Without resetting....Switching PIC over to Backup Battery

[financecatalyst]

Thanks for the answers. I checked the Nuts&Volts article, it actually uses 9V battery before 7805. I am using 3xAA, which puts 7805 out of picture.
I tried it with 2 diodes, what capacitor values & what types should I use to minimise current consumption as well and where should I place them to avoid resetting. I will check it on my breadboard before making my PCB and setting it there.
Currently it is still resetting, I tried it with few random capacitor values but no success.

Currently on my breadboard, one 4007 is attached to 5V line from 7805, and one from 4.5V battery set.

[El_AMPo]

Try only feeding the pic with a 1000uF capacitor when the power is cut and the switching from main to battery takes place.
How? leave the two diodes but after the regulator one for the battery, other for the regulated supply, add a 1000uf capacitor before the pic and raise the regulator voltage to keep the 5V

"...maybe could work" circuit diagram:



Is a good practice to make a power supply detection signal with a voltage divider or another diode after the regulator.

Also if i'm not wrong 16F877 will not work under 4.0 volts but similar ones work happy up to 2,0V like the LF version, saying that. change: or your pic, or your battery, or maybe a "low drop" diode will do the trick

[financecatalyst]

The problem was BOD, once switched off it worked with just 1000uF at the supply.