This simple D.I.Y module is all about controlling two battery sources in series combination.Thereby it provides the functionality to manually switch between series or individual battery configuration output.

Step 1: Gather the Components and Tools.

For making the module you will require some components.You will mostly find them in the nearby electronic hardware shop(s).

The list of item(s) are as follows:

1.3x 2pin Screw Terminals.
2.A perforated circuit board.Cut them in 2cm X 2cm size approximately.
3.An SPDT or DPDT PCB mount switch.
4.Any two battery sources under 15V each.

Tools Required:-

1.Soldering Iron
2.Soldering Flux
3.Soldering Lead
4.A multimeter
5.Any load source(eg-LED,Motor etc.)
6.A strong adhesive.
7.A rubber adhesive.

Step 2: Analyse the Circuit Diagram and Place the Components Accordingly.

The circuit diagram is quite simple.The primary battery remains in contact to the circuit everytime.Only the second battery source gets switched.

At initial condition of the switch, the output only comes from the primary battery, but the moment when switch is moved to other position, the negative terminal of the primary battery shifts it's contact to the positive terminal of the second battery thereby giving a series output of voltages from the individual battery sources.

1.Now start placing the components in such a way that you need not require longer soldering traces and requires the least amount of overlapping junctions.
2.Place the screw terminals first.If it doesn't go smoothly into the perforated board, slightly enlarge the holes by the help of a small tip screw driver and then place the switch.
3.Once you are sure about the layout,glue them using a strong adhesive as the screw terminals may get displaced from its original position over long usage.
4.After that using two markers of different colors, mark the terminals of battery sources 1, 2 and at the output terminal.

Step 3: Soldering and Continuity Testing.

Now start soldering the terminals of the components by looking at the circuit diagram.In case if you come across any overlapping junctions, use small pieces of insulated wires and solder them.
For making sure that there's no short circuit(s) and no broken channel(s) have a continuity check.

Step 4: Testing of the Module With Two Similar and Dissimilar Battery Sources.

Once you have finished soldering, test the module by connecting the output terminals to the multimeter and connect the battery sources at its respective input blocks.
Check for the voltage displayed on the multimeter and check whether you get an average sum of two voltages of the individual battery sources.

Step 5: Gluing the Base of the Circuit Board With Rubber Adhesive.

Once all testing is done, glue the base of the circuit board with a rubber adhesive as it somewhat provides a better insulation to the base.

Step 6: Applications and Conclusion.

APPLICATIONS:-
1.The main application is to switch between a series output voltage or an individual output voltage from two different battery sources.
2. Controlling voltage also controls energy this means it can be used to create:
a) 2-SPEED motor.
b) 2-Level Brightness control Light.
c) Small Purpose Dual Voltage Power Supply.
3.When connected to a single battery source at primary terminal, this module can be used as a ON/OFF switch to control the battery output.

CONCLUSION:-
This small portable module may come handy for small applications and electronic projects.