My requirements are: I need a UPS system which supplies power to a 9 volt modem. UPS should Charge 12v battery (SLA , charging curent 800ma), and it should have overcharge/discharge protection system [optional: it should show the battery capacity with four leds(25% interval)]. I want to achieve this without using ADC. I can make 230V AC to 12v DC converter with step down transformer. Switching from mains to battery can also be achieved with two diodes. But i want to make overcharge/discharge with led indicator which i cant figure out without ADC. Is there any way to achieve this without microcontroller and ADC. Any suggestion would be appreciated. Thanks in advance.
I am thinking about something like this. I have designed this circuit on my own. But i have no idea how to link these two switches to charge level indicator.