Build fun circuits! Impress your friends! (Or at least the ones who aren’t in-the-know ðŸ˜‰ )

With some inspiration from The Fifth Element and Iron Man, here’s a voice-activated light switch that provides the illusion of a more advanced artificial intelligence, with the simplicity of “the clapper”.

I’ve gotten a lot of questions on the blog about the new version of the MHS5200A function generators available on eBay. Viewer Tolga was kind enough to send one in to me to review and tear down. Although some improvements have been made over the older models, there are some concerning issues with these new models too!

I recently designed an infrared sensor board (dubbed “IRis”) for my friend’sDefcon talk. This video walks through the circuit design of the photodiode amplifier, and discusses some of the pitfalls associated with photodiode amplifier design.

Schematics, BOM, and KiCAD design files for the described IRis board are available on github.

Need a frequency doubler? Want to plot a cubic function on your ‘scope? How about a square root extractor, or a voltage controlled amplifier? Analog multipliers make all this (and more) a snap!

Ever tried searching through your datasheets for the motional parameters of that quartz crystal you just bought? Good luck! Vendors simply don’t specify these parameters to general end users, and for most applications that’s OK. But for high Q oscillator and filter design, measuring and matching crystals can be important.

This video discusses crystal motional parameters, how to measure them with a crystal impedance meter, and finally examines the measured values of 150+ real world crystals.

Below are some interesting correlations/statistics gathered from the measured data; raw measurement data is available here.

Average C0 capacitance for each crystal holder type

Average motional resistance vs frequency

Average motional inductance vs frequency

Average unloaded Q vs frequency

Average unloaded Q for each crystal holder type

Unloaded Q of glass-sealed crystals vs average unloaded Q

Overall statistical analysis of unloaded crystal Qs

References and additional reading:

Description

Reference

Crystal motional parameters and relevant equations

Inspired by Micah Scott’s recent tweets on analog computing and maze solvers, here is an analog computer that solves the shortest path between two points in multi-path maze. All you need are some LEDs and a current source!

Its hard to beat the cost and versatility of the ubiquitous RTL-SDR dongles, but the temperature stability of their reference oscillators isn’t sufficient for some applications. While the internal 28.8MHz quartz crystal in these units can be replaced by a high qualitytemperature compensatedoscillator, these tend to be relatively expensive and/or difficult to source.

Here’s a scratch-built 28.8MHz TCXO capable of +-1ppm stability from 0C-55C; best of all, it’s not only easy to build, but is designed entirely from readily available and inexpensive components. For improved temperature stability, the main oscillator can even be replaced with one of many commercially available TCXOs!

UPDATE: Elia has kindly designed a PCB for this circuit, using a commercially available TCXO. Now available from OSHPark!

KiCAD schematics and additional project files are available on github.

Today we explore the use of oscillator synthesis software (Genesys) for practical crystal oscillator design, and the impact of the Randall-Hock correction formula on linear open loop analysis accuracy.

Here’s an inexpensive precision peak detector circuit that accurately tracks the peak voltage of input signals at frequencies up to 100kHz and has zero voltage droop over an indefinite period of time…no microcontrollers required!

The following circuit uses a dual comparator, three op amps, and a digital potentiometer to provide two peak detection outputs: one “real-time” peak output, accurate to within 2% for input signals up to 100kHz, and one maximum peak output which outputs the maximum peak voltage seen since the last reset: