EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: don.r on September 23, 2019, 04:06:48 am
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I recently acquired an HD radio since stations have started appearing in my area. Its a vintage 2007 Sony XDR-S3HD and is a spectacular FM receiver. One of its shortcomings is a lack of battery backup for the presets, configs, etc. so that when the power goes down or I unplug it, I lose everything. I was thinking of re-purposing an 18650 cell to act as a backup. The micro uses a 3.3V line fed by IC902. My plan was to use a diode from the 4.9V rail that feeds IC902 and add a 100ohm current limiting resistor. This should feed the cell a maximum of 4.2V. From there I would add another diode and another 100ohm resistor (just in case!) giving 3.5V and tap into the 3.3V line after D907 on the 3.3V regulator's output. The CPU has a 2.7V to 5.5V input range. Thoughts?