Juan's Projects

Just a simple BFO (beat frequency oscilator) metal detector based on  this one . It is comprised by two LC oscillators, a fixed or reference one and a search one. The coil of the search oscillator is located in close proximity to the ground. When a metal object is close, it changes the inductance of the coil, changing the frequency the search oscillator works at. In this case, both oscillators work around 200 kHz. Both signals are added together, and that results in an AM signal, which can be demodulated. The audio tone resultant happens to be the difference of the two frequencies. This way, changes in frequency of the search oscillator can be noticed as the sound frequency changes. Testing and modification of the original design. Notice that AM signal and its demodulation can be seen on the scope: The frequency adjustment was modified and an audio amplifier was added. Here is the schematic for my version. Capacitor values are marked as they appear on the physical com...

The plastic coupling connecting the delayed sweep knob with its potentiometer was cracked, and after trying to glue it (it refuses, seems to be some kind of polyethylene), I just 3d printed a replacement. Now I can use the 'scope to its full extent.

This is my third attempt at building an RC submarine, a difficult endeavour as those who have had a go at it will know. After a German WWII U-Boot (undergoing repairs), and a Russian Akula (decommissioned two years ago), now it was time for a Spanish one. The S-80 class submarines, still under construction, have been elongated due to technical problems. This model, at 1:120 scale, is of the original project. The hull was modelled in Fusion 360 using photographs found online and some rather vague lateral and top views found on related publications. Then, it was 3d printed in grey ABS and acetone-welded together.  The WTC, housing all the control electronics, servos, pumps, and propulsion motor is made out off a convenient water bottle I found at a local shop. Anyone wishing to replicate this project will have to find a suitable container. All movements are magnetically coupled to the exterior, and two tubes go out through the end cap, one housing the antenna a...

Just bought a second-hand Hameg HM604. It just needed some calibration and fixing a broken rod coupler to get it up an running. Here are some photographs of the inside should anyone find them useful. I didn't get into the volts/div switches, as the metal cans they are in are welded shut. Some photos of those can be found in this  EEVBlog thread. Anyway, here are some more photos:

This is a USB Polygraph, which I designed and built as a classroom project on June 2018. The hardware side is pretty simple, an Arduino UNO collects data from some sensors and sends it via serial. On the computer, a Python program takes that data and not only graphs it, but it also allows the user to save it, manages questions and adds question and answer markers to the graphs so results can later be inspected. All results are saved in .txt files. First, some legal stuff: DISCLAIMER: I make no claim whatsoever on the validity of poligraphy for lie detection. Call this a signal acquisition device if you must. While it makes for an interesting and enjoyable build, it is intended just as an experiment and cannot distinguish between truth or else. Anyway, it is up to the user to decide. Always make use of common sense. WARNING: Using this device involves attaching metal objects to someone's hand. To avoid any possibility of shock hazard, please make sure all "probes" ...

This is a dual channel linear lab power supply I have spent recent months building, much thanks to the help received in  this EEVBlog thread . All design files are available in this  GitHub repository . I will attempt to go over the general progress of the project, but please refer to the said thread for more information. Design requirements: Dual isolated channels. Adjustable voltage and current  30 V , 500 mA per channel. Digital voltage and current displays. Build stages: First, the case was made out of a wooden board and 3d printed front and back panels. Heatsinks were taken from old computers. One side of a 2x 10Vac and a 15 Vac transformer power each channel, plus a 12 Vac smaller transformer for the displays, fan and microcontroller. Ac voltages are rectified and filtered on a separate board. Here are some photos of the early development, initial circuit was based on the one found  here . Then came perfboard prototypes, testing and thr...