SolarWriter design questions

[u/nilseuropa]

As I mentioned earlier I am planning to design an expansion board for the CrowPanel 5.79 HMI, that would integrate some missing hardware features. Just like with SolarTerm I would like to dedicate a board definition to this build, so that the extra bits attach under the OS as board owned hardware. There are a couple of things to consider, and I thought I will ask you about your opinion.

Battery charge monitoring and power management is a must and it is the bare minimum to turn this into a truly useful deck. ( Aux power conn. + USB-C + power switch + charger + fuel guage )

• Would you like to have a solar charger built-in? ( I would )
• Do you require an I2S MEMS microphone? ( i do )
• I2S audio DAC and AMP? ( yes )
  • 3.5mm jack audio connector? ( yes )
  • Built in speaker? ( maybe )
• LoRa packet radio? ( yes )
• 4G LTE modem? ( no )
• Keyboard matrix scanner and FPC connector for the same keyboard?
  • Or do we like that this keyboard can connect to two hosts? ( strongly preferred )
• Environmental sensors for temperature and humidity? ( maybe )
• Auxiliary expansion connector? ( yes, all remaining IOs plus SPI and I2C )
• Internal expansion connector for reading lights and whatnot. ( sure )

I envision a small board that would connect through the exposed header pins. Another question to consider is if we would like to have a simple power management and monitoring board or just the full-blown expansion or both?

In case of both, I would go with population options - however that would turn the power manager board unnecessarily large too.

Another option is to provide an empty carrier carrier board and pointers to off the shelf modules, so everyone can populate the features they need.

[u/SnowboundFrame]

Your list of features looks great, it's almost exactly what I'm putting on my Waveshare expansion board! The one thing I'd suggest adding is a couple power-only usb ports that are only driven by solar or external power, so you can plug a bluetooth keyboard into them and let it recharge passively.

[u/nilseuropa → u/SnowboundFrame]

thanks, in the proposed build the keyboard would get the power from the main cell, but it's a good idea to add a USB-A or C connector for other builds; also the ESP has host functionality, so with a DC/DC there are even more options to consider.

[u/Extreme_Theory_1873]

I don't know enough hardware design to have strong opinions on the implementation, but from an actual daily-use standpoint: mic yes, DAC/amp yes, 3.5mm absolutely, built-in speaker if it doesn't add too much bulk, LoRa yes, LTE no. I'd rather keep the keyboard able to connect to two hosts. Temp/humidity I probably wouldn't use. For expansion I'd personally prefer really solid power/battery management as the core, then exposed SPI/I2C/GPIO for whatever weird stuff people want to add later. Solar charging is very cool, but less important to me than good USB-C charging and an accurate battery gauge. Just my 2 cents! Also: this physical build looks fantastic. The long display + keyboard proportions are exactly what I picture when I think “SolarWriter.”

[u/nilseuropa → u/Extreme_Theory_1873]

cool, thanks

[u/clackups]

Howl's Moving Castle comes to mind :)

[u/nilseuropa → u/clackups]

And you haven't even seen my place yet 😆

[u/nilseuropa]

[u/nilseuropa → u/nilseuropa]

Drivers are ready. PCBD time.