post power-out eeprom write on PIC 18F452

[payrend]

18f452 pic write

need to write a few eeprom bytes after power loss. What may be my solution alternatives? battery, supercap, ... ? and how to switch back and forth? anybody has practical experience doing it?

regards

 

[predrage]

battery monitor using 18f452

You can use low voltage detection. Take a look at 189 page of 18F452 datasheet. Write few words more about your application. Do you need to save some values in eeprom before pic turns off or you device should continue to work on batteries power supply?

 

[haytham]

write pic eeprom at power fail

hi
use Back up battery that will be connected to PIC IC when power failure condition is detected. The swiching to the battery should be made electronically by using a simple diode. The MC should always monitor the supply voltage as digital input. If it founds zeror while it is powerd ON, then it is working with the battery as the ct supply. In this cas eit shoould save what ever needed and to turn OFF, it could disconnect the battery path by using transistor.

Kindly F.B. if you have any questions

Thanks

Added after 1 minutes:

I forget
Kindly, if this worked with you don't forget tp press the "helped me" button to increase my points

Thanks

 

[Alan69]

need to write a few eeprom bytes after power loss. What may be my solution alternatives? battery, supercap, ... ? and how to switch back and forth? anybody has practical experience doing it?

regards

Use a large cap on the output of your regulator. Then a voltage divider on the input side of your regulator, set so you have a high while power is coming in, and when it goes below what the regulator has to have on the input you should have a few writes before the output cap is gone. If not make it even larger..



Ah yes, haven't used this in a while. If you can, use a diode out of your regulator to the microcontroller supply. Most regulators will drain the cap some as they go down, the diode makes sure everything left in the cap goes to the uC..