+This post sat in drafts for years, and is being published as-is. I might update it at some point, but probably not. Sorry! +
+{{< /raw >}} + +There are a lot of reasons I might not want someone to knock on or open my office door. +I work from home, which means meetings get interrupted. I have sensory processing issues, +which means sometimes I can barely deal with human voices. I have an anxiety disorder, +which means other times I can't deal with, well, human interaction. + +Maybe it's stir-craziness during quarantine, or maybe this is just who I am, but I decided +to solve this problem in the most convoluted way I could think of. So I wrote a server and +arduino client for controlling gpio pins over wifi, and built myself a status indicator light. + +## The build + +Here is the initial prototype: + +{{< imgproc "breadboard.jpg" >}} + Breadboard with wires, LEDs, resistors, and a microcontroller. +{{< /imgproc >}} + +After some cleanup (and adding a fourth light) we get this nice little box: + +{{/*< imgproc "wiring.jpg" />*/}} +{{/*< imgproc "finished.jpg" />*/}} + +## The code + +I tried to keep the code generic, but not too generic. I could have had the webhook server just record and relay +an arbitrary string, for instance. But the server needs to be aware of 'momentary' switches, (for future ideas +I have) and I want some sort of input validation, so instead the server expects a simple little json array. + +The client code currently only works on ESP8266 chips. (specifically, my prototype is an Adafruit Feather Huzzah) +One 'fun' thing about the ESP8266, and more broadly Arduino programming in general, is that there are a lot of +different libraries that can be used to achieve the same thing, with varying levels of ease and documentation. Getting +HTTPS to work was surprisingly challenging, and I briefly went down a rabbit-hole of Arduino filesystems and hex-encoded +CA certificates before discovering BearSSL's WiFiClientSecure library. + +The server code is [here](https://git.annabunch.es/annabunches/gpio-webhook-server) and the client code is +[here](https://git.annabunch.es/annabunches/gpio-webhook-arduino). + +## Triggering the webhook + +Anything that can POST to a URL can be used to write to the webhook and change the light. I'm using [IFTTT](https://ifttt.com)'s +Amazon Alexa integration, which seems to be the easiest way to get an Alexa to send a webhook. + +## Understanding the pin mapping + +The `PIN_MAP` variable in `config.h` needs to be configured based on the particular board you're using, and which GPIO pins +you've decided to use for that board. As mentioned above, this project is using an Feather Huzzah with the ESP8266 chip. +The pinout for that board looks like this: + +{{< imgproc pinout.png >}} +Pinout diagram for Feather Huzzah ESP8266. Copyright Danny Nosonowitz. Original available [here](https://learn.adafruit.com/assets/46249"). +{{< /imgproc >}} + +I'm using the "bottom" four pins on the right-hand side, pins 4, 5, 2, and 16. So `PIN_MAP` looks like this: + +{{< highlight C >}} +{ + {4, 1}, // green + {5, 1}, // yellow + {2, 1}, // red + {16, 1} // blue +}; +{{< /highlight >}} + +The order in this array determines which pin maps to each webhook data point. For example, if the webhook data received looks like `[1,0,1,0]`, that would turn on the green and red lights. + +## Security Concerns + +Don't use this code for anything critical! The only protection this has against malicious input is the webhook +URL being kept a secret. Assuming your webhook server is either kept on your local network or secured behind an HTTPS proxy, +that should be a reasonable guarantee, but it's still a fairly shaky amount of security. I considered requiring POST requests +to be signed by a secret certificate of some sort, but that would rule out using something as simple as IFTTT to send the webhooks. So instead, +I've sacrificed a measure of security for ease of use. diff --git a/content/posts/2020-05-15-gpio-webhook/pinout.png b/content/posts/2020-05-15-gpio-webhook/pinout.png new file mode 100644 index 0000000..6201bad Binary files /dev/null and b/content/posts/2020-05-15-gpio-webhook/pinout.png differ diff --git a/layouts/shortcodes/imgproc.html b/layouts/shortcodes/imgproc.html new file mode 100644 index 0000000..1c4b154 --- /dev/null +++ b/layouts/shortcodes/imgproc.html @@ -0,0 +1,20 @@ +{{ $original := .Page.Resources.GetMatch (printf "*%s*" (.Get 0)) }} +{{ $imgdata := imageConfig (printf "/content/%s" $original.RelPermalink) }} +{{ if (gt $imgdata.Width 1500) }} + {{ .Scratch.Set "image" ($original.Resize "1500x") }} +{{ else if (gt $imgdata.Height 1500) }} + {{ .Scratch.Set "image" ($original.Resize "x1500") }} +{{ else }} + {{ .Scratch.Set "image" $original }} +{{ end }} + +{{ $image := .Scratch.Get "image" }} + +