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DCF77 decoder

A project log for easy-alarm-clock

Improvements for the ubiquitous alarm clock

Christoph TackChristoph Tack 04/13/2019 at 12:500 Comments

Assembled unit (lid removed to show internal construction)

Design

Schematic design and PCB layout can be found on EasyEDA.

Housing

The DCF antenna doesn't work well when it's in proximity to EM-noise sources.  Possible noise source are the rest of the electronics of the clock or a laptop.  The solution is to put the DCF-antenna and the decoder in a separate housing.  It might not be necessary to use the separate housing once the clock is properly designed instead of using the breadboard and flying wires.

Steps to follow:

Main components

Connector

It should be easy for the customer to find a suitable cable assembly to connect the box.  The connector should also be small and low profile.

The initial idea was to mount a TRRS audio headset socket directly on the PCB,  Doing this would make it hard to correctly drill the needed hole in the front panel.  Moreover, such a connector, which needs to be placed against the wall of the housing would require a longer PCB than stated in the datasheet of the box.

Two JST XH connectors will be used instead.  One connects to a panel mount TRRS audio headset socket.  The other connects to a panel mount LED.

Cable assembly

Many audio cables are constructed as two pairs of two wires.  So the left and right channel each have their ground wire in close proximity.  The ground wire is connected to the sleeve.  To take advantage of that cable configuration, the GND signal is here also connected to the sleeve.

JST XH
SignalAudio jack
23V3Tip
1OUTRing
3GNDSleeve

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