MPU9250 with ESP8266

[skipper@sy-barranas]

I noticed that the wifi module ESP8266 was used by some members of the forum. But not together with the MPU9250. That says at least my search.
I came up with this idea because I think about two connected Raspis. The first is to house the main server with external connections such as wifi, mqtt (iot), gms and connect additional sensors (temp, motor, tank, ...). The second should mainly / only manage the MPU (may be some other sensors). I wonder if it really is neccessary to use a grownup Raspi in this location.

1. If two OPs are involved. How are the calibrated compass values, for examlpe via SignalK, distributed to the second server? (MPU - server - server case)

The idea behind this is also to have a backup if one server fails. 

2. Question about the software: Is it possible to send the MPU data via i.e. TCP to OpenPlotter, using OP's calibration funktionality? (MPU - wifi - server case)

I would be happy to hear your expertise.

p.s.: I'm testing by myself. But I damaged one of my two Raspis and have to wait for replacement.

[skipper@sy-barranas]

The server -> server connection can produce loops. Right?

[seandepagnier]

I strongly suggest you attach the mpu9250 to a raspberry not an esp8266. But please feel free to experiment of course.

The reason is, the raspberry has the cpu power and algorithms already implemented to automatically calibrate and manage the mpu9250 efficiently.

If you were to say send the raw sensor data over wifi from the esp8266 it would incur lag which is a very bad thing. I definitely do not want to read the gyro, send it over wifi, then have the autopilot react to that. it would degrade performance. In fact, it is setup now, so that pypilot directly reads the mpu9250 in a real-time priority process and drives the motor directly with a latency less than 0.1 seconds, and distributes the data on a low priority process to other tools where latency is not an issue.

So depending on your use case, and what you are trying to accomplish it might make sense. I hope this is clear and please continue the discussion.

[ddelorme]

I agree with Sean. Power becomes an issue too. I have some sensors connected to a esp32 but I really fight to keep my power usage down. Since openplotter stays on when i am on the boat. I would not worry too much about the CPU It can handle a good load.. OPCN is the biggest hog but it fits and much better after the last update.
My install runs in the 5% range 40 to 50% with OPCN running.
As Sean said lag on the MPU would be bad.
I use a esp32 for a wind sensor via wifi with little lag but i am still testing. transmission lag runs about 20 to 50 mills though a router and switch to a RPI. But i would not use my MPU like this.

I also keep a spare board/boards so if something dies I can just replace and fix later.
And being old school I have a paper chart and hand compass. that I update as i sail just in case...
Sigsens has some code for a mpu but I would talk with them on how well it works?