FunkUsb: Radio controlled clock receiver with USB

A DCF77 time signal receiver with USB connection.

FunkUsb emulating a serial interface (COM port)

Impulsion

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

However, one line will not work at all, and another one not within “Funkuhr.exe”. DCD, DSR, RI and RxD will work. 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

                           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

 

Programming

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.

Driver installation for the COM port may be complicated!!   Choose your operating system! Windows 98, Me Windows 2000, XP Windows XP 64 bit Windows Vista, 7, 8, 8.1 — 32 bit Windows Vista, 7 — 64 bit Windows 8, 8.1 — 64 bit Windows 10, 11 — 32 or 64 bit Linux MacOS

Usage (Windows)

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 dimmed. On aerial signal (carrier attenuation) the LED lights up. For enabling this effect, the running receiver software must activate either TxD or DTR. In USB standby mode, the LED is off.

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 11 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

Solution

• No driver issues; every USB-capable system supports joysticks without a need for extra driver, possibly on Windows 95c too
• Function check without third-party tools using Control Panel / Game Controller. See animated screenshot.

  Note: The Windows 98 Control Panel application refuses to work properly. For the same reason as joySetCapture() expects two levers. FunkUsb.exe uses joyGetPosEx() instead.

• Measurement of time is done in real-time capable microcontroller, decoding data doesn't rely on low system load.
• The Microcontroller's size can be smaller (ATtiny25 statt ATtiny45) and thus be cheaper

• Loss of compatibility with software expecting a COM port. Then use firmware above instead.

My „Funkuhr.exe“ application is extended to know this HID Interface.

Moreover: The firmware source code allows easily configurable port pins and is suited for both gcc3 and gcc4.

Journal Review

Linux Usage

Nevertheless, my dcf77-js.c can set the system clock. This source code doesn't depend on uncommon libraries, is easily compilable, and useful for setting the system clock of a Raspberry Pi.

The program uses /dev/input/js0 as default device. The one-and-only command-line parameter selects another joystick.

The program runs in one of two modes:

• As unprivileged user, DCF77 data will be decoded and displayed endlessly with colored characters. Nothing else. See screenshot.
• Started as root, DCF77 data reception runs until two adjanced telegrams are received error-free and with 1 minute difference. Then it attepts to set the system clock, and terminates.

The archive contains an x86-64 binary image file.

FunkUsb as Prefetching Receiver

See German version of this page for further details.