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Dan Gravatt

Dan's Articles

The Retro PIC Single-Board Computer
January 2017
Put some of your historic chips to work in a new “computer” system with a PIC acting as the CPU.

Flight Computers for Sounding Rockets
January 2015
Sure, launching model rockets is cool and all, but what if you could incorporate some science and learning into the fun, too. The flight computers described here will help you do that.

The (Nearly) Universal Process Monitor
January 2014
While the circuit described here is specifically for showing system parameters in an electric truck conversion, you can utilize it as a process monitor and display for analog and pulsed signals in a variety of applications.

Hacking the Nine-LED Flashlight
April 2013
The simple circuit in these now common flashlights actually eats through batteries pretty fast. This hack adapts the flashlight to use an external power source, and adds a pulsed driver circuit for better efficiency.

Build the Alarm Autodialer
August 2012
This device will detect and report several common failures with household systems, so you can deal with them while they are still easy to fix. It's inexpensive ($60 or less, depending on your parts collection), easy to build, and doesn't require any contracts with monitoring services.

Build the Pi Scrolling Display
July 2012
This versatile display lets you have your pi and see it too! With 15 available digits, you can also use it to create your own desktop National Debt clock.

True-Reading Automobile Gas Gauge
April 2011
Finally, here’s a device that can tell you exactly what your fuel level is.

Make the PLL Frequency Synthesizer with PIC Control
September 2010
This project describes how to build a frequency synthesizer — a device which generates a stable waveform at a user-selected frequency. Frequency synthesizers are handy test instruments for digital circuits, and can also be used for audio signal generators or radio frequency mixing applications. This project is easy to build, easy to use, and a great way to learn more about how phase-locked loops work.

Bicycle Gear Position Indicator
September 2009
Here’s a couple of simple circuits to tell you what gear your bicycle is in while you’re pedaling down the road. I usually check what gear I am in by looking down at the front and rear gears. I decided I needed a better way after I bought a good road bike with 30 (!) gear combinations (three gears in front and 10 in back).

Radio Locator Beacon For Flying Objects
May 2009
Exclusive Online Article: The locator beacon weighs about an ounce with its 12-volt A23 alkaline battery, and could be made lighter with the use of surface-mount parts. It’s also simple and inexpensive, so you can afford to build another one if necessary.

Model Train Switch Control via PC or PIC
August 2008
This is a project I wanted to do many years ago when I was spending a lot of time and money on my model railroad. I was disappointed by the big, clunky electrical controllers which operated the track switches, and I wanted to have something smaller and more elegant to do the job. A computer control system would have been ideal, but I never got around to designing one. Many years and several designs later, I have come up with two versions of the control system: one PC-based and one PIC-based...

Single Chip, Four Channel Datalogger
January 2008
Use this inexpensive datalogger to sample analog voltages, convert them to digital values, and store the data in non-volatile memory.

Digital R/C Airplane Camera
December 2004
I’ve always been interested in photography and, when I first saw an advertisement for a “key chain digital camera,” I had to get one. In fact, I got two, sincethey were inexpensive and so small that I figured I would lose one.

PIC-based Motorcycle Gear Indicator
July 2005
A while back, a friend of mine with a Suzuki Katana motorcycle sent me some plans he pulled off the Internet for circuits that would tell him what gear his motorcycle was in while he zipped down the highway. Since I’d helped him with some other electrical and electronic projects for his bike, he figured I could build one of these for him. I looked over the schematics he had found but wasn’t too impressed — most were for “strip gauges” which lit a different LED for each gear...

The Poor Man’s CNC Milling Machine
December 2005
Wouldn’t you love to have a fancy computer-controlled drilling and milling machine so you could make whatever part you needed? Wouldn’t you love even more to have the money one of those machines cost? Well, I don’t have either, but I do have an occasional need to fabricate a simple part or drill a custom circuit board.

A Simple Digital Tachometer
May 2006
I bought a used Nissan pickup truck a few years back that had absolutely no bells or whistles on it when it rolled off the assembly line. I wanted to make some “improvements” to the engine, and I wanted a tachometer to help assess the results (for better or worse). The add-on tachometers available in auto parts stores didn’t appeal to me, mostly because I knew I could make one myself if I put my mind to it. What I really wanted was a digital tachometer...

Two Axis Sun Tracker For Small Solar Panels
August 2007
This project is designed to maximize the output from your existing panel by turning it to keep it pointing at the sun, and (hopefully) making the purchase of another panel unnecessary...