Jeff Epler's blog

Time to finish that languishing clock project!

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

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.

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

(M)(L)

Two-part clamp grips circuit board

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.

Arduino Random Number Generator

Random Number Generator Schematic

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)

Two-element capacitative touch sensor

(M)(L)

Touching the sensor

(M)(L)

The finger position readout

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.

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!

1MHz+ Quadrature Divider for attiny13

Quadrature divider board. Actual size: .7x.4 inches (about 18x10mm)

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 "mkstate.py", 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.

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

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. Update, 2007/01/04: Want true high-resolution PWM and multi-MHz quadrature counting with emc2, for under $100? Try this!