooth shield.
The sensors can mostly be wired to the ESP-8266 board with SPI (3 wire) communications, through adapter boards. If I need an analog or digital input, it is available on the board as well. There are very inexpensive thermocouple modules available, that would take care of the CHT and EGT measurements. The oil pressure and temperature would be analog inputs if I stick with the stock probes, but there is the Dallas18b20 probe that could be used to measure temperature, but there only one temperature measuring point on the engine. The Dallas 18B20 can be used for OAT measuring.
The oil pressure transducer is off on a flex pipe, with a manifold for to hold the hobbs switch. (theoretically, the oil pressure measurement could be combined in the computer somewhere to enable the hobbs timing measurements). There are nice solid state pressure sensors that may be appropriate for fuel and oil pressure, I need to do additional research.
Volt and Amp measurements can be done using the analog inputs, using the existing shunt for current measurements, or adding another shunt. There are also hall effect sensors that could be used to measure current. Using various current sensors would allow measuring all the important values at once, charge rate, drain rate, etc.
The tach measurement can come off the mag or EI unit. A transistor or optoisolator should work when connected to a pin that accepts interrupts.
Other sensors could be added or deleted anytime using additional nodes. If I want to measure the airflow through the baffles, I could add a node with multiple pitot tubes to see where the air might be leaking.
Then the question becomes, how many nodes should I use? It would be tempting to build one for each sensor, I want to limit the nodes to one function (I've said that before). How gray to I want that idea, one function could be all the thermocouples. Another node for all the oil information (pressure, temperature). Another for the fuel pressure, levels. Convenience may dictate some other arrangement, like thermocouples left side, thermocouples right side, that way the wires don't have to be so long.
Each node will still need 5V or 3V connected. It would be tempting to use the micro-USB connectors on the boards to feed the power. I think, the constant vibration would make the connectors fatigue very quickly, and the power would be falling out. It would probably be best to solder the power to the boards.
A $10 raspberry PI zero could be the NodeRed/MQTT hub. The raspberryPI should be mounted inside the cockpit. I am sure the WiFi signal can get around the firewall on a plastic airplane. Even a metal aircraft should have WiFi from the engine compartment to the cockpit. I'd have to try it out though.
In the cockpit, PLA printed enclosures should work fine. In the engine compartment, there may be problems with PLA or printed enclosures (constant vibration, heat, and rain). 3D printing my own enclosures may be compromised quickly. It may take some experimenting, certainly to make appropriate mounting choices, considering the sensor wiring stresses and heat.
NodeRed should allow nice cockpit displays of the instruments, and allow logging in various formats including CSV. Using the same CSV layout as the COTS instruments (like J.P Instruments) would allow people to analyze engine performance using off the shelf tools (excel, etc). The file could be scp'd from the Arduino, right to a tablet or phone, taken home and analyzed.
I don't know. I see a few worrying things, but nothing that is really scary about doing it. Can you talk me out of it?
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