Skip to content

Latest commit

 

History

History
81 lines (63 loc) · 3.83 KB

README.md

File metadata and controls

81 lines (63 loc) · 3.83 KB
Raw

AtomVM DHT Example Program

Welcome to the dht_example AtomVM application.

This example application will drive a DHT11 or DHT22 temperature and humidity sensor attached to an ESP32 device using a single data wire and print readings to the console.

The dht_example program illustrates use of the DHT API by taking a temperature and humidity reading every 30 seconds, and displaying the result on the console.

For this application, you will need:

  • An ESP32 device, flashed with the AtomVM image (including the VM and core libraries), containing the atomvm_dht Nif, and capable of connecting via UART to your development machine;
  • A DHT11 or DHT22 device, typically marketed as an integrated development board;
  • The esptool.py tool (for flashing);
  • The git version control tool;
  • Erlang/OTP 21 or higher, along with rebar3;
  • A serial monitor program of your choice (e.g, minicom)

Note that you will need to build a version of the AtomVM virtual machine that includes the atomvm_dht Nif.

Getting Started

Connection

To run this example program, connect the positive (+) lead on the DHT device to +3.3v power on the ESP32, the negative lead (-) to a ground pin on the ESP32, and the data pin to GPIO pin 22 on the ESP32 device.

+-----------+                           +-----------+
|           o-------- +3.3v ------------o VCC       |
|   DHT11   o-------- data -------------o IO21      |
|     or    o-------- unused            |           |
|   DHT22   o-------- gnd --------------o GND       |
|           |                           |           |
+-----------+                           |           |
                                        |   ESP32   |
                                        +-----------+

Build Instructions

To build and flash this application to your ESP32 device, issue the esp32_flash target to the rebar3 command, and optionally specify the device port and baud rate, if they do not match the defaults.

Note. For information about the esp32_flash target, see the atomvm_rebar3_plugin instructions.

shell$ rebar3 atomvm esp32_flash -p /dev/ttyUSB0 -b 115200
===> Fetching atomvm_rebar3_plugin
===> Fetching packbeam
===> Analyzing applications...
===> Compiling atomvm_rebar3_plugin
===> Compiling packbeam
===> Verifying dependencies...
===> App atomvm_lib is a checkout dependency and cannot be locked.
===> Analyzing applications...
===> Compiling atomvm_lib
===> Analyzing applications...
===> Compiling dht_example
===> AVM file written to : atomvm_lib.avm
===> AVM file written to : dht_example.avm
===> esptool.py --chip esp32 --port /dev/ttyUSB0 --baud 115200 --before default_reset --after hard_reset write_flash -u --flash_mode dio --flash_freq 40m --flash_size detect 0x210000 .../atomvm_lib/examples/dht_example/_build/default/lib/dht_example.avm

esptool.py v2.1
Connecting........_____.
Chip is ESP32D0WDQ6 (revision (unknown 0xa))
Uploading stub...
Running stub...
Stub running...
Configuring flash size...
Auto-detected Flash size: 4MB
Wrote 16384 bytes at 0x00210000 in 1.4 seconds (91.4 kbit/s)...
Hash of data verified.

Leaving...
Hard resetting...

Connect to the device using the USB port (e.g., via minicom), and you should see something like:

Found AVM partition: size: 1048576, address: 0x110000
Booting file mapped at: 0x3f430000, size: 1048576
Starting: dht_example.beam...
---
Temperature: 21.3C  Humidity: 41.6%
Temperature: 21.4C  Humidity: 41.4%
Temperature: 21.3C  Humidity: 41.3%
...