DIY Grid Dip Meter Teardown

January 7, 2026 by No comments

You don’t see them much anymore, but there was a time when any hobbyist who dealt with RF probably had a grid dip meter. The idea was to have an oscillator and measure the grid current as it coupled to external circuits. At resonance, the grid current would go down or dip, hence the name. In the hands of someone who knew how to use it, the meter could measure inductance, capacitance, tuned circuits, antennas, and more. [Thomas] takes a peek inside a homebrew unit from the 1950s in a recent video you can see below.

These meters often have a few things in common. They usually have a plug-in coil near the top and a big tuning capacitor. Of course, there’s also a meter. You have to pick the right coil for the frequency of interest, which both sets the oscillator frequency range and couples to the circuit under test.

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Graphing Calculator Gets USB-C Upgrade

January 7, 2026 by 6 Comments

Unlike Texas Instruments, whose graphing calculators have famously not made technological improvements in decades despite keeping the same price tag, HP has made a few more modern graphing calculators in the last few years. One of which is the HP Prime which boasts hardware from the mid-2010s including an ARM processor, a color screen, and rechargeable lithium battery. But despite this updated hardware it’s still using micro-USB for data and charging. [David] wanted to fix that by giving this calculator a USB-C port.

The first steps were disassembling the calculator case and removing the micro-USB port. The PCB is glued to the LCD screen which isn’t ideal, but he was able to work on it with everything attached. The parts are small enough to need a microscope, and with a hot air station he was quickly able to remove the USB port. His replacements from a generic online retailer were able to be soldered without much effort, but there was one major complication. The new USB-C ports didn’t account for the “On The Go” mode supported by micro-USB and were shorting a pin to ground which put the calculator into “host” mode instead of acting as a device. But using the microscope and cutting a trace on the PCB disabled this mode permanently and got the calculator working properly.

As far as modernizing calculators go, it seems like the HP Prime checks a lot of boxes, with the major downside that the LCD screen and more powerful processor means that the battery needs to be charged more often than the old TI calculators. Rather than carry a dongle around everywhere, [David] found this to be a much more efficient change to his trusty HP. If you’re still stuck using TI calculators, though, there are a few ways to modernize those as well like this build which adds a lithium battery or this one which ports a few Game Boy games to the platform.

A man's gloved hand is need adjusting the valve on a cylinder, from which a clear plastic tube extends. The man's other hand is seen holding the the other end of the tube in front of a dish of burning wax, which is flaring brightly.

Testing Laughing Gas For Rocket Propellant

January 7, 2026 by 10 Comments

Nitrous oxide’s high-speed abilities don’t end with racing cars, as it’s a powerful enough oxidizer to be a practical component of rocket propellant. Since [Markus Bindhammer] is building a hybrid rocket engine, in his most recent video he built and tested a convenient nitrous oxide dispenser.

The most commercially available form of nitrous oxide is as a propellant for whipped cream, for which it is sold as “cream chargers,” basically small cartridges of nitrous oxide which fit into cream dispensers. Each cartridge holds about eight grams of gas, or four liters at standard temperature and pressure. To use these, [Markus] bought a cream dispenser and disassembled it for the cartridge fittings, made an aluminium adapter from those fittings to a quarter-inch pipe, and installed a valve. As a quick test, he fitted a canister in, attached it to a hose, lit some paraffin firelighter, and directed a stream of nitrous oxide at it, upon which it burned much more brightly and aggressively.

It’s not its most well-known attribute in popular culture, but nitrous oxide’s oxidizing potential is behind most of its use by hackers, whether in racing or in rocketry. [Markus] is no stranger to working with nitrogen oxides, including the much more aggressively oxidizing nitrogen dioxide.

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How Do PAL And NTSC Really Work?

January 7, 2026 by 13 Comments

Many projects on these pages do clever things with video. Whether it’s digital or analogue, it’s certain our community can push a humble microcontroller to the limit of its capability. But sometimes the terminology is a little casually applied, and in particular with video there’s an obvious example. We say “PAL”, or “NTSC” to refer to any composite video signal, and perhaps it’s time to delve beyond that into the colour systems those letters convey.

Know Your Sub-carriers From Your Sync Pulses