Add blog post about MagTag satellite pass project

_posts/2026-08-26-sat-magtag.md

@@ -0,0 +1,43 @@
+---
+layout: post
+title: "MagTag Sketch for Satellite Passes"
+date: 2026-08-26
+---
+
+This is too cool not to share!
+
+At this past weekend's RMHAM Summer Swapfest, I acquired a couple of e-ink display gadgets with
+ESP32 microcontrollers without knowing exactly what they were. I figured that, at worst, they would
+be cheap Chinese Arduino-compatible devices that would be clunky but possible to program. Once I got
+them home and was able to research them properly, I discovered they were
+[Adafruit MagTags](https://www.adafruit.com/product/4800)!
+
+Being Adafruit products running CircuitPython, these boards came batteries included (figuratively,
+but also literally) with great documentation and support! It was quick and easy to get them loaded
+with the baseline bootloader and CircuitPython firmware, and then start experimenting with test
+sketches that ping Google and the like.
+
+With a baseline established, I went searching and found the excellent
+[N2YO.com API](https://www.n2yo.com/api/) for AMSAT and other orbital objects. The great thing about
+it is that, in addition to providing fresh, raw
+[TLEs](https://en.wikipedia.org/wiki/Two-line_element_set), it can also provide pre-crunched pass
+information given the observer's location. This is huge because it means I don't have to do orbital
+math on a puny microcontroller! I can query each satellite I'm interested in, sort them all by the
+Acquisition of Signal (AOS) time, and throw them on the display.
+
+![Basic MagTag display](/assets/2026-08-26-magtag-basic.jpg)
+
+I started out simple, having the device wake up once an hour and update the display. Once that was
+working, I got a bit fancier and started highlighting current passes and graying out recent passes
+closer to real time. This required caching my N2YO queries because I was using up my API quota. As
+it turns out, when you're querying six satellites on every run and making code changes that cause
+the program to run every few minutes, it's rather easy to blow through 100 queries in an hour and
+get rate-limited! I also added a low battery mode to make the display show when the gadget needs to
+be recharged instead of just displaying stale data forever.
+
+![Active MagTag display](/assets/2026-08-26-magtag-active.jpg)
+![Recent MagTag display](/assets/2026-08-26-magtag-recent.jpg)
+
+Overall, I'm quite happy with this very functional new gadget I have to keep me aware of AMSAT
+opportunities. Check out the
+[MagTag Sketch for Satellite Passes](https://github.com/xylo04/magtag/tree/main/sat-passes).

resize-images.sh

@@ -1,4 +1,10 @@
 #!/usr/bin/env bash
+
+if ! command -v convert >/dev/null 2>&1; then
+  echo "Error: 'convert' is required. Install ImageMagick and try again." >&2
+  exit 1
+fi
+
 max_dimension=1024
 images=$(find assets/ -iname "*.gif" -o -iname "*.png" -o -iname "*.jpg" -o -iname "*.webp" | sort)
 for i in $images; do