1Selecting Voltage Detector and Threshold Voltage
This power management module is very versatile as it allows alterations to suit the need of the project.
First step is selecting which voltage monitor should be used. This is going to be dependent on the type of the source and the precision of the target voltage. If the target voltage accuracy is not critical but the high impedance is required then the Novotill circuit (the one explained in the project description) should be selected. The Novotill cirucit's threshold voltage depends on the color and the type of the LEDs used. For example a blue LED will result in a threshold voltage of around 2V while a white LED will produce a threshold voltage of 2.1V. An IR LED would produce a threshold of 0.6V while a RED LED would result in 1.23V.
Note however that the voltage threshold is going to be a function of the amount of visible and IR light reaching the diode as well as the temperture. Therefore for a stable voltage threshold voltage it is recommended to insulate the LEDs using tape.
If it is necessary to activate exactly on certain voltage level that should not vary with environmental conditions then an integrated voltage monitor can be used. Integrated voltage monitor devices have precisely trimmed voltage thresholds, but they come at a cost of higher power consumption. I would recommend using XC6135, or XC6136 from Torex Semiconductors or ISL880xx voltage detector circuits as they have one of the lowest current consumption I could find.
2Interfacing the power management cirucit
Once the power voltage detector has been selected the power management circuit is simply placed between the power source, the buffer capacitor and the target application power input.
The designer has two options for resetting the power management board and enabling the voltage monitoring. First is using the target MCU if there is one, where the MCU after completing the task will present a pulse to the RESET input of the power management. Second option is to place a comparator or opamp that will set the pin high once the supply voltage is reduced to a predetermined level where the application should be terminated.
These options for resetting the operation of the power management circuit allows for increased flexibility in the design if additional components are to be avoided both for price considerations and reduction in overall power consumption