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Reverse-Engineering the LCD Display Interface of the Nest 2nd Gen Thermostat

sett.homes

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Re: Reverse-Engineering the LCD Display Interface of the Nest 2nd Gen Thermostat

#21

Post by tchebb »

z3ugma wrote: post #4

Author here, if anyone has deeper questions

Is there a reason you wired MOSI and MISO together with a resistor instead of setting the SPI_SIO bit in the ESP32C6's SPI controller? The reference manual[1] says that bit enables "3-line half-duplex communication, where MOSI and MISO signals share the same pin" (page 866). I'm not sure if it's suitable, since the half-duplex mode (see section 28.5.8.4) seems to be designed mainly for talking to SPI flash chips.

[1] https://www.espressif.com/sites/default/files/documentation/...

Re: Reverse-Engineering the LCD Display Interface of the Nest 2nd Gen Thermostat

#22

Post by z3ugma »

tchebb wrote: post #21
z3ugma wrote: post #4

Author here, if anyone has deeper questions

Is there a reason you wired MOSI and MISO together with a resistor instead of setting the SPI_SIO bit in the ESP32C6's SPI controller? The reference manual[1] says that bit enables "3-line half-duplex communication, where MOSI and MISO signals share the same pin" (page 866). I'm not sure if it's suitable, since the half-duplex mode (see section 28.5.8.4) seems to be designed mainly for talking to SPI flash chips. [1]…

Good idea - I can take this to the developers of Toit lang https://toitlang.org/ which is the stack I'm using and is built atop of ESP-IDF

Re: Reverse-Engineering the LCD Display Interface of the Nest 2nd Gen Thermostat

#23

Post by paco3346 »

userbinator wrote: post #20
two_handfuls wrote: post #19

Earlier quoted context omitted.

The article says the display is physically round.

The pictures tell a different story.

The display itself is round, although the module is a square with trapezoidal corners.

This is odd because you get the intended shape but not the benefit of the shape. There are plenty of displays that are actually round, such as for smart watches.

I'm curious if Google did this for cost and had decided on a larger bezel from the start.

Re: Reverse-Engineering the LCD Display Interface of the Nest 2nd Gen Thermostat

#24

Post by nom »

paco3346 wrote: post #23
userbinator wrote: post #20

Earlier quoted context omitted.

The pictures tell a different story.

The display itself is round, although the module is a square with trapezoidal corners. This is odd because you get the intended shape but not the benefit of the shape. There are plenty of displays that are actually round, such as for smart watches. I'm curious if Google did this for cost and had decided on a larger bezel from the start.

My guess: it's much easier to cut straight lines. If you don't need it, why go through the more complicated step to cut it circularly.
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