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
At its simplest, a bolometer is simply a black object attached to a heat sensor, both somewhat isolated from the surroundings. Typically a thermistor is used as the heat sensor, but I did not have any on hand, so I used a 1N4148 silicon diode.
(Electronics)
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.
(Electronics)
(Ionizing radiation)
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:
10 keV X-ray. 1 mV/1 ms per division. (It’s hidden by an aggressive bandwith limit, but there is 2 mV RMS noise here.
(Electronics)
(Ionizing radiation)
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.
X-rays: An X-ray photon1 can also knock an electron free, but the excess energy causes it fly trough the semiconductor, knocking more electrons free:
(Electronics)
(Ionizing radiation)
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.
(Electronics)
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).
(Electronics)
Basically everyone agrees that a ground plane provides a low inductance and low resistance return path for current, and prevents crosstalk/coupling between traces.
A ground plane does this by providing a return path1 for current that is physically close to the trace. Inductance and inductive coupling depend of the area of the loop formed, which minimized by a ground plane. With capacitive coupling, the ground plane “shorts” the electric field between traces, minimizing mutual capacitance.
(Electronics)
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.
Sampling can slow down any repeating signal, including square waves and narrow pulses. The trick is to measure the voltage at a slightly lower frequency then the signal’s repetition rate, and hold that voltage until the next measurement.
(Electronics)
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)
The capacitance can be changed using a varactor diode, but, more exotically the inductance can be changed by driving the core into saturation with another winding:
(Electronics)
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.
Induction can be used to transfer power wirelessly by placing 2 coils next to each other; When alternating current is applied to one coil, it creates an alternating magnetic field, some of which then passes through the other coil, creating an electrical current in the coil:
(Electronics)
(Wireless communication and power)
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.
(Electronics)