Introduction
Aims
In this part of the activity we will:
- Add a voltage divider and understand how it works
- Record voltage using a microcontroller
- Visualise the voltage on a computer screen as a chart
Learning outcomes
| Learning outcome | |
|---|---|
| Electronics | Understand how to use a breadboard |
| Electronics | Understand, create and use a voltage divder |
| Mechatronics | Read an analogue signal using a microcontroller |
Preperation
Equipment required
| Equipment item | Quantity |
|---|---|
| Custom wind turbine kit (you just assembled it!) | 1 |
Tools required
| Tool | Quantity |
|---|---|
| Multimeter | 1 |
Why use a voltage divider?
Feeding a voltage into a microcontroller
The microbit can measure an analogue voltage input of up to 3.3 volts.
Our voltage is higher than 3.3 volts so we will need to reduce it! If we don’t we will damage the microbit.
What is a voltage divider
A voltage divider helps us to reduce (step down) a voltage to a lower level.
It’s a type of electronic circuit that looks like this.
We can use an easy formula or calculator to find the values of resistors that we should use in the voltage divider.
Try that now. If the maximum voltage from the wind turbine is 5 volts. Use the calculator to find which resistor values we will need to use in the voltage divider. One of the resistors values must be 330 Ohms.
Let’s create the voltage divider
First make sure you have connected to the positive and negative voltage of the motor terminals
Position your crocodile clips onto your motor terminals.
Connect the other end into your wago connectors
Understanding the breadboard
The breadboard lets us easily create electronic circuits.
We can stick wires into the breadboard
All of the columns of holes of the breadboard are connected together with metal strips.
This means any wires we place in the same columnn are connected together.
Creating our voltage divider in the breadboard
Create the voltage divider. The image below shows you how to do that.
You will have to cut some wires (jumpers) to the right length.
You will need to use the wago electrical connectors and the crocodile clips.
Check you voltage divider with a multimeter
Use the multimeter to measure your voltage divider.
Turn the wind turbine shaft with you fingers.
You should find that the reading is postiive and does not exceed 2 volts. If this is not true please seek help from a mentor.
⚠️ Do not go past this step until you have shared your setup with a mentor. It’s possible to damage the microbit if there’s too much voltage.
Readimg the analogue input with the microbit
Connect the output from the voltage divider to the microbit
Following the circuit diagram shown in the image below
You will need to use the wago electrical connectors and the crocodile clips.
Create your program
Go to micro:bit make code and start a new program
Enter this code. You will need to use:
- Pins
- Variables
- Serial
Download it to your microbit
You will need to:
- Insert your usb lead
- Connect your device (as shown in the image below)
Run the program
Go to show data - device
You should see:
- A heart shown on the microbit display
- When you rotate the shaft of the wind turbine clockwise, then the microbit reads the analogue input
Convert it to a voltage
Currently the microbit reads a voltage from 0 to 3.3V and maps it to a number from 0-1023.
To convert this back to a voltage it’s easy we just need to use this simple formula
We need to multiply again by 2 because of the voltage divider (which reduces the voltage by half)
Adjust the program
Let’s adjust the program to reflect this
We should see the serial values now appear in volts
