Chasing a Voltage Ghost

Breadboard power supplies cost less than a dollar on AliExpress. They are quite convenient for quickly powering and prototyping microprocessor circuits, Arduino projects with sketches, USB-powered prototypes, and on. The imagination is the limit. I spent the morning trying to figure out why my MB102 breadboard power supply was outputting only 3.5V, not the expected 5.0V.

Cluster Computing – Benchmarking Local Storage

Given a cluster computing rig of twenty-eight processors, each can have either a USB 2.0 or microSD local flash storage. Which type of flash and maker is the fastest? Make the wrong choice and the cluster is painfully slow. Not all microSD cards or USB drives are made the same, and interestingly random read and write speeds vary wildly. Here I test several storage configurations with striking benchmark results.

Experience with Inexpensive MicroSD Cards

For the cluster computing project I’m working on, I need 28 microSD cards. There was an AliExpress sale with good reviews, so I ordered a batch of 30 microSD cards, and at a great price point at the time. As long as the cards are Class 10 and work then we should be good, right? Results: Half are fake or defective. The rest are painfully slow. No refunds.

Cleaning Raw Candle Data for Time Series Analysis

Problem: How to clean the raw OHLCV candle data from the broker for time series analysis? Suppose we have an autonomous program that prioritizes and continually downloads the latest minute and day candles, as well as periodically gets new symbols from the broker. The problem is that the candles are not guaranteed to be full-period […]

Automated Web Testing with PHP and Selenium

Things break. Just the other day through a series of seemingly unrelated events, a new Microsoft x509 certificate made its way into a security handshake process which went unnoticed until current single sign-on sessions began to expire. Had we also had automated security testing, we would have caught this one-off. I’ll explain how I set […]

Algorithm: Optimized PDF Web Page Print Layout

I’d like to share my efforts to prevent page breaks in the middle of paragraphs and maximize the use of page space when printing web pages to PDF. I’ll outline how this PHP+NodeJS+Chrome tool and algorithm accomplish this. The motivation is to prevent pictures from being cut off, cut halfway through, or from being pushed […]

GoAccess Web Log Analyzer Installation on CentOS

GoAccess web log analyzer is a beautiful tool to show real-time traffic and stats – including GeoIP information, bandwidth usage, and visitor time distributions – of my web projects and apps over and above Google’s Webmaster Tools and UA reporting. At a glance I can see current traffic and historic traffic just by adding a […]

Download YouTube 4K Videos with PHP and SlimerJS

Among friends let’s agree we’ll be privately caching videos and not permanently saving them, or we’ll be using them for Fair Use, and we’ll certainly not upload nor share these videos outside of the originating platform (e.g. YouTube.com). Existing YouTube downloader scripts: YouTube-Downloader (does not work with videos using a cipher signature) YouTube video downloader […]

Running Xvfb on a RHEL Shared Host (without X)

This is how I compiled the Xorg Server for RHEL on a CentOS machine with modifications to create a portable Xvfb binary. Xvfb (X virtual framebuffer) is an in-memory display server for Linux and Unix-like OSes. It enables running graphical applications without a display such as running a headless browser (e.g. A full-blown Firefox instance […]

Bungee Jumping in Japan

That was really a really high bridge – 70m – and the river was shallow beneath us. There was no one else there. The team of jump masters was ready for just us two. It was amazing, like we had the whole valley to ourselves, Alex and I. We wanted an adventure, something we’d never […]

PhpStorm Productivity Shortcuts

I use PHPStorm daily and it’s nice to remember the shortcuts. Sitepoint has a great run down of productivity shortcuts. I’m reproducing my favorite ones here. This comes straight from Sitepoint. PhpStorm remembers multiple clipboard contents – you can press CTRL+SHIFT+V to summon a popup which lets you paste clipboard content that’s less recent than […]

Hello world!

Welcome! I usually keep my writing in my source code comments, or in Evernote, or on Stackoverflow.com, but it makes sense to keep my most useful snippets and research in one central place. This site is more for my own reference, but enjoy if something here helps you.