Introduction: Learn How to Make a Portable Battery Powered Monitor That Can Also Power a Raspberry Pi
Have to ever wanted to code python, or to have a display output for your Raspberry Pi Robot, on the Go, or needed a portable secondary display for your laptop or camera?
In this project, we will be constructing a portable battery-powered monitor and power supply that can also power a raspberry pi, or charge your phone. We will use a lithium-ion cell battery and use both buck and boost DC to DC converters in order to build our project.
Be wary and remember safety reminders are in bold.
You will need:
-A Raspberry pi (any board will work, just note the volage requirement and current draw for later reference) and necessary adapters and power cords :
-An LCD 12 VOLT rated monitor (I used a 7-inch screen);
-A DC TO DC buck converter with USB output:
-A DC TO DC Boost Converter:
-Single-core small and medium electronics Wire of which can handle at least a maximum of 10 amps
-USB Power cord
-A Suitable Barrel pin for display:
-(Optional) A 3d Printer to print mounting parts and battery case if needed
-A battery holder:
-A suitable switch
-18650 battery cells in even quantities ( Excersize extreme caution when buying lithium-ion cells from vendors who you are unfamiliar with buying from )
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Step 1: Understanding the Basics
Here is a quick run-through on the theory and principles behind the project, as it is important to understand the basic electronic principles behind this project.
Firstly let's assess the core components we chose. We chose a 12-volt monitor for this project, and a raspberry pi operates at a voltage of 5 volts and requiring up to 3 amps to maintain power depending on which raspberry pi board is used.
Next, let's discuss our power source. Lithium-ion cells (on average having a capacity of 3.5 V), are being used to power this project, in a 2S configuration (The cells are ordered in cell groups of which contain two cells wired in series, which each cell group being wired in parallel to each other). As such the battery can output an average voltage of 7 volts and its current output and capacity being determined by the number of cell groups being used.
Now, let us go over our power regulation system. Due to the battery's output not being initially satisfactory to power the project efficiently on its own, DC to DC Voltage converters are required to convert the output voltage of our battery to that of the required voltage of each device (leading to an alteration of the batteries maximum output load current also), either by raising or lowering the voltage(hence lowering and raising the current respectively). As the raspberry pi requires a larger load current than out display, the Voltage will have to be reduced to meet the raspberry pi's required voltage and load current minimum
Hence leading to our 2S battery configuration is ideal for the task at hand (due to there output being around 7V) as it is close enough to the nominal voltage of the raspberry pi to also provide ample load current and close enough to the nominal voltage of the screen such that when the voltage is increased, there will be enough current to still operate the screen.
The DC to DC Voltage converters being used in the project are:1) a boost converter, this will increase our 7-volt input, to a steady 12-volt output for use by our monitor and 2) a buck converter, this will decrease our 7-volt input to a steady 5-volt output with an ample supply of current for the most intense of operation.
This project can also be done in various ways, like doing the project such that only the display will be battery-powered, in which case all you will have to do is follow the guide, and disregard the steps for the set up of the raspberry pi.
Also, this project can be used to power a phone or any other USB powered device instead of a raspberry pi board, if you disregard all the parts of each step dealing with the monitor or any variations of such, hence knowing the basics taught here is instrumental to any further improvements or modifications.
Step 2: Starting the Build and Printing the Parts
Now that you understand the basic electronic operations of this project we can commence our build.
This project is mostly electronic, but if you want everything in a neat package or don't have certain parts. You can 3d print them first so you can focus on the electronics later down.
If you used the recommended monitor you can use this file for your harness (included in step).
If you need a battery holder you can check out: https://www.thingiverse.com/thing:1823552. You can follow the creator's instructions, or you can bore your own holes and use m2 to m4 screws, bolts and washers to clamp your cells and wiring. Remember to double-check your connections and insulate all open connections and conducting screws before continuing onwards.
Step 3: Wiring Your Battery
Before you start, ensure that you have all the required components and remember to check if your 18650 Cells are of similar voltage and capacity
First, group your 18650 lithium-ion batteries in pairs and connect each pair in series forming a cell group.
Next, take each cell group and wire each of them in parallel to each other, and remember to wire a switch to one of the parallel junctions (preferably the first or last or at the output of the battery).
This is seen in the wiring diagram above.
Remember again to double-check your connections and insulate all open connections and conducting screws before continuing onwards.
Step 4: Connecting Your Voltage Regulators
Next, we will connect our DC TO DC voltage Regulators to our battery.
First, ensure that the switch placed on the battery as shown before is off before wiring to prevent component damage during calibration.
Next wire the positive terminals of the battery to the positive both the buck and boost converters in parallel.
Next wire the negative terminal of the battery to both the buck and boost converters in parallel.
This is shown above.
Next, turn on the switch and use a screwdriver to adjust the outputs of the boost and buck converters by turning the boards' potentiometers
The boost converter will power the 12 VOLT Display and the output must be calibrated to have a 12-volt output
The Buck converter will power the Raspberry Pi. As mentioned earlier each board has a different current requirement. Set the buck converter to 5 Volts and set it to USB mode (can be done via the of included documentation in packaging for the component) and set Current Regulations to 1amp and calibrate based on board once it is connected later on.
Step 5: Connect Your Screen and Raspberry Pi
After calibration of voltage regulators, we can connect our devices
First, we can connect our barrel pin to the boost converter output in proper polarisation and you can then connect it to the screen.
Next, connect your USB to the Raspberry Pi and then hook up your HDMI from your Raspberry Pi to Screen.
Now use a screwdriver and adjust the buck converter's current cap to a value at which the raspberry pi board turns on and boots (can vary from 1 to 4 amps depending on the board used).
A cell phone can be used here if charging a cell phone is to be done, instead of powering a raspberry pi, Just ensure that the amperage at which you limit potentiometer is set to that of the specifications of your device.
Step 6: Wrapping Up
Now the electronics is done and now you can Tie up all your cables and it is time to wire up the LCD harness
You can fit the boost converter and battery pack to suit your means either by hot glue or bolts and if you are using the included printed harness you will:
1)Secure all the components either via double-sided tape, drilling holes in the 3d printed model to suit your components and securing with screws or with twist ties , to the 3d model
2) Remove the display stand form the bottom of the monitor to expose slot in which the model will be inserted
3) Slide the tab of the printed mount into the slot on the back of the monitor from the bottom, until the mount is secure.
4) Screw back in the stand to lock the mount in place and to secure components.
Step 7: Conclusion
Now you have a battery-powered Raspberry Pi and Display, to go forward you can add a wireless keyboard and then a camera. Also via this project, you have deepened your understanding of electronics and how basic items that you use in your everyday life, such as batteries and smartphones work and are powered.
Step 8: Future Steps
This project can be improved in the future by the addition of a 3d printed casing in which all the existing components can be stored and protected from the external environment.
Also, an integrated battery charging circuit can be added to charge the device without removing the batteries and more cells can be added such to improve battery life.
You can adapt this project into a Battery bank or Just a battery-powered Display and In the future, you can also increase your battery capacity and maximum load current output by connecting more 2S 18650 cell groups in a similar configuration in parallel with the current cells.
This project can be further expanded into a matrix of displays and raspberry pi's via the expansion of the cell groups of the battery and the repeating of each step within this project. This project can hence be used as a backbone on which you can expand your battery-powered matrix of Displays and Raspberry pi's
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