List page: Electronics

Modifying a radiation meter for (radioactive) rock collecting:

The Ludlum Model 3 is quite a nice radiation meter, as long as you like analog displays and don’t mind it weighing one and a half kilograms:

Building a metal detector

The bucket brigade device: An analog shift register

Nowadays, digitally delaying audio is easy, but historically we had to use devices like the TCA350, a fully analog delay line:

Building a fluxgate magnetometer

Magnetic materials, like iron and ferrite, limit how much magnetic flux can pass through them. Normally, they concentrate nearby magnetic fields, but at the limit — in saturation — they exclude them.

Fixing the CH341A/B based flash reader:

CH341B and CH341A based “MiniProgrammer” boards are by far the most common low cost flash programmers. They’re able to read and write from most SPI and I2C flash chips, often while the chip is still connected to its circuit.

Making a rickroll laser: A parametric speaker.

Most speakers emit sound in all directions because they are relatively small compared to the wavelength. Audible sounds have wavelengths of up to several meters, so an acoustically “large” speaker might not even fit in your house.

Getting gigahertz from two 1N4148s

Let’s make harmonics, lots of harmonics. This can generate evenly spaced carriers for testing receivers, and create high frequency signals referenced to a stable, low frequency reference.

Inside a 1 dollar radar motion sensor

I recently got some cheap RCWL-0516 microwave motion sensors, mostly because I was wondering how China managed to make a radar for under a dollar:

Making a simple ionization chamber radiation detector:

To build the ion chamber, I soldered some wire to a steel can as one electrode, drilled a hole in the closed end and inserted another wire as the other electrode. I then covered the opening with metal mesh to keep out static and stray fingers. Aluminum foil can be used for better shielding from static electricity, but at the cost of blocking alpha particles from entering¹.

How (ionization) smoke detectors actually work:

Most sources describe smoke detectors as using an ion chamber, with a strong alpha source inside. The alpha radiation ionizes the air inside the chamber, creating a small current flow, measured by the detector. When smoke enters through vents in chamber, it blocks the alpha particles, reducing the current and activating the alarm. A video on the Wikipedia article even gives a rough schematic¹:

Building a crude bolometer, or the world's worst thermal camera.

A bolometer detects the heat from absorbing light. This comes with limits sensitivity and speed, but works at wavelengths which are very difficult to detect, like thermal infrared.¹

Generating a spectrum from the PIN diode X-ray detector.

The pulse shaping amplifier outputs short pulses with around 10 mV/keV:

.2 ms/50 mV per division

These pulses have a similar amplitude to audio from a microphone preamp, so they can be digitized by feeding them into a computer’s soundcard. If the computer has dedicated audio input, connect the circuit as the headset microphone using a TRRS plug. Generally, the sleeve is ground, and the ring next to it is the microphone signal. The soundcard will apply a bias voltage to power the microphone, so add a 1 uF MLCC DC blocking capacitor.

Cleaning up the signal from the PIN X-ray detector

Yesterday, we demonstrated detecting soft X-rays using a BPW-34 PIN photodiode, and a charge sensitive preamplifier. Unlike a conventional G-M tube, the photodiode can measure the energy/wavelength of X-ray photons, which is characteristic of the source. However, the raw output from the preamplifier is not very usable; It is very weak, noisy and the pulses have long tails:

(Ab)using PIN photodiodes as soft X-ray detectors

PIN photodiodes are diodes with a thick undopped/intrinsic layer between the P and N-type regions. This layer is typically around .1 mm, creating a similarly thick depletion layer. When light shines into the depletion layer it liberates electron-hole pairs, which, if reverse biased drift into the dopped regions, allowing a small current to flow.

Counting with neon

Neon lamps have a unusual property; When the striking voltage, typically around 90 volts, is applied, the neon inside ionizes and begins to conduct, creating a nice orange glow. Once ionized, a lower voltage is required to keep the neon glowing, typically around 60% of the striking voltage, the maintaining voltage. This is why they always need a series resistor, to prevent them from drawing a huge amount of current once they light.

How semiconductors actually work.

In an atom, most electrons sit deep inside, but some, the valence electrons (up to 18) are on the outermost shell and able to interact with the world. These are the electrons that form bonds with other atoms, interact with light and do other intresting things. However, in most materials, these electrons are still bound to their respective atoms and molecules. While it is possible to get these electrons moving, this requires so much force it often destroys the material (and starts a fire).

Testing PCB ground plane myths

Basically everyone agrees that a ground plane provides a low inductance and low resistance return path for current, and prevents crosstalk/coupling between traces.

Magically slowing down signals with sampling.

Mixers are the classic way to convert a signal to a lower frequency so it can be processed or measured easier. But mixing only works on narrowband signals, ones that are very nearly a sine wave.

Making logic gates with "transformers"

The normal way to get an LC tank circuit to oscillate is by using an amplifier to apply positive feedback. However, it can also oscillate if the inductance or capacitance is changed at twice the resonant frequency (parametric oscillation). ¹ (This is going somewhere, I promise)

Modulating and amplifying signals with (electro)magnets.

This is a functional AM modulator (and with the help of a rectifier, an amplifier) built entirely out of transformers and inductors:

A simple wireless power demonstration circuit

The core principal behind most wireless power systems is electromagnetic induction, where current flowing through a coil generates a magnetic field, and a magnetic field generates current in a coil.

Using a neon bulb as a light sensor (and other fun configurations)

Neon lamps, small gas discharge tubes used as indicator lights, have fairly interesting electrical properties. Until a certain voltage is reached, the striking voltage (around 90 V for most), the lamp conducts nearly no current. Once the striking voltage is reached, the gas inside the lamp ionizes, allowing current to flow much easier. Current flows so easily, that if maintained at the striking voltage, the lamp would ark over and quickly overheat. Neon indicator lamps require driver circuitry to avoid this, and for small, low power, indicator lamps, this can be as simple as a resistor.