System Design
After some reasonably careful thought, I have come up with a tentative design for the system...
The recessed area of the dashboard where the current instrument cluster sits is just about the size of two large phones. It seems to me that economies of scale have made phones reasonably inexpensive, as well as being reasonably robust and very compact. So the plan is to pick up a couple phones to use for the display of the digital dash.
The signals from the car are both analog and digital. They add up fast! It seems to me that 16 digital lines (by "digital" I just mean ON or OFF) and 8 analog lines should be enough to receive all the data of immediate interest. The phones have no way of acquiring all those data lines, so I'll need some interface electronics. My plan is to get an inexpensive "discovery" board for a microcontroller (which is designed simply for people to play around with and experiment), and then add some custom electronics to it.
Here is a diagram of the system:
This setup will allow a great deal of flexibility in how the data will be displayed, so I don't have to make any decisions about that right away. My current idea is to put the car's "instruments" (speed, fuel level, error indicators, etc) on one of the phones, and use the other one for GPS-based navigation and other functions (possibly running the "Android Auto" program which seems pretty cool). The instrument display will be a custom Android program that I will write, which will talk to the microcontroller over a USB Serial link (assuming I can get all of that to work).
The recessed area of the dashboard where the current instrument cluster sits is just about the size of two large phones. It seems to me that economies of scale have made phones reasonably inexpensive, as well as being reasonably robust and very compact. So the plan is to pick up a couple phones to use for the display of the digital dash.
The signals from the car are both analog and digital. They add up fast! It seems to me that 16 digital lines (by "digital" I just mean ON or OFF) and 8 analog lines should be enough to receive all the data of immediate interest. The phones have no way of acquiring all those data lines, so I'll need some interface electronics. My plan is to get an inexpensive "discovery" board for a microcontroller (which is designed simply for people to play around with and experiment), and then add some custom electronics to it.
Here is a diagram of the system:
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