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FunkUsb: Radio controlled clock receiver with USB

A DCF77 time signal receiver with USB connection.

FunkUsb emulating a serial interface (COM port)

This is done using CDC USB class and works with Windows 2000 to 7, 32 or 64 bit, and with Linux. Should also work with Windows 98, Me, and MacOS.

Impulsion

Most widely spread DCF77 radio-controlled clock receiver are connected via the serial port. Today's laptops require some USB to serial solutions for connecting such equipment.

Occasionally, radio-controlled alarm clocks get out of work, but the DCF77 receiving module is still intact. But why making a voltage shifter for connecting a serial port when there is a nice USB solution there? Here, a small 8-pin ATtiny45 is sufficient, filled with smart firmware called V-USB and AVR-CDC. With this firmware combination, the DCF77 receiver creates a serial port and is fully compatible to old-style true-serial-port ones. No software adaption is necessary.

Function

The signal received should stimulate all five input “pins” of the emulated serial port. Therefore, software settings are no more critical.

However, one line will not work at all, and another one not within “Funkuhr.exe”. DCD, DSR and RI will work. RxD and CTS won't work. The receiver has to be activated using any of the three output “pins” of the emulated serial port. However, one of these lines will not work at all. TxD and DTR will work. RTS doesn't work.

The software installation procedure below is for Windows (2k, 2k3, XP, Vista, 7). Linux and Mac users should know what to do.

Circuitry

The microcontroller and the DCF77 receiver will be fed by regulated 3.3 V. The internal 16.5 MHz oscillator is used for clocking, synchronized by SOF pulses onto the DATA– wire of USB by the host computer.

                           TPS71533DCKR
                             5╔═════╗4
3P3 ───┬────────────────────┬─╢O G I╟───┬── 5P (1)
      +│ 4,7µF              │ ╚╤═╤═╤╝   │
      ═╧═ ┌─────────────────┼────┘2     │
      ═╤═ │ 1╔═════╗╔═════╗8│ ╔═════╗   ▼ LED yellow
       ├──┘  ╢     ╚╝     ╟─┴─╢1,5kΩ╟─┐ ┬
       │    2║            ║7  ╠═════╣ │ │
SIG ───┼─────╢            ╟───╢ 47Ω ╟─┴─┼── D- (2)
       │    3║            ║6  ╠═════╣   │
ENA ───┼─────╢            ╟───╢ 47Ω ╟───┼── D+ (3)
       │    4║            ║5  ╠═════╣   │
       ├─────╢  ATtiny45  ╟───╢470Ω ╟───┘
       │     ╚════════════╝   ╚═════╝
GND ───┴─────────────────────────────────── G╧ (4)
┌──────────┐
│  DCF77   │                             ┌───────┐
│ receiver │                             │  USB  │
│  module  │                             └───────┘
└──────────┘

Construction

The assembly

 
The soldered TPS71533 (voltage regulator)

Programming

The chip is programmed using an external programmer.

The Firmware is freeware (FunkUsb.c: Public Domain; V-USB part: GNU LGPL). The firmware contains a new approach for synchronization of internal RC oscillator, and lots of changes at AVR-CDC for support of virtual modem state lines.

Installation

Note that DOS software will not run with FunkUsb. Windows does not virtualize port addresses.

After installing the driver, the device will not automatically run nor a clock will automatically set. This is done with the next program, for example.

Usage (Windows)

For receiving the time and setting the clock, I have written the program “Funkuhr.exe” (has English and German GUI, but only German help file).

You can use any receiver software of your choice, but it must be Windows (not DOS) software that accesses a COM (not LPT) port.

Normally, the LED lights dark. On aerial signal (carrier attenuation) the LED lights up bright. For enabling this effect, the running receiver software must activate either TxD or DTR. The LED is completely off in USB standby mode.

FunkUsb emulating a Joystick

• The firmware fits into 2 KByte flash of cheaper ATtiny25
• No driver installation hassle at all, runs perfectly from Windows 98 upto Windows 8 64 bit
• Function can be checked without any additional Windows software at all, see screenshot on right side, taken from built-in Control Panel application.
• Requires clock-setting software that accepts a joystick button as input device

See German version of this page for further details.

FunkUsb as Prefetching Receiver

See German version of this page for further details.