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+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+ <title>ClunkPi: driving pulse clocks with a Raspberry Pi</title>
+ </head>
+ <body>
+ <h1>ClunkPi</h1>
+ <p>ClunkPi is an add-on board to interface a Raspberry Pi to a
+ pulse clock. It is designed to fit all models of Raspberry Pi,
+ from the Model A onwards. It can operate any clock that's
+ compatible with the British Post Office class A system,
+ including movements made by Gents, Synchronome, and English
+ Clock Systems. ClunkPi can be driven by the
+ <a href="/clunk/">Clunk</a>
+ software to provide an NTP synchronised pulse clock.</p>
+ <h2>Specifications</h2>
+ <p>ClunkPi fits the 26-pin I/O header on the original Raspberry
+ Pi. It should also work on the first 26 pins of the 40-bit
+ header used from the Model B+ onwards. The board is smaller
+ than either a HAT or a uHAT, so it should fit many cases.</p>
+ <p>ClunkPi is essentially a switchable current source. It
+ provides a current of 250 mA ±10% into a resistance of up
+ to 12 Ω. It is switched by GPIO line 17 from the Pi. It
+ is powered by the Pi's 5 V line, from which it needs
+ 250 mA.</p>
+ <p>In theory, it should be possible to run ClunkPi off a higher
+ voltage to drive multiple clocks, up to the 50 V limit of
+ the drive transistor.</p>
+ <h2>Design files</h2>
+ <p>I designed ClunkPi using
+ <a href="http://kicad-pcb.org/">KiCad</a>. The KiCad source
+ files, along with the Gerber files for PCB manufacture, are
+ available for download.</p>
+ <h2>Circuit description</h2>
+ <p>The circuit is a simple current source controlled by a shunt
+ voltage regulator. U1 and R2 control the base current in Q1 to
+ achieve 1.24 V across R1. D1 suppresses any voltage spike
+ caused by the inductance of the clock coil.</p>
+ <h2>Use</h2>
+ <p>Plug the board into a Raspberry Pi with the square solder pad
+ connected to pin 1 of the GPIO connector. Connect the clock
+ (either way around) to the pads labelled "J2".</p>
+ </body>
+</html>
~bjharris / clunkpi.git / commitdiff