A Voice Activated Light Switch

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

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”.

Schematics and board design files are available on the github project page.

Analog Computing: Shortest Path

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!

References and additional reading:

Description Reference
Maze solving with helium gas Glow discharge in microfluidic chips for visible analog
computing
, Darwin R. Reyes, Moustafa M. Ghanem, George M. Whitesides and Andreas Manz, Harvard University
Maze solving with hexyldecanoic acid Maze Solving Using Fatty Acid Chemistry, Kohta Suzuno, Istvan Lagzi, et al
Bob Pease on analog computers What’s All This Analog Computing Stuff, Anyhow?, The Bob Pease Show
Analog computing lecture High performance/low power computing based on the analog computing paradigm, Bernd Ulmann, SIGINT 2013
Classic text on analog computers Electronic Analog Computers, Granino & Theresa Korn

MHS-5200A Teardown and Review

After seeing WD5GNR‘s excellent work on reverse engineering the serial protocol for the cheap ebay MHS-5200A arbitrary function generators, I decided to pick one up as a secondary function generator for the lab.

What started as a simple review and teardown video ended with me reverse engineering the entire analog front end to track down the source of some nasty harmonic distortion!

MHS-5200A channel 1 analog front end

MHS-5200A channel 1 analog front end

Why My Thermometer Circuit Sucks (And How to Fix It)

Although the ammeter thermometer circuit described in my previous post works, it doesn’t work well, and in general is poorly engineered.

Let’s make a critical examination of the existing circuit, and re-design it to be:

  • More accurate
  • Over a wider temperature range
  • Using less expensive components
  • While drawing less current
  • With a faster response to ambient temperature changes
New analog thermometer schematic

New analog thermometer schematic

A Microammeter Thermometer

I wanted to familiarize myself with Microchip’s MCP9700 thermistor ICs for some upcoming projects that require temperature measurement / compensation.

I decided to build a simple circuit around the MCP9700 to convert an old analog micro-ammeter into a thermometer for the lab. It displays 1uA per degree Celsius, has an output of 1mV per degree Celsius for external temperature monitoring / data logging, and draws only 20uA from a 5V supply.

The analog thermometer reading 20 degrees Celsius in the lab

The analog thermometer reading 20 degrees Celsius in the lab

Not only is it a cool looking centerpiece (I’ve always found old analog meters absolutely beautiful), it’s quite useful too!

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Building the Widlar Hassler

One of my personal favorite Bob Widlar pranks was his “hassler” circuit, which he used to combat office noise.

If you spoke too loudly in the presence of the hassler, it would emit a high pitch tone, which would decrease in frequency the louder you spoke; this had the effect of causing an annoying ringing noise in your ears. As soon as you noticed the ringing and stopped talking in order to identify the source, the hassler would shut up too.

The Widlar salute!

The Widlar salute!

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Building an RF Power Meter

Here is yet another AD8307 based RF power meter which adds an opamp to produce a DC output voltage of 1mV/dBm (e.g., 0mV = 0dBm, -10mV = -10dBm, etc). The RF power in dBm can be read directly with a multimeter, and I’ve found it particularly useful for measuring RF filter response when combined with a sweep generator and an oscilloscope:

Visualizing a 6MHz Low Pass Filter Response over 1-11MHz (10dBm/div)

Visualizing a 6MHz Low Pass Filter Response over 1-11MHz (10dBm/div)

The AD8307’s high dynamic range and good accuracy over a wide bandwidth make it especially useful if, like me, you don’t own a spectrum analyzer which would otherwise be ideal for filter measurements.

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