A recent project required an inexpensive microprocessor that could be battery operated and indicate if the batteries were low. I chose Microchip's PIC16LF84A for the microprocessor because it was simple to program and could operate between 2.0 and 5.5 V dc.
However, the PIC16LF84A doesn't have analog or comparator inputs. To meet the design criteria for a battery monitor, I went with Microchip's inexpensive MCP100315 Microcontroller Supervisory Circuit. It costs $0.33 each in small quantities.
In the circuit, U1 is the PIC16LF84A microprocessor. R1 and D1 make up the low-battery indicator circuit. R2 is a 10-k Ω pullup resistor for the MCLR pin. X1 is a low-power 32.768-kHz oscillator. C1 and C2?68-pF capacitors?were needed so that the oscillator would operate properly.
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