developer blog

richard hannagan


After learning how PDFs work, I wrote a cover letter (here's a genericised version) in TextEdit. It looks like this:

![A PDF letter in a Preview window on MacOS](/pdf.png)

Would you also like to write letters in plaintext? Great, here's the code. As you can see it's a lot simpler than you might have expected considering the average PDF you might come across is in the hundreds of kilobytes.

Mine? A miniscule 1,963 bytes. You could store it in the RAM of the Apollo Guidance Computer, twice. Keep scrolling for an explanation of what you're looking at.

```
%PDF-1.0
1 0 obj
<< /Type /Pages
   /Count 1
   /Kids [2 0 R]
>>
endobj
2 0 obj
<< /Type /Page
   /MediaBox [0 0 595 842]
   /Resources 3 0 R
   /Parent 1 0 R
   /Contents [4 0 R]
>>
endobj
3 0 obj
<< /Font
   << /F0
      << /Type /Font
         /BaseFont /Helvetica
         /Subtype /Type1
      >>
   >>
>>
endobj
4 0 obj 
<< >>
stream
BT
    /F0 12 Tf
    400 760 Td
    (My name) Tj
    0 -20 Td
    (My phone number) Tj
    0 -20 Td
    (Melbourne VIC) Tj
    0 -20 Td
    (hello@myemail.com) Tj
    -350 -50 Td
    (30 April 2024) Tj

    0 -50 Td
    (Mr/Mrs Someone) Tj
    0 -20 Td
    (Hiring Manager) Tj
    0 -20 Td
    (REA/MYOB/etc.) Tj

    0 -50 Td
    (Dear Mr/Mrs Someone,) Tj

    0 -40 Td
    (I am writing to express my interest in the [Software Engineer] position at X) Tj
    0 -20 Td
    (as advertised on Seek/LinkedIn. Eager to transition into the tech industry, I am) Tj
    0 -20 Td
    (drawn to the role due to its alignment with my skills and passion for technology.) Tj

    0 -40 Td
    (My proficiency in ...) Tj
    0 -20 Td
    (..., and strong documentation and) Tj
    0 -20 Td
    (scripting skills position me as a candidate well-suited for the dynamic ...) Tj
    0 -20 Td
    (landscape. I believe my ability to communicate complex technical concepts effectively) Tj
    0 -20 Td
    (and collaborate efficiently makes me an ideal fit for your team.) Tj

    0 -40 Td
    (I am excited about the opportunity to contribute to X's something) Tj
    0 -20 Td
    (initiatives and would appreciate the chance to discuss how my skills align with the role) Tj
    0 -20 Td
    (in more detail.) Tj

    0 -40 Td
    (Thank you for considering my application. I look forward to the possibility of an) Tj
    0 -20 Td
    (interview.) Tj

    0 -50 Td
    (Sincerely,) Tj
    0 -40 Td
    (My Name) Tj
ET
endstream
endobj
5 0 obj
<< /Type /Catalog
   /Pages 1 0 R
>>
endobj
trailer
<< /Root 5 0 R
>>
startxref
%%EOF
```

So a PDF (in the original 1.0 spec) needs to contain 6 objects.  An object starts `1 0 obj` and ends with, you guessed it, `endobj`

The first object defines the document, in this case as being one page in length. The second object defines the shape and size of the page, in this case 595 by 842 points, or the size of an A4 page. The third object defines our font as F0, with Helvetica of course being the best font.

Object 4 is the content. So we're first using our earlier defined F0 and size 12, then without the help of an Adobe Acrobat or similar, we need to manually pick points on the page to write text or draw shapes. We start at 400 points from the left of the page and 760 from the bottom, or roughly the top right of the page where you might write your return address on a real letter. For a new line, simply move 20 points down, or -20. When we get to the date we want to go to the left side of the page, so we're moving -350 points to the left and a bigger line break of -50.

The end of the file is a catalog file, followed by a trailer message and finally a cross-reference table, which we're leaving blank.

Thanks for reading. Now, I must go find a typewriter on Marketplace.

'sit perfectly still, only I may write to PDF' - adobe

writing a PDF cover letter in plaintext


---

### introduction
Meetup, app on phone and ads, pico, e-paper screen, 

> A couple of weeks ago I went to a Python meetup event, and learned about MicroPython, a stripped down version of Python designed to run on microcontrollers. Developed by a guy in Geelong.

> I've had an idea for a while to build a tide-computer of sorts. Why? Where I live there's a canal that's tidal, of course.  A walk along the canal at high tide is like a walk along a beatiful river in Italy. But a visit at low tide smells like trash. A simple screen next to the front door letting you know whether it's a good idea to visit the canal before leaving the house seems it could be just as important as knowing the weather before you leave the house.

> The obvious question is why do I need a whole device dedicated to this one purpose? And my non-answer-answer is why does one need a watch that tells the time and nothing else, when your phone can do that and almost anything else you want.

> In fact, my phone already does this with a relatively clean looking home screen widget. But if you open the app it doesn't display the tide immediately, it first displays an ad. Additionally I just think e-paper/e-ink screens are pretty neat. See: Amazon Kindle.

> So, I purchased a Raspberry Pi Pico and a small 2 inch e-ink screen. People talk about these costing $4 which doesn't really seem to be true but I ended up paying $11.55 plus shipping for the version with pre-soldered headers and with built-in Wifi and Bluetooth, which is pretty ridiculous when you can't get a pint of beer for that little any more.

> So after a couple of days waiting for the postman to pretend I wasn't home and a visit to the post office, here's the development process:

### initial setup
Thonny IDE, would rather use VSCode but this is simpler. Drawbacks like not being able to collapse sections of code. Micropython install.
you can directly interact with the REPL on the Pico

### flashing the LED
Flashing LED is Hello World! Will come in handy later for debugging.

### getting on wifi
![Wi-Fi Setup](/wifi.png)
![Wi-Fi Setup](/wifi_success.png)

### debugging
the LED came in handy for debugging. 
clock not setting when unplugged
timezones
But if ur running the things from computer it sets its clock that was why
It works if I plug the pico into the computer but if I just plug it into a usb power thing only it stops at like     current_time equals utime dot localtime but I dunno why lmk x

![the canal at high tide](/hightide.JPG)
_the canal at high tide_

![the canal at low tide](/lowtide.JPG)
_the canal at low tide_

### getting the data
Getting tide data —> BOM data and rejection message —> just get xml file because same all year
![XML Data](/xml.png)

### parsing the data
xmltok
1 m max tide is so convenient
![xmltok](/xml_parse.png)

### text version
![text version](/text.jpeg)

### resetting at midnight
Time zone/dst
![Resetting at Midnight](/midnight.png)

### working without being plugged in
Thonny sets clock

### fplot
Cwriter vs writer —> driver errors with this thing
getting a time series time graph going
I had to learn waht a generator is

![sine wave](/sine.jpeg)


### final graph display
![final graph display](/graph.jpeg)
![graph](/graph.png)

### secrets.py
wifi password on GitHub —> secrets.py —> .gitignore
![secrets.png](/secrets.png)

### checking if it even works
Screenshot of website to check

### my contribution to nano-gui
I've submitted a pull request to Peter Hinch's micropython-nano-gui repo with my black and white fplot demo. I'll update this post if/when it's accepted. see here: https://github.com/peterhinch/micropython-nano-gui/pull/62

### future
* fix the y-axis labels. I don't really know why I labelled the individual data points.
* 3D print an enclosure, and work out some sort of battery power so I can stick it on a wall near the front door, for a quick glance on the way out. For now it's plugged into my Ikea lamp by the bed.

---

### sources
https://docs.micropython.org/en/latest/rp2/quickref.html

https://datasheets.raspberrypi.com/pico/raspberry-pi-pico-python-sdk.pdf

https://datasheets.raspberrypi.com/picow/connecting-to-the-internet-with-pico-w.pdf

https://www.raspberrypi.com/documentation/microcontrollers/micropython.html

https://www.waveshare.com/wiki/Pico-ePaper-2.13

https://github.com/micropython/micropython-lib/tree/master/micropython

https://github.com/peterhinch/micropython-nano-gui

https://stackoverflow.com/questions/39534018/how-to-use-bom-api-for-weather-tide-and-swell

http://www.bom.gov.au/ntc/IDO59001/IDO59001_2024_VIC_TP027.xml


and learning micropython for embedded devices

making an e-ink tide chart



Commander

Clipboardy

Require vs import for diff versions

Couldn't I have just typed `cat /dev/random | base64 | head -c 8` into a terminal?

Yeah.

see: the time i posted my wifi password on github

password generator in node.js


I recently learned about testing when I succesfully deployed this blog, but with failed tests. It turned out the integrated tests were simply navigating to my website, and making sure the title could be read. Because if the title can be read and is correct, everything must be working right? Makes sense. Anyway my tests weren't passing because I changed the title of the website but didn't change the title the tests were looking for.

If you can use testing to navigate to a website and read it, what else can you do?

Thanks for asking, and yes you can use the magic of testing to nagivate to the Dominos pizza website, type in every possibile coupon code and report back which ones work.

For this little project I used Playwright, created to "enable reliable end-to-end testing for modern web apps."

#### Here's the code I've come up with:

```
import { test, expect } from '@playwright/test';

test('test', async ({ page }) => {
  await page.goto('https://www.dominos.com.au/');
  await page.getByRole('link', { name: 'Pick Up' }).click();
  await page.getByTestId('searchText.input').click();
  await page.getByTestId('searchText.input').fill('3000');
  await page.getByTestId('pickup-store-search.address.wrapper.carlton (vic)').getByTestId('pickup-store-search.address.name').click();
  await page.getByTestId('start-order-now-button').click();
  await page.getByTestId('cross').click();
  await page.getByTestId('basket-container.voucher-input.input.input').click();
  for (let i = 0; i <= 999999; i++) {
    const voucherCode = i.toString().padStart(6, '0');
    
    await page.getByTestId('basket-container.voucher-input.input.input').fill(voucherCode);
    await page.getByTestId('basket-container.voucher-input.input.input').press('Enter');
    await page.getByTestId('basket-container.voucher-input.input.input').press('Meta+a');
  }
  });
  ```
Similar to a person who forget his combination lock, the for loop tries every combination from 000000 to 999999, one by one.

####  Other important considerations

I've only run it testing from 000000 to 000010 because Dominos might catch on to what I'm doing and ban my IP address, then I'd have to learn to cook. So, running this script behind a VPS is probably a good idea, as well as adding some logic to make it take longer and randomise the time between attempts, so that theoretically my script might look like a really bored person manually typing coupon codes one after the other for hours on end.

Refer to React talk Cypress vs Playwright and Cypress testing in site

but the tests are 'what is every possible dominos coupon'

writing tests with playwright


lightnode turkey
tailscale curl -fsSL https://tailscale.com/install.sh | sh
configure exit node https://tailscale.com/kb/1103/exit-nodes?q=exit+node&tab=linux
mango router
appletv beta update and 
portainer
tailscale being added to tvos

but is it cheaper?

visiting my holiday home in turkey each weekend to watch formula 1


According to the TAC, "In the last five years, 55 bicycle riders have been killed on Victorian roads – an average of 11 each year." and "Killed in same direction crashes (40%)"

I was recently gifted a rear bike light with a camera built-in. Maybe it will catch the numberplate of the guy who kills me and drives off, or maybe it will just be fun to play with. Unfortunately the app it comes with isn't the greatest piece of UI design ever created, so here are some improvements I'd like to make to the overall experience.

To start with, to get recordings from the camera, you can either remove the micro-SD card and plug it into your computer, or connect to a wifi hotspot which is constantly broadcasting from the light whenever it's turned on and recording, and there's apparently no way to change the either the SSID or password.

Here are the improvements I'd like to make:

- [x] Stream from the camera without using the app
- [ ] Get previously recorded video from the camera without using the default app
- [ ] Change the default wifi config
- [ ] Make a better app (iOS only for now because I've never used Android.)
- [ ] Okay fine an Android app too, it can't be that hard (ref: [this post](/posts/robot-vacuum))

---

<h1>1. How does this thing work?</h1>
When connecting to the light's wifi network (CARDV_####), you're given a 192.168.1.# address.

nmap 192.168.1.1 gives me the following:


RTSP stands for Real-Time Streaming Protocol. VLC can open RTSP links. Unfortunately, there doesn't appear to be a way to find the exact link the camera is broadcasting from.

A few minutes of Googling default RTSP links for various dashcam models didn't yield any working results. But maybe the company will just tell me the link?

That was easy.

And... success! I can stream video to VLC on Mac or iPhone. So maybe the app is already created and it's just VLC? No, I still need a way to get previously recorded video from the camera.


---

<h1>Telnet</h1>

History of telnet at Bell Labs

Telnet description from Podcast:
If you had full access to a computer during your time slice, you didn’t need a punch card system, you could use a teletype terminal. Teletype terminals looked like large typewriters combined with printers and maybe a phone line, and they were originally used for sending telegraphs, I think. You could type in commands and send it directly to the computer using the telephone line and then have the results printed out right away right above you. And with a timeshare system, you could hook up a number of these to a single computer and split time between them.

Teletype terminals communicated over telnet, a protocol that’s still in use to this day, although I guess SSH has largely replaced it. The ASCII format of text documents was created for these teletype machines, and that’s why it has weird control characters like the end of the transmission. This was such an interesting time. It was the birth of these interactive computers. Anyways, back to the Multics project
ref: https://corecursive.com/brian-kernighan-unix-bell-labs1/

nmap listed a telnet port open. Let's see if it works?

But what's the username and password? root? nothing???

Yep.

A quick ls lists the following directories. And it looks like the micro-SD card is mounted at /mnt/mmc/

So I should be able to access photos and videos just like directly from the SD card at e.g. http://192.168.1.1/mnt/mmc/Normal/F/REC20240120-171923-1884.mp4

More success!


---

my bike light runs linux


1L PC
Installation
docker containers
Time Machine Time Capsule replacement
Homebridge upgrade (hue, sensibo, eufy, bravia)
Performance vs Raspberry Pi Zero W
bigger ssd in 1L pc

developer blog

my github contributions

add me on linkedin

writing a PDF cover letter in plaintext

making an e-ink tide chart

password generator in node.js

writing tests with playwright

visiting my holiday home in turkey each weekend to watch formula 1

my bike light runs linux

portainer home server

codecademy color design course

codecademy asynchronous javascript programming course

codecademy Javascript course

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codecademy Swift coßurse

codecademy Linux course

codecademy regular expressions course

codecademy Raspberry Pi course

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