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Assembling Decktility

Note: This document is a work in progress.

Power Manager / Arduino Nano

Firmware

You can build the project with Arduino IDE V2. Change config.h to your liking.

The default (and only) battery and discharge profile is for a Murata VT6 3120 mAh cell. You can leave it in place, but you can also make your own. It is set in powermanager.ino and the default profile is in battery.cpp.

Pinout

The default pins on the Arduino are as follows:

  • Vbat is measured at pin A0.
  • Charge state is measured at pin D2. It connects to the LED connector on the USB-C BMS board. This is marked as LED on the back or D on the front of the PCB.
  • The power enable pin for the mosfet is wired to D3.
  • Vin and Gnd are wired to the common ground and to the switch that connects to the 5 V of the step down converter.
  • A4 is SDA and A5 is SDL. They connect to the Pi on pin 3 (SDA) and pin 5 (SDL). SDA to SDA, and SDL to SDL.

If you use an alternative I2C bus on the Pi, the driver won't scan that bus and it won't work.

Calibrating the voltage

Update the value for VBAT_ADC_MAX_BATTERY_PIN_VOLTAGE depending on the resistors you chose. You must use high resistance values to reduce the current that leaks, as this wire is always connected to the battery. Make sure the pin on the Arduino never gets more than 5V.

I calibrate it as follows:

  • Upload firmare with BATTERY_STATE_LOG enabled in config.h
  • Disconnect USB from Arduino
  • Measure battery voltage with multimeter
  • Reconnect USB to Arduino and observe the voltage readout.
  • Check the difference relative to what you expect, and use that factor to multiply or divide with VBAT_ADC_MAX_BATTERY_PIN_VOLTAGE
  • Repeat the procedure to verify

Raspberry Pi

Add to the following to /boot/config.txt:

dtoverlay=ltc294x,ltc2942,resistor-sense=50,prescaler-exponent=128

Debugging I2C

Manually activate the driver:

modprobe ltc2941-battery-gauge && lsmod | grep ltc

Manually deactiate the driver:

rmmod ltc2941-battery-gauge

Check driver status messages:

dmesg

Retrieve the battery status on the Pi with ic2test.sh.

Kernel driver reference: https://github.com/torvalds/linux/blob/master/drivers/power/supply/ltc2941-battery-gauge.c

Implementation reference: https://github.com/MacroYau/LTC2942-Arduino-Library

Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/ltc2941.pdf

Keyboard mod

The keyboard comes with a Lithium battery installed, but I needed it to work with 5 V. I copied the idea from Yarh.io, but I'll elaborate on it here.

  • Desolder the lipo.
  • Desolder the USB connector. I ended up cutting it off entirely, including the PCB part under it that sticks out.
  • Connect the 5 V pad from the USB connector to the + connector where the lipo was. You can use the pad of the USB connector, but I found it easier to solder directly to the top of R20.
  • Desolder and remove U6. The 2 pads on the bottom right should be soldered together.

keyboard PCB modded

FET module

Build it according to the schematic and PCB placement.

Heat inserts

Insert heat inserts:

  • In the case
  • To the sides of the keyboard top panel
  • On the top of the battery container

Fan

The fan wires are made of plastic. which can melt when soldering. The wires are stiff and runs past the BMS that can get hot. It is advised to cut the wires short and extend back to the desired length with AWG28 silicon wire. Don't forget to add some heat srhink.

Wiring

Wiring is divided into steps, to make it easier to comprehend. Make sure you check continuity on the wires before powering on - especially to make sure there are no short-circuits. Make sure to verify the functionality at each step before continueing to the next.

Double-check your soldering joints, to make sure they are safe. You don't want wires to come loose while you use the device.

Wiring step 1: battery to BMS

The BMS is connected first. Test if the battery is charging properly.

battery to bms wiring schematic

Wiring step 2: BMS to BEC

Now that we have battery power, we'll connect the BEC to step it down to 5V.

bms to bec wiring schematic

Wiring step 3: power

There rest of the power is connected now. The switch powers on the Arduino, while the Arduino powers the FET, which powers the rest of the devices.

The power wiring on the Pi is done directly on the black pin header near the PCB. I start by adding some solder to the base of the relevant pins, before adding the wiring. Make sure the wiring is attached properly, because you don't want it to come loose and create a short-circuit.

general power wiring schematic

Wiring step 4: Arduino

The remaining wires for the Arduino are now connected. It includes I2C, voltage measurement and charging status sensing.

I used 3.9M Ohm for R1 and 2.2M Ohm for R2. If you use different resistor values, you must tweak the firmware settings in config.h of the firmware project. You must use high resistance values to reduce the current that leaks, as this wire is always connected to the battery. Make sure the pin on the Arduino never gets more than 5V.

The Pi wiring for I2C is done directly on the black header connector pins. I used a long and thin TS100 C1 tip to reach these pins.

remaining arduino wiring schematic