Miscellaneous

One of these articles is not like the others.
One of these articles just doesn’t belong.

Sometimes a Robot Room article doesn’t fit in any of the other major categories that are used to navigate the website. When that happens, the article ends up here. In the event that enough articles merit a new category, they will disappear from here and move somewhere else.

Resistance sorting with Lego minifigures Minifigure Multimeter
Have you ever had a pile of assorted resistors that you wish to quickly organize? Place each resistor in the hands of the electrified Lego minifigure to see and hear the nearest standard resistance. This practical meter includes both an ohmmeter for resistance measurement as well as a voltmeter for battery measurement.
Pile of multimeters Multimeter Reviews
A digital meter is an essential tool for all robot builders and electronic hobbyists. If you’re just starting out, can you buy the least expensive model and still get accurate results? How much do you need to spend to get a decent mid-range model? A dozen multimeters are tested and compared.
Multimeter measuring resistance in ohm mode How to Measure Low Resistances
Occasionally you'll run across electronics such as relays, cables, igniters, switches, or current-sense resistors that have resistances less than one ohm. Few multimeters accurately measure less than 1 Ω, but most have a millivolt mode that can be combined with a 5 V source, a fixed resistor, and some simple math to determine milliohm resistances.
Broken probe tip thumbnail Replacing Broken Tip of IC Hook Probe
Arg! The multimeter measurements are wrong because the probe detached from the circuit because the IC hook tip broke, again! I go through far too many broken IC hooks to keep throwing them away. Is it possible to 3D print a replacement tip? Is this an opportunity to improve the tip to be more robust?
Leveling 3D Printer thumbnail Leveling A 3D Printer
How to accurately set the extruder nozzle height above the print bed when leveling a 3D printer. Use a thickness gauge, magnet, and a multimeter in continuity mode to beep when the print head makes contact. Includes a trick to clean the tip of the nozzle by scraping it with the zinc interior of a penny.
Polyester film capacitor Capacitor Leakage
When power is disconnected from a circuit, the capacitors on the board are discharged by the electronic components until no voltage remains. That’s fine. But, did you know that if you charge a capacitor on its own, it will slowly discharge through itself? More surprisingly, some capacitors become leakier with time, but can be healed through usage. I was shocked to discover how difficult self-discharge is to measure.
Faulty capacitors thumbnail Identifying Bad Capacitors
If your consumer electronic device is failing, it is often caused by old, overheated, or defective capacitors. If you open up the case and inspect the capacitors, you may find some that are bulging, crusty, or are lifting off the PCB. Here are some photographs of damaged CapXon brand aluminum-electrolytic capacitors found inside failing Samsung LCD monitors. Also included is a photo of a good capacitor that has beneficial goop surrounding it.
Camera mounted horizontally for overhead macro shot Macro Photography
Taking a picture of an electronic part, circuit board, or other small object is much easier if you have the right setup. This includes a DIY remote shutter release, desk lamp ring light, and horizontal tripod arm. Take a peek at the Robot Room digital camera setup.
Macroscope thumbnail Macro Photo vs Microscope
Fifteen years ago, I proudly photographed a PCB using an Intel QX3 toy microscope. How well does that old microscope compete against a modern 16 megapixel camera with macro lens, extension tubes, tripod, linear table, linear slide, remote shutter, 28 LED ring light, and stacked photography software? Can such a photo setup match the microscope's 200x magnification? In fact, exactly small of details can we clearly see with a modern rig? Would you believe 10 µm?
Desk mount tablet arm for YouTube videos thumbnail Mounting an iPad for Desk-Based YouTube Videos
For many hobbies, an overhead shot of your desk or workbench is the ideal view for your videos. This is unwieldy for tripods, but suitable for a desk swing arm. Similar to a desk-mounted magnifier light, the camera can be quickly positioned at various distances, and can be swung away when not in use. The single arm does not tend to block room lighting. Take a look at my tablet-mount setup, and see how the arms were extended to fit a larger form factor.
A lovely and all-too-common washed-out flash photo. Safe Sync for External Flash
Digital cameras have a relatively low voltage limit on their sync hot shoe, compared to mechanical cameras. This makes modern cameras susceptible to damage from higher-voltage external flash units, which consumers and hobbyists may attempt to reuse from previous generations. The circuit described in this article is a classic solid-state level-shifter often used to interface DC circuits to AC appliances.
Parachute and rocket nose cone sticking out of a tree branch How to Get a Model Rocket Out of a Tree
Oh no! A rocket has gotten stuck in a tree branch approximately 36 feet off the ground. How can it be rescued? With bamboo poles? A novelty party balloon with fishing line? Or a coat hanger hook with a boring conventional ladder? Find out!
thumbnail of a Lego astronaut before being lost in space Repairing a Model Rocket
A rocket found in a tree had loose and missing fins, a broken parachute, and a lifeless shock cord. Replacement fins can be made from balsa wood, using a pen and a hobby knife. After sanding, they can be reattached with two kinds of glue. Simple repairs and replacements make the rocket flight capable again. After all that work, an overzealous choice of a rocket motor sealed the rocket’s fate. Where do you think the rocket (and “Lego Major Tom”) ended up?
Walled-in playing field for a robot contest Building a Robot Contest Arena
Constructing a playing field for robots is much harder than it seems. Here are some tips for cutting wood boards, machining retention lips for scoring areas, chiseling notches, connecting wall together, and filling gaps.
Error Correcting Code thumbnail Hamming ECC
Error correcting code (ECC) is superior to ordinary checksums, in that is can both detect and correct errors in data storage and transmission. Learn how Hamming codes work. Fully working C library included.

DAC is a hexadecimal number Digital Number Systems
Whether you’re working on robots, digital circuits, software, or microcontrollers, you'll encounter numbers that aren’t decimal. This tells you how to convert a number to and from hexadecimal, binary, octal, and decimal.
Brian Damaged Safety Signs
Whether you are a fan of slapstick or just have secret schadenfreude, these are standardized workplace signs that are amazing effective at grabbing your attention so that a piece of equipment doesn’t grab you.
Storm Impact logo Storm Impact
Before there was Robot Room, David Cook authored a number of video games and utilities for the Apple Macintosh computers, such as TaskMaker, MacSki, Asterbamm, Tomb of the TaskMaker, and Technical Snapshot.