Jeff Epler's blog

5 January 2012, 23:12 UTC

Time to finish that languishing clock project!

A leap second has been announced at the end of June 2012.

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23 June 2011, 21:38 UTC

Side track: wwvb links

Chris asks what advantage GPS has over WWVB for my clock project. I don't have a good answer for that (except that having enough controls to select one of 4 mainland US timezones and whether to apply DST is undesirable). However, this did prompt me to do some googling about WWVB. I found some interesting links about generating WWVB signals at home.

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5 February 2010, 23:47 UTC

Soldering "helping hands" made with Loc-Line coolant hose

I ran across "Third Hand" and decided to make my own. The main feature of my version is the two-part circuit board clamp. The clamps were manufactured with Chris's help on Jr, his new cnc milling machine.

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10 November 2009, 16:00 UTC

Arduino Random Number Generator

Inspired by other designs I've seen online, most directly Rob Seward's design, I decided to build my own random number generator based Will Ware's "avalanche noise in a reverse-biased PN junction" (try this mirror of Will Ware's page). Also important is turbid which introduced me to the concept of hash saturation and the math behind it.

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29 August 2008, 0:49 UTC

Two-element capacitative touch sensor

As a distraction from my real project -- building a lightbulb alarm clock for the coming winter -- I've been playing with capacitative sensors. My first effort was a wire taped to a piece of metal foil, and that worked OK. The present iteration is a two-element touch sensor on a milled circuit board.

The sensors are each about 1" by .5" and are connected to the arduino by a 3-pin header. The components on the board are very simple -- two 1M resistors. With a combination of software running on the microcontroller and in the PC, the sensor is made into a virtual slider.

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6 May 2008, 3:02 UTC

Bah, it's garbage

Back in 2006, I got a PCI card from Futurlec with 3 8255 chips on it. I finally gave a serious effort at getting it to work, but as you'll read in the updated original article the board seems to simply be broken. Too bad!


3 June 2006, 15:25 UTC in projects

1MHz+ Quadrature Divider for attiny13

This untested code, along with an Eagle schematic and board layout, are for a quadrature divider that polls at over 1MHz. The R and S test points are used to program the device.

Like the 400kHz triple divider, this program uses a state table generated by "", and is GPL software.

For real-world use, external pull-ups should probably be added to the board's input side, according to the directions of the encoder manufacturer.

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2 June 2006, 18:02 UTC in projects

400kHz Triple quadrature divider for atmega8 and quadrature state table generator

summary I promised a single, 800kHz quadrature divider for the attiny13. Well, I haven't done that yet (I don't have any attiny13s to test on anyway), but I have something else instead.

As I mentioned earlier, Chris had already milled a servo control board for his lathe. Like the Etch Servo board, it controls two servo motors with a single L298 chip. Unlike the Etch Servo, it has 3 encoder inputs (X, Z, and spindle). His servo motors have 500-line encoders and have a no-load speed of about 4000 RPM, while the spindle will have a 1024-line encoder with index pulse, but rotate slower (much less than 2000RPM when threading). 133kHz is too fast to count in the PC, but divided by 8 or 16 it's very managable. is a Python program which generates a quadrature divider table. By changing 'N', 'M', 'x' and 'ux', it's possible to generate tables with different properties. After generating the table, a variety of tests are performed on it to verify that it is correct. Output can be a "C" array or a table of bytes for an assembler program.

qq2.S is a GNU assembler program that actually performs the quadrature division. According to my cycle counting, it polls at 470kHz when a 16MHz crystal is used, so it is expected to work reliably with a 133kHz quadrature signal. So far, though, it has been tested with a single motor spinning at hundreds of RPM. and qq2.S are released as free software under the terms of the GNU GPL.

Files currently attached to this page:



23 December 2005, 14:19 UTC

First Interesting Strobe Photo

17 December 2005, 15:53 UTC

SOIC-8 to DIP adapter board

15 October 2005, 19:11 UTC

4-axis half-stepping translator in AVR

5 June 2005, 2:30 UTC

a plug for Eagle3D

26 May 2005, 0:36 UTC

XY display update

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