A functional update for the IV-11 DCF melody watch is available from gr-projects. It is a radio temperature transmitter. The special thing about it is, that the transmitter operating in the ISM band 433 MHz is equipped with a photovoltaic cell (solar cell). Depending on the version, a small rechargeable battery or a CR2032 button cell can be installed in the transmitter. The battery is thus supported by the solar cell in the sunlight or in the battery version it is charged during the day and then keeps the transmitter in operation over the dark time.
The assembly is easy. The kit consists of a transmitter and a receiver. The boards of transmitter and receiver are equipped with few components quickly. Here, however, some attention is required and you should read the documentation carefully, because due to the lower number of kits, the boards are manufactured without component imprint and solderstop.
The radio modules themselves are completely pre-assembled (SMD) and only need to be soldered into the corresponding circuit boards. Optionally, a trim potentiometer can be connected in parallel to the temperature sensor (NTC) for adjustment purposes. The transmitter, like the receiver, is installed in a small PVC housing. Here, except for a 3mm drill hole and possibly some silicone for the sealing of the solar cell (for operation outside the window sill) no further tools are needed.
To connect the receiver to the clock, make a few minor changes to the clock’s mainboard. First, the microcontroller is replaced – logically – because there is indeed a new program that then displays the temperature in the date line. A resistor is removed, one is added and a jumper can be swapped. The connection between the clock’s motherboard and the radio receiver is made with a piece of cable. Three lines are required (GND, + 5V and the data signal from the receiver controller to the clock controller). That’s it then already. The clock can go into operation. After a few seconds, the received temperature is displayed in the tube.
A video how to solder the circuit is available here: