pi-printer

About

Pi Printer is a minimal thermal printer server for orange-pi or raspberry-pi or any other SCB compatible board. Background story: we have setup a POS software that connects to a thermal printer via bluetooth. once we got to use it in a real location, e.g. in a shopping mall, we found that there are 20 bluetooth printer/devices around us, and we have difficulties on picking one. and once we connected to the correct printer, we have difficulties on maintaining the connection. thus we come up with a reliable old way of "wired" connection.

How it works

a serverless backend that stores the print jobs. this serverless is hosted in mongodb-atlas, with mongodb-stitch as the serverless functions. the thermal printer is connected to a rasp-pi/orange-pi via USB. this pi-device is connected to the internet via wi-fi, and then the nodejs codes that are deployed in pi-device is the client, which manages print jobs, e.g. pull the jobs, print it, and "removing" the print job.

on another side of it, there is your web app/app that has something that you want to print.(e.g. POS software, ios/android app, etc). this App will send POST request to the serverless backend. this request,then will be stored in the backend, and the printer server will check the updates every 3 seconds and print it if there's any new jobs that still has not been printed.

Pre-requisites

1. SCB (raspberry compatible) e.g orangepi etc. this codes is tested on orangepi zero, using Armbian
2. in the Pi, you have to have git, node, yarn, npm
3. bluetooth thermal printer with mini-usb/usb connection.

Steps

1. create mongodb atlas account here https://www.mongodb.com/cloud/atlas
2. set up a free cluster
3. create mongo-stitch app, set up a webhook for your app/web app to send print job to.
4. set up functions and webhooks for your thermal printer/raspberry-pi/orange-pi to pull print jobs and for the webapp/print job sender
5. set up sentry account for error monitoring
6. set up pm2 account for orange pi monitoring
7. run the print server

Step Explanations

1 create mongodb atlas account

create mongodb atlas account here https://www.mongodb.com/cloud/atlas it has to be mongodb atlas because we are depending on mongo-stitch.

2 create free mongodb cluster

once you created an account there, you are allowed to create 1 free mongo-db cluster. so now, create it. put it in a region close to where your printer is located.

3 create stitch app

once you created the cluster,

• go to Services -> stitch
• create new application,
• give it app name, link to your created cluster, name the service.
• select local deployment model.
• select primary region, pick the same/closest to where you setup your cluster.

4 configure stitch app

once the application is created, click on it, and you go to the stitch dashboard.

• take note your APP ID
• initialise a mongoDB collection. fill in Database name with printer and Collection name jobs
• create rules, pick your database, and collection, make sure that you have write access

4.1 Create users (API users from API user providers)

• you need to create 2 different users, 1 for the webapp/the one who sending in printer jobs. and the 2nd is for the orange-pi.
• go to providers tab, click on API Keys.
• enable it, if not enabled yet.
• click create api key
• name the 1st one, printer take note the key, prepare it for the orange-pi
• click create api key again to create the 2nd one.
• name the 2nd one, e.g. web_app take note the key, prepare it for your web-app/print job sender.

4.2 Create getQueues Functions

• functions is a serverless API/RPC where you can call from the client with the stitch-sdk
• go to functions -> create new function -> name it getQueues
• authentication application authentication
• make sure private is disabled
• go to function editor and paste in content from your repo stitch/function/getQueues.js

4.3 Create setIsPrinted Functions

• go to functions -> create new function -> name it setIsPrinted
• authentication application authentication
• make sure private is disabled
• go to function editor and paste in content from your repo stitch/function/setIsPrinted.js

4.4 Create print-service Webhook

Webhook is a public facing API or a https based serverless API. your web app/print job sender supposed to be able to send POST request to this webhook as a way to send the print job.

• go to 3rd party service -> add incoming webhook
• name it add-print-job
• authentication application authentication
• take note the Webhook Url
• set HTTP method to POST
• respond with result to ON
• request validation can be No additional authorization
• go to function editor and paste in content from stitch/webhook/add-print-job.js

4.5 Deploy

once you saved all of those, don't forget to press deploy on the top of the window.

5 setup sentry account

we are using sentry as one of the transport of our logger. the printer server will be placed remotely thus we need a little bit of visibility in term of when there's error/exception on our printer server.

• please go to https://sentry.io/ and create a free account, and login.
• take note the sentry dsn

6 setup pm2 in the printer server (orange-pi)

• register an account https://id.keymetrics.io/api/oauth/register
• login, then add new bucket.
• on top right, you see connect button, take note the linking command to link your printer to this monitoring tool. pm2 link xx5522 xx1234

7 run the printer server

• connect the thermal printer via mini-usb to usb part of orange-pi/raspberry-pi. in my case, the usb device assigned is /dev/usb/lp0 reference: https://mike42.me/blog/2015-03-getting-a-usb-receipt-printer-working-on-linux

• ssh to your orange-pi/raspberry pi, git clone this repo from there.

• make sure you have node, npm, yarn in your orange-pi/raspberry-pi

• install pm2. npm install -g pm2

• paste the linking command and execute it.

• yarn install

• setup .env file as your config file. cp .env.dist .env now copy paste your keys/dsn that you noted above into this .env file.

• run the printer server with pm2. pm2 start main.js

• save the task to pm2 service manager. pm2 save

• orange-pi/raspberry-pi are devices that easily restartable, and difficult to connect to, so we can set it up as a startup script. pm2 startup, copy the response, and paste and execute in the terminal. when there's error at a later point of the running time, you can just unplug the power, then replug it.

WebApp/printer client/print job sender

this is a client / software that sends print job to the printer server. thanks to the webhook that we set above, we can just send a POST request to it, and once it received by the mongodb-stitch, your printer server will print it straight away.

example request
POST
https://ap-southeast-2.aws.webhooks.mongodb-stitch.com/api/client/v2.0/app/printer-abcd/service/printer-service/incoming_webhook/add-print-job

body:

{
  "api-key": "api-key-secret-akn20380-1--2980020",
  "jobContent": "print this"
}