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# Sensors

## DHT11 temperature and humidity sensor

1-wire bus protocol, read using https://github.com/szazo/DHT11_Python

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1. Format USB drive using FAT.
2. Copy over all files from the Windows installation DVD, except for `sources/install.wim` - this file is too large to fit on a FAT filesystem.
3. Use https://www.systutorials.com/docs/linux/man/1-wimlib-imagex-split/ tool to split install.wim file into install.swm install2.swm etc.

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# Instructions assume host OS is Fedora Linux.

#
# Clone and build u-boot
#
cd ~/src/
git clone git://git.denx.de/u-boot.git
cd u-boot
sudo dnf install arm-none-eabi-gcc-cs
export ARCH=arm

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To boot from an SD card on Asus C100P Notebook PC, do the following:

1. Prepare the SD card, e.g. `dd` an OS image onto it and insert it into the notebook.
2. Enable developer mode: turn notebook on while holding Esc+F3(Refresh), after it turns on press Ctrl+D to switch to developer mode.
3. Open a shell (Ctrl+T in Chrome), type `shell` to launch bash, do `sudo crossystem dev_boot_usb=1 dev_boot_signed_only=0`, reboot.
4. At the boot prompt with the developer mode warning, press Ctrl+U to boot from the SD card.

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1. Download a Fedora Linux for ARM image.

2. Install fedora-arm-installer:
    dnf install fedora-arm-installer

3. Write the image to SD card, not forgetting to set the console to serial port:
    fedora-arm-image-installer \
        --image=Fedora-Minimal-armhfp-25-1.3-sda.raw.xz \
        --target=wandboard \
        --media=/dev/sdc \

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These instructions describe how to install an Android toolchain capable of compiling standalone C/C++ programs for an Android device.

1. Download Android NDK from https://developer.android.com/ndk/downloads/index.html and unpack it somewhere.

2. Run the included script to install a standalone toolchain:
    mkdir $HOME/opt
    $NDK/build/tools/make-standalone-toolchain.sh --arch=arm --install-dir=$HOME/opt/android_toolchain

3. Create a test program and compile it:
    cat > hello.c << EOF

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0: Key name.
1: Flags? Keys which have c0 as first byte are usually
   writeable. Second byte seems to be the length of value.
2: Key type.
3: More flags?
4: Value. ``x'' means value could not be read.

0    1        2    3        4
#KEY 88040000 ui32 acb20200 00 00 02 31 
$Adr 88040000 ui32 20070020 00 00 03 00