Tag Archives: DIY

Build your own HF balun

via Dangerous Prototypes

Miguel, EA4EOZ, posted this great DIY tutorial on building your own balun:

A balun is a MUST for dipoles or similar antennas when they are feed with coaxial cables. Many hams connect the center conductor of the coaxial cable to one side of the dipole, and the shield to the other. Wrong!
From the RF point of view, the shield can be modeled as two conductors, the internal shield (the real shield, this is, ground) and the external shield, who is really far to be ground. In this way, your dipole has 3 arms, the two from the dipole and the coaxial cable shield (external face).

See the full post on EA4EOZ blog.

DIY OpenDPS power supply

via Dangerous Prototypes

Evan’s DIY OpenDPS power supply:

Years ago I heard about the OpenDPS project to give open source firmware to cheap and available chinese power supplies. These aren’t strictly whole power supplies, they are configurable CC and CV buck converters. That means that it needs a stable DC source to back it to be used as a bench power supply. Perhaps you may not want to do this if you intend to use the DPS as a battery charger run from a solar supply or something, but most people I see want to use them for bench supplies so that requires an existing DC supply. Today I finally finished mine.

(Not a) triple tube geiger counter

via Dangerous Prototypes

Doz’ triple tube geiger counter project, that is available on GitHub:

So, two little switching power supplies, one for the DOB-50 and CTC-5 as they have similar operating voltages, and one higher voltage one for the DOB-80, a simple op-amp comparator to output the pulses to an Arduino to process and display the results.
The power supplies are controlled using two MC3406AD’s, driving an IRF840. I’ll just refer to the component numbers on the top supply, the bottom one is almost identical. The back EMF from the inductor L2 is rectified by a UF4007. There’s a feed back loop, R14,15 & 16 and the pot is used to adjust the HT..

More details on Doz’ blog.

Check out the video after the break.

100 MHz third overtone crystal oscillator

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100 MHz third overtone crystal oscillator @ DIYfan:

Couple of years ago I purchased from a local store 100 MHz crystal resonator and tried several times to make a working schematic on breadboard using standard circuits I found on the internet. It never worked good enough, usually oscillating at 33.3 MHz instead of 100 MHz. Finally, I found that the crystal is third overtone type.

Low cost Carbon Monoxide meter

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Dilshan has published a new build:

Today Carbon Monoxide (CO) meters are available in different forms. Overall, Carbon Monoxide meters sense CO fast and display the amount to the user and trigger alarm if it reaches a critical level. Compare with most of the DIY Carbon Monoxide meters, the project which we described in this article does not need any development platform or MCU / firmware. The Carbon Monoxide meter in this project design around using general-purpose ICs, such as NE556 and LM3914.

More details on Jayakody’s Web Log.

Check out the video after the break.