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If one drives a early 90's car, its perfectly acceptable to drive analog gauges with PWM. For the newer ones , tought, control is made digitally.
The cluster I use sends a pulse every so often (about 20Hz) and measures some drop in voltage from the float level and temperature sensor. It expects the signal to be zero otherwise. Driving it with PWM won't work as the cluster CPU is expecting a signal within a certain range/voltage. Some have an internal current source.
This is something to have in consideration while designing a universal controller. In my opinion its easier to have a digital controller and just make bar graphs. Speedometer and tachometer are generally digital and can be interfaced easily. I have a digital readout on display to accommodate older cars that may have a mechanical tachometer. This is used to calculate SoC and remaining mileage. Total mileage and SoC are saved to an FRAM by an interrupt at shut down. This takes a fraction of the time needed to write a standard EEPROM.
In general I find it best to keep the cluster and controller separate. The controller can use CAN or whatever to send a limited amount of data, but the display has its own CPU.
As for my controller, I'm very pleased that a version of the ILI9341 controller is now available for a 2.8" display. I recomend using this as a starting point. With a co troller supporting DMA one can get a very decent speed in a much more compact form than using parallel access. I'll be probably moving the whole thing to a cortex CPU soon.
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