I Have heard that I can put the Arduino into "sleep mode which makes it REALLY low power consumption.
Being who I am, I thought I would have a power saving mode and have a SMALL battery to keep it alive.
The RTC has an alarm output pin which I can use to "wake up" the arduino, and it would then turn on the main power.
Then the output of the power supply would go through a 7805 to re-charge the battery and power the arduino, and the rest of the circuit.
Well, as the battery would be on the output of the 7805, I would need to have a diode on the output to stop the battery back feeding the 7805.
Alas there is a problem there that the 5 v would become 3.8 volts (or what ever it is.)
Thinking back, to get around this problem I put a diode (same as the one after the output) between the GND pin of the 7805 and GND which would offset the drop.
..have a SMALL battery to keep it alive..
Alas there is a problem there that the 5 v would become 3.8 volts (or what ever it is.)
Thinking back, to get around this problem I put a diode (same as the one after the output) between the GND pin of the 7805 and GND which would offset the drop.
Not good. You will drop the voltage even more, to 5V - 2x Diode_drop.
The best way is to put the SMALL battery (what does it mean SMALL?) at the 7805 input (btw, there are better voltage regulators today) with help of 2 diodes.
That might work as the diode from "7805 gnd" to gnd will increase the 7805 output voltage by the diode drop.
Also mind the 7805 needs at least 2.5V higher input to operate properly (see the datasheet). Moreover you are upping the required input voltage by 0.7volt (the diode in 7805's gnd), that means your power source shall be something like 8.2V min to make 7805 happy. You may consider so called "low drop voltage regulators" which require input voltage 0.2V higher than its output.
Btw, I doubt you can connect the 4x1.5V battery directly as depicted in your schematics - consider at least a charging resistor as a minimum (to limit the battery charging current).
Also mind the voltage at "arduino power input" will be 6V unless the battery discharges itself to 5V.
6V may damage your "arduino" system and related circuitry when not using a proper voltage regulator at "arduino power" input (ie when using your own bare metal design)!
And mind the Arduino requires some minimal power voltage (when talking UNO for example) so 5-6V at its input may not make the Uno happy.
