In this sketch we want to give you a better knowledge on what is going on in a device like this. There is a first phase when you see practically nothing. In fact, the receiver needs some time to adjust itself to the signal level. Then you see pulses traveling one after the other, waiting for the begin of the transmission of a new datagram.
For some 30 seconds you just have to wait. A counter will show the elapsed time (unit is 100ms).
At some time you will see pulses travelling from right to left. There will be short pulses (100ms, the width will be 1 digit on the display) representing a logical "0" and long pulses (200 ms, the width will be 2 digits on the display) representing a logical "1".
At one point, there will be a long pause between pulses. If data were collected for 59 seconds and no error ocurred, the correct time is received and will be displayed. As we have only 4 digits, time and date are shown alternately (there is no space to show the year).
There are several methods of error detection: a minute start bit, a data start bit, three parity bits and some plausibility checks. If any of these errors occured, an error bit will be set and the error code will be shown instead.
Some causes for errors are:
The complete source
The "font" for the LED display (including special characters to display the waveform of the pulses)