The idea about this project is to combine all additional features you could need on a handheld machine but keeping modification on the motherboard as low as possible.
The PCB borders, headers position, CPU heatsink clearance and L2/R2 switches positions are the same.
This addon board embed a USB Nanohub with 2 ports, a BL-R8188FU3 WiFi module (RTL8188FTV with IPEX connector), a DS3231M RTC chip, 3 MCP3021A ADC chips (2 chips for the the Joystick and one for the battery monitoring), a 16x16x4.5 fan (the same used in the original addon board). Revision 3 now use a ADS1015 to allow use of 2 joystick at the same time.
Due to USB hub and WiFi module needing to be in the USB header side, the fan position has been switch to the other side of the CPU heatsink but because of this the hotkey switch needed to be moved as well. A AMS1117-3.3 is used to power the WiFi module and the ADC chips reading the joystick position.
Following recommendation from Flavor (https://github.com/TheFlav), the ADC chip used to monitor battery voltage is running at 4.5v using a MAX6107 voltage reference chip. The battery voltage also feed the VBAT pin on the RTC chip, the power consumption when the console is off is negligible.
The fan is still controlled with pin 40 using a NPN transistor.
*.cb files can be open with CamBam CNC Software (http://www.cambam.info/).
- rev0 : initial version, ADC chip placed the wrong way, voltage divider used to power battery monitoring chip.
- rev1 : partial file, traces rework, ADC chip used to monitor battery run at 5v (could not work because I2C bus run at 3v3).
- rev2 : traces reworked, ADC chip used to monitor battery run at 4.5v via a voltage reference chip, this revision work fine in the real world.
- rev3 : X and Y ADC chips replace by a ADS1015 to allow use of 2 joystick with adress 0x48, AMS1117-3.3 regulator now use 22µF capacitor.
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Battery monitor : After testing, using MCP3021A (10bits) is a better choise than using MCP3221A (12bits). MCP3221A look to be more sensible to input noise, you can get more precise values (12bits vs 10bits) but with at the same time a more wide error. A good example of this is when the handheld is charging, while MCP3021A is able to report 4.20-4.22v, MCP3221A does report 4.30v. This error doesn't look that big but when monitoring a Li-ion battery, you can easily lost or gain 15% error on the battery level reports.
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rev3 : While MCP3021A value goes from 0 (0v) to 1024 (extrapolate to 4096) (+3.3v), ADS1015 base its read on the Full-Scale Range (FSR) set by the user (in this case ±4.096V), this mean that the ADC chip has a readable values in this PCB case goes from 2048 (0v) to 398 (-3.3v) OR to 3698 (+3.3v), so a range of only 1650. I used this chip not for it's performance but for it footprint. To avoid lag, use a udelay(450) insead of msleep(1) in your driver code.
- Battery monitoring board : provide a MCP3021A ADC chip (or a MCP3221A) with a MAX6107 voltage reference chip (Note: this board doesn't embeb pullup resistors, it is design to be used with original Freeplay CM3 Addon board).
- Fan control board : a simple GPIO board with a resistor and a NPN transistor.