Panel Meter-To-Bluetooth Hack Hijacks The Display Segments

There are a proliferation of cheap digital meter modules available online for pocket money prices. Current, voltage, frequency, or combinations thereof can all be yours for just a few dollars and a wait for shipping. Unfortunately though these meters are all self-contained units. They do not have a serial port or other interface through which you can log their readings.

This failing was not an obstacle for [Scott Harden], though. He simply added a Bluetooth interface to his combined voltage and current meter module by using an ATmega328 microcontroller to capture the signals sent to the module’s display LEDs and interpret them into readings for his Bluetooth module. He details the process of reverse engineering the meter, and his build. The result is an intriguing mess of wires with a DIP ATmega hanging on their ends. But it performs the task requested of it admirably and when mounted in a project box you would not know what lurks within.

He has made his code for the project available in his GitHub repository, we can see that this could be a valuable technique for use with other similar displays. In the video below the break he gives us a full run-down, as if his comprehensive write-up was not enough.

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Building a crystal oven

Radio communications depend on stable oscillator frequencies and with that in mind, [Scott Harden] built a module to regulate temperature of a crystal oscillator. The process is outlined in the video after the break but it goes something like this: A small square of double-sided copper-clad board is used as a base. The body of the crystal oscillator is mounted on one side of this base. On the other side there is a mosfet and a thermister. The resistance of the thermister turns the mosfet on and off in an attempt to maintain a steady temperature.

This is the first iteration of [Scott’s] crystal oven. It’s being designed for use outdoors, as his indoor setup uses a styrofoam box to insulate the oscillator from ambient temperatures. He’s already working on a second version, and mentioned the incorporation of a Wheatstone bridge but we’ll have to wait to get more details.

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