What I did first on NodeMCU was connecting to the Internet, but usually blinking an LED is the “hello world” in the microcontroller world. So let’s do it.
Connecting an LED
Parts:
- Node MCU Developer Kit
- LED
- Resistor
The circuit is pretty simple.
- Connect the Node MCU’s D1 (GPIO) to the LED’s longer lead (anode)
- Connect the LED’s shorter lead (cathode) to the resistor
- Connect the resistor to the Node MCU’s GND
luatool is a small Python script
that communicates with NodeMCU.
Instead of using pySerial’s miniterm.py interactively, you can use luatool
to upload your Lua script to the device.
luatool needs pySerial. The install instruction is in
my previous post.
% git clone https://github.com/4refr0nt/luatool
...
% cd luatool
% python luatool/luatool.py --port /dev/cu.SLAB_USBtoUART --id
->=node.chipid() -> send without check
1187795
%
Why using infinite loops is a bad idea?
Once you have luatool, you can write a Lua script on Emacs (or your favorite editor, but isn’t it Emacs?) and upload the script to the device.
To blink an LED, the simplest solution is just having an infinite loop like below.
LED_PIN = 1
US_TO_MS = 1000
gpio.mode(LED_PIN, gpio.OUTPUT)
while true do
gpio.write(LED_PIN, gpio.HIGH)
tmr.delay(500 * US_TO_MS)
gpio.write(LED_PIN, gpio.LOW)
tmr.delay(500 * US_TO_MS)
end
Sending the script by using luatool…
% python luatool/luatool.py --port /dev/cu.SLAB_USBtoUART --src ~/blink.lua --dofile
...
->dofile("blink.lua") -> send without check
--->>> All done <<<---
%
It does work, but then you will realize that you can’t upload anything from
luatool.
The reason is, luatool is doing all operations by just sending Lua code.
Once you execute a script that has an infinite loop,
The Lua interpreter on the device can’t receive any new code due to the loop,
and it makes luatool unusable.
Use tmr.alarm instead
Actually NodeMCU’s reference clearly metiones that on tmr.delay’s section.
Busyloops the processor for a specified number of microseconds.
This is in general a bad idea, because nothing else gets to run, and the networking stack (and other things) can fall over as a result.
Instead you can use
tmr.alarm that wraps
tmr.register and
tmr.start.
Here is the new script. EXPR and A or B is
Lua’s ternary operator equivalent idiom.
LED_PIN = 1
gpio.mode(LED_PIN, gpio.OUTPUT)
value = true
tmr.alarm(0, 500, 1, function ()
gpio.write(LED_PIN, value and gpio.HIGH or gpio.LOW)
value = not value
end)
If your previous script is running, you need kill that by clicking RST (Reset) on the device, before using luatool.
% python luatool/luatool.py --port /dev/cu.SLAB_USBtoUART --src ~/blink.lua --dofile
...
->dofile("blink.lua") -> send without check
--->>> All done <<<---
%
It looks same, but unlike before, you can use luatool even this script is running.
