Universal power supply for MCUs (Arduino, etc.)

Components used in the project

 

All components used in the project, except for the case, PCBs, wires, and male pin-header bumpers, are shown in the diagrams and labeled for easy comparison with the description below. Each component designation is shown in brackets (in red).

Case.

Since I do not have a 3D printer, I could not make a custom enclosure for this project. Instead, I bought a suitably sized translucent plastic food-storage box with a tightly locking lid from a home-goods store. The translucent case makes the LEDs visible from outside.

Price 2 USD.

Solar panel ( D1 ).

I had several solar panels of different sizes and power ratings. I chose a small 110x60mm, 5V, 1W panel. The rated maximum is almost impossible to achieve in practice: on a bright sunny spring day, I measured about 150mA. The panel also fit well on the enclosure lid.

The price of this solar panel is 2 USD.

Schottky diode ( D2 )

To prevent reverse current from flowing into the solar panel, a diode should be used. A Schottky diode is particularly suitable because, in this low-voltage circuit, it has a significantly lower forward-voltage drop, typically about 0.3-0.5V, than a conventional diode such as the 1N4007, where the drop is about 0.8-1V. I only had a high-current 1N5825 (40V, 5A), but a simpler 1N5817 (20V, 1A) would also be suitable for this project and has an even lower voltage drop, which is especially useful with a low-voltage solar panel.

Price of 1N5817: 4.5 USD for 50 pieces

Battery Charge Module (BMS) ( M1 ).

I used a TP4056 module with an onboard micro-USB connector. It can charge at up to 1A with a battery voltage of about 4.1-4.2V and includes protection against overcharging and over-discharging the connected Li-ion battery. The module also provides terminals for an alternative input power source, which in this project is the solar panel.

Because I did not plan to use more than one battery, higher charging power or voltage was unnecessary, although charging and voltage-converter modules for higher voltages are also available.

TP4056 module price: 2 USD for 5 pieces

5V step-up / boost module ( M2 ).

This module is required because the battery-charging module outputs the voltage of the connected battery, approximately 3.7-4.2V, while Arduino and other electronics in this project require a stable 5V supply.

I chose a compact and efficient Wavgat step-up module capable of supplying about 1-1.5A.

Price of the used boost module: 1.1 USD

Power connectors ( J1-J3, JP1, JP2 ).

The project uses three 2-pin PCB connectors.

• - (J1) for connecting batteries with wires or an 18650 battery installed in a battery holder.

• - (J2) for connecting the solar panel. I chose a connector instead of soldering it directly so the device can be disassembled easily.

• - (J3) for supplying the 5V output from the boost module to the breadboard.

To connect mobile-phone batteries, I needed the same type of connector used in mobile phones (JP1, JP2). For clarity, the single 4-pin connector is shown as two separate connectors in the diagram. I had three different batteries: one with 3 contacts and two with 4 contacts, and the positions of the positive and negative contacts were also different. I removed a 4-pin connector from an old donor phone, and it could be used with all of these batteries. Similar connectors can also be purchased on AliExpress. The different positions of the power and ground contacts are handled by the switches described below.

PCB connector price: 1 USD for 20pcs

18650 battery case price: 1 USD for 1 piece

Switches ( S1-S4 ).

The project uses 4 3-pin switches for PCB mounting.

Two of them are used to select the battery contacts from the mobile phone: one ( S1 ) for the first pair of contacts (GND), the other ( S2 ) for the second pair (VCC).

The third switch ( S3 ) is used to connect an alternative power supply to the charging module (solar panel)

The fourth switch (S4) turns the 5V boost module on and off. It saves energy by allowing the boost module to remain off when it is not needed, for example, while charging the battery or storing the device.

Switch price: 1 USD for 20 pieces

Voltmeter ( M3 ) and button ( S5 )

Voltmeters of this type are available in two-wire and three-wire versions. A two-wire voltmeter uses the same circuit both for its own power and for voltage measurement; this is the version shown in the diagram. A three-wire module has a separate power input and measurement connection, allowing it to measure voltages outside the module's own supply-voltage range.

The voltmeter has a three-digit display and is available in four colors.

The button (S5) was added to reduce the energy consumed by the voltmeter (M3), allowing it to be switched on only when needed.

Voltmeter price: 2 USD per piece

Button price: 2 USD for 30 pieces

Printed circuit board.

The project uses three PCBs: two 50x70mm boards as vertical side walls and one 70x90mm board as the "floor".

All elements of the device were soldered on "PCB walls".

It is convenient to connect the PCBs to each other using 0.5mm solid-core wire.

5x7 PCB price: 2.5USD for 10pcs

7x9 PCB price: 1.6USD for 5pcs

Breadboard

A half-size breadboard provides space for additional electronic components such as an Arduino board and various sensors. Power and ground are connected to the breadboard rails through wires attached to connector J3.

Half-size breadboard price: 1.5 USD per piece

Bumper connectors

I installed four double male pin headers on one of the side PCBs as bumpers to reduce movement of the device inside the enclosure. This is completely optional.

Bumper connector price: 2 USD for 30 pieces of 40-pin headers

 

Total component cost

The total cost of the project components, excluding tools and consumables such as flux, solder, and wires, was 13 USD. Excluding the breadboard, the total was 11.5 USD.

You can find all the components mentioned above, together with their links, in this Google document​​