Hi...
I managed to get my latest clock running with a 7447 as per my previous post without a ULN2003, but now I have another question.
I'd like for this clock to have a battery backup. I figured it'd be a simple task of adding a cr2032 along with a couple of steering diodes and a resistor to make sure that the battery voltage was a little lower than the supply voltage. That's not working, though.
I am attaching a copy of the power supply circuit I am using. The 12v supply goes to the digit LEDs. The 5v supply goes to the SN7447. The only thing that the 3.3v supply goes to is the MSP430's VCC pin1 and the reset pin16 through a 47k resistor.
With the 12vdc adapter plugged in, there is about 2.6-2.7vdc on the 3.3v line. With the adapter unplugged, there is about 2.0-2.1vdc on the 3.3v line from the cr2032 battery. My code is written so that the main loop continuously scans the display with the watchdog timer taking care of updating the time, which is stored in the variables hh, mm and ss.
I would think that as soon as the mains supply is removed, the battery should power the processor and that the MSP should be able to continue updating the time, and scanning the display, even though the display will not light since the LED and 7447 power supplies are removed. That is not what is happening, though. I can set the time, unplug the adapter and as soon as I plug it back in the display is flashing 12:00 again just like it is being powered on for the first time.
Any ideas as to why this is not working? I'm open to any suggestions/criticism/feedback. Thanks.
