Using the Clock
Setting the clock
If you press the upper button, the middle LED array begins to flash. This is the “setup” mode. The minutes can be set first. The bottom button steps backward and the middle button steps forward the values of the given LED array. You must press the button for each step, the count will not spin after a while. If you reach the correct value, press the upper button again to set the hours similarly. The clock will return to normal mode at the third press of the upper button. The seconds can not be set separately, it can be reset only when turning the clock on.
Functions of the clock
The top button, as previously described, is the “setup”.
Three levels of brightness can be adjusted by pressing the middle button in “normal” mode.
The bottom button turns off and on the display in three steps: first the display of seconds can be turned off, one single flashing LED will indicate seconds. Pressed again, the whole screen turns off, and only one LED will flash at the lowest brightness (battery saving mode). Pressed the third time, the display will return to normal status.
The external connector
In the upper left corner of the board you can find a six-pin connection point. There are two possible functions for it.
First, you can connect a battery to the two separate pads indicated with the inscription “Batteries”. The diode protects the circuit from the bad polarity. 3 or 4 serially connected AA batteries can ensure the functioning of the clock even for months, depending on the display mode. With 4 batteries the power supply from USB will have no effect, because the 4 batteries have a higher voltage together. 3 batteries can present a solution if power supply via USB stops.
The other function of “Ext_Conn” field is the ICSP programming of the controller. With appropriate equipment the microcontroller’s internal program can be overwritten. The microcontroller’s program code is read-only. If by accident someone overwrites it with a faulty code, only the manufacturer will be able to re-write it (by returning it to the user’s expense). If you insert a socket in the circuit board, you can write your own clock program, using a different microcontroller. Here are some ideas to expand clock functions: date, automatic daylight saving, alarm function: with “Ext_Conn” you can operate a radio or a buzzer.
Accuracy is ensured by the oscillation of the crystal. Because of manufacturing tolerances, temperature of environment and the two load capacities the oscillation frequency may differ from the nominal value. It will be higher at lower capacity and higher temperatures. Experience has shown an accuracy of ± 1-2 sec / week at room temperature with the parts included in the package. To correct it I recommend replacing the capacitors, but the maximum value should be approx. 2x47pF according to factory data. The two capacitors may have a different value, no need to change both.