Systems, methods, and devices of the various embodiments provide a device capable of determining a blood property based at least in part on the measurement of the amount of light received by a receiver circuit with a limited current capacity by charging a capacitor with a low voltage power supply and intermittently discharging the capacitor through a light emitting diode. In some embodiments the device may be a pulse oximeter capable of taking blood oxygen readings. In some embodiments the device may be a heart rate monitor to determine a heart rate based on an amount of light passed through tissue. The various embodiments may enable pulse oximeters and/or heart rate monitors to be incorporated into small unobtrusive body patches, while enabling the pulse oximeters to operate from a power output equivalent to that of a small coin cell battery or printed cell battery.