The Joy of Connecting Elixir to the Physical World

Transcript

1. Frank Hunleth @fhunleth The Joy of Connecting Elixir to the Physical World
2. Frank Hunleth @fhunleth How to avoid pain and agony with hardware…
3. Agenda ▸ Three routes to hardware with Elixir ▸ Nerves ▸ Desktop Linux single board computers ▸ Your laptop ▸ Examples ▸ Monitoring your garden via SBC ▸ Finding out where you are via GPS on your laptop ▸ Comparing the routes
4. Nerves Craft and deploy bulletproof embedded software in Elixir
5. Key Nerves attributes ▸ Build tooling and some basic infrastructure for running Elixir on embedded Linux ▸ Start small and build up vs. trim down ▸ Cross-compiled ▸ Elixir and Erlang/OTP libraries and applications over embedded Linux ones (when they exist)
6. Nerves Your Elixir project and dependencies Linux, C libraries, Erlang runtime Nerves System Image OTP release Firmware image
7. Desktop Linux Single Board Computers ▸ Usually low cost ARM boards with hardware-friendly I/O ▸ Raspberry Pi, Beaglebone Black, probably 100 others ▸ Most distributed with Debian or a Debian-derived distributions like Raspbian ▸ Work like real computers What I learned the hard way: Don’t choose a board just based on hardware specs
8. The great part about Debian Pretty much everyone else uses it so it usually works well, has tutorials, and large user communities But, you probably will need to build Erlang from scratch. 
9. Agenda ▸ Three routes to hardware with Elixir ▸ Nerves ▸ Desktop Linux single board computers ▸ Your laptop ▸ Examples ▸ Monitoring your garden via SBC ▸ Finding out where you are via GPS on your laptop ▸ Comparing the routes
10. Example ▸ What do you do if you forget to water your plants, but have a Raspberry Pi handy? ▸ Answer: Connect a moisture sensor to the Pi to monitor it and push notifications to your phone, of course.
11. Hooking it up ▸ MCP3008 converts analog measurements to digital ▸ Use the SPI pins on the Raspberry Pi for input ▸ Read values using elixir_ale Analog Digital SPI
12. What does elixir_ale want for SPI?
13. Get the datasheet
14. Figure out what to transfer
15. Figure out what to transfer 1 Start bit
16. Figure out what to transfer 1 mode bit 1 Start bit
17. Figure out what to transfer 3 input address bits 1 mode bit 1 Start bit
18. Figure out what to transfer 3 input address bits 1 mode bit 1 Start bit 10 bits in the result
19. Figure out what to transfer 3 input address bits 1 mode bit 1 Start bit 1 bit between request & response 1 bit that is zero 10 bits in the result
20. Figure out what to transfer 3 input address bits 1 mode bit 1 Start bit 1 bit between request & response 1 bit that is zero 10 bits in the result 1+1+3+1+1+10 = 17 bits????
21. Try #2 - Find app note
22. Try #2 - Find app note
23. Try #2 - Find app note 3 bytes!
24. The code mode = 0 # Single-ended mode sensor = 2 # Try this sensor <<_::size(14), value::size(10)>> = Spi.transfer(pid, <<0x01, mode::size(1), sensor::size(3), 0::size(12)>>) IO.puts "Sensor #{sensor} measured #{value}”
25. Agenda ▸ Three routes to hardware with Elixir ▸ Nerves ▸ Desktop Linux single board computers ▸ Your laptop ▸ Examples ▸ Monitoring your garden via SBC ▸ Finding out where you are via GPS on your laptop ▸ Comparing the routes
26. Physical computing from your laptop ▸ No need to change your development routine ▸ Many sensors and actuators supported ▸ The catch ▸ Your laptop is connected ▸ Interface can be slow
27. The UART ▸ Universal Asynchronous Receiver/Transmitter ▸ Three main wires: receive, transmit, and ground ▸ Provides a byte stream connection like TCP except: ▸ You or someone else wires up the connection ▸ Both sides need to agree on the connection speed and parameters ▸ Bytes get dropped and bits get corrupted sometimes ▸ Sometimes you get flow control
28. The UART ▸ Dirt simple technology that’s still ubiquitous in embedded ▸ Inexpensive and well-supported ▸ Easy to debug ▸ Wired, but wireless options that look nearly identical to software
29. USB to serial cable ▸ Key attributes ▸ Logic voltage level - 5V or 3V ▸ 6 pin header vs. wires ▸ 5 V power supply? ▸ FTDI, Prolific, or clone chip ▸ Sold by Adafruit, Digikey, Microcenter, Mouser, Sparkfun, etc. ▸ Except for the clone chip versions, all work on Linux, Mac, and Windows
30. Where am I? ▸ Use GPS! ▸ Most modules provide a UART interface (GND, RX, TX) ▸ If the modules accepts 5 V, power it from the USB to serial cable ▸ Position data (and more) comes across as NMEA-0183 strings
31. A taste of nerves_uart iex(1)> Nerves.UART.enumerate %{"ttyUSB0" => %{description: "USB-Serial Controller", manufacturer: "Prolific Technology Inc.", product_id: 8963, vendor_id: 1659}}
32. A taste of nerves_uart iex> {:ok, uart}= Nerves.UART.start_link {:ok, #PID<0.186.0>} iex> Nerves.UART.open(uart, "ttyUSB0", speed: 9600, active: false) :ok
33. A taste of nerves_uart iex> Nerves.UART.read(uart) {:ok, "$PGTOP,11,2*6E\r\n$GPGGA,000204.800,,,,,0,0,,,M,,M,,*46\r\n$GPGSA,A,1,,,,,,,,,,,,,,,*1E\r\n$GPRMC,0002 04.800,V,,,,,0.00,0.00,060180,,,N*4C\r\n$GPVTG,0.00,T,,M,0.00,N,0.00,K,N*32\r\n$PGTOP,11,2*6E\r\n$GPG GA,000205.800,,,,,0,0,,,M,,M,,*47\r\n$GPGSA,A,1,,,,,,,,,,,,,,,*1E\r\n$GPRMC,000205.800,V,,,,,0.00,0.00,06018 0,,,N*4D\r\n$GPVTG,0.00,T,,M,0"}
34. A taste of nerves_uart iex> Nerves.UART.configure(uart, active: true) :ok iex> flush {:nerves_uart, "ttyUSB0", "$"} {:nerves_uart, "ttyUSB0", "P"} {:nerves_uart, "ttyUSB0", "G"} {:nerves_uart, "ttyUSB0", "T"} {:nerves_uart, "ttyUSB0", "O"} {:nerves_uart, "ttyUSB0", "P"} {:nerves_uart, "ttyUSB0", ","} {:nerves_uart, "ttyUSB0", "1"} {:nerves_uart, "ttyUSB0", "1"} {:nerves_uart, "ttyUSB0", ","} {:nerves_uart, "ttyUSB0", "2"} {:nerves_uart, "ttyUSB0", "*"} {:nerves_uart, "ttyUSB0", "6"} {:nerves_uart, "ttyUSB0", "E"} {:nerves_uart, "ttyUSB0", "\r"} {:nerves_uart, "ttyUSB0", "\n"}
35. A taste of nerves_uart iex> Nerves.UART.configure(uart, framing: {Nerves.UART.Framing.Line, separator: "\r\n"}) :ok
36. A taste of nerves_uart iex> flush {:nerves_uart, "ttyUSB0", "$PGTOP,11,2*6E"} {:nerves_uart, "ttyUSB0", "$GPGGA,000417.800,,,,,0,0,,,M,,M,,*42"} {:nerves_uart, "ttyUSB0", "$GPGSA,A,1,,,,,,,,,,,,,,,*1E"} {:nerves_uart, "ttyUSB0", "$GPRMC,000417.800,V,,,,,0.00,0.00,060180,,,N*48"} {:nerves_uart, "ttyUSB0", "$GPVTG,0.00,T,,M,0.00,N,0.00,K,N*32"} :ok
37. What else can a USB->Serial cable do? ATDT5551212
38. The Hayes AT command set lives! ▸ Bluetooth - Talk to your phone ▸ Serial port extenders++ like the RN-42 ▸ BLE modules like Adafruit’s Bluefruit ▸ Cellular modems - Talk to the nearest cell tower ▸ SparqEE, LinkSprite, Adafruit ▸ Satellite modems - Talk to a nearby Iridium satellite ▸ RockBLOCK
39. nerves_uart to an Arduino ▸ Install the firmata firmware on the Arduino ▸ UART protocol for controlling pins ▸ https://github.com/firmata/protocol ▸ Elixir even has a firmata library ▸ https://github.com/kfatehi/firmata ▸ Looking for a maintainer
40. Common embedded system architecture Hard real-time Microprocessor (ARM Cortex, x86, etc.) Microcontroller (ARM M3, ATmega) Soft real-time Elixir C/C++ UART
41. Agenda ▸ Three routes to hardware with Elixir ▸ Nerves ▸ Desktop Linux single board computers ▸ Your laptop ▸ Examples ▸ Monitoring your garden via SBC ▸ Finding out where you are via GPS on your laptop ▸ Comparing the routes
42. Comparing approaches Laptop + nerves_uart Desktop Linux SBC Nerves Edit/build/test cycle Host Target Edit/build on host, run on target System specs Modern laptop ~700 MHz+ w/ GB of storage 300-400 MHz+ 32 MB+ Supported devices Limited to UART- based HW, firmata Lots out of the box Lots, but may need to be added Tools You have them already Manually build Erlang Nerves provides compilers Deployment Share code Disk image and .deb files Firmware image file When I use it Full featured dev environment; Easiest to unit test Quick debugging of low level hw Small, focused, built for making products
43. Where to find out more ▸ Project pages: ▸ https://github.com/nerves-project/nerves_uart ▸ https://github.com/fhunleth/elixir_ale ▸ Twitter: @NervesProject and @fhunleth ▸ #nerves channel on the elixir-lang slack ▸ Nerves and embedded Linux consulting/development fhunleth@troodon-software.com