Build a Conductivity Meter
Make a tool for measuring electrical conductivity using your phone, microcontroller, breadboard, and common electronic components.
Tools and Materials
- Download the Science Journal app
- Battery, 9V, and battery connector
- M3 screws, two
- Microcontroller base
- Screwdriver, Phillips head
- Jumper wires, five
- 0.1 μF capacitor
- 47 kOhm resistor
Facilitator NoteUsing a microcontroller as an electronic base, we are assembling a circuit that allows us to measure the conductivity of various materials and substances. This guide was written to support facilitators leading others through these steps to reach the later activities, Conductivity Explorer and Body Conductivity. The microcontroller connects via Bluetooth to most smartphones with the Science Journal app to provide us with readings in real time.
Once assembly is complete, you can begin exploring the world around you as you gain skill at using the Science Journal app. We encourage you to mix things up and experiment with your own ideas. But first, let’s build the meter.
This guide was written to support facilitators leading others with some previous experience with microcontrollers. If you would like to learn more about the parts of the circuit, we recommend beginning with the What’s Going On? section for some background.
Your microcontroller might look different than the one pictured here, and that’s okay. What’s important are the ports that you are connecting to, which are named in each step.
Set Up Your Microcontroller Base
Start at these steps to add an external sensor to your Science Journal setup. Connecting External Sensors
Using a microcontroller expands the app’s capabilities. A base keeps these extra parts together safely.
Mount your breadboard to the base using tape or the adhesive backing.
The breadboard allows us to implement and use a wide variety of sensors. Here, we are using the breadboard without a sensor to create an open circuit that we can easily close to make measurements.
Set Up Your Meter
- jumper wires
- 47 kOhm resistor
- 0.1 uF capacitor
First, identify these components for building your Meter.
You can use a wire cutter to cut your wire down to different lengths as you go through these steps to connect the microcontroller to the breadboard. This will help prevent tangles and make it easier to assemble and disassemble your setup. Note that the colors of the wires don’t affect their function, so you can either let the color be random or use color to establish a system that helps keep track of your connections.
Before you begin, note the red dots in the image. Breadboards have many ports, and the ports that share a row (the red dots) are internally connected to each other. As you assemble your circuit, keep aware of which ports you’re using to connect and which don’t.
1. Connect one jumper wire from the 3.3V port on your microcontroller to a port on your breadboard.
You can choose any of the ports in a row on your breadboard. We recommend the port closest to the microcontroller.
2. Connect another jumper wire from the AO port on your microcontroller to a port on the breadboard.
Choose a different row than your first wire. You can select rows that are closer together or farther apart depending on the length of your wires or the legs of your other components. One or two rows of separation helps with visibility without spreading your ports too far apart.
3. Connect another jumper wire from the GND port on your microcontroller to a port on the breadboard.
Your microcontroller might have multiple GND ports. You can choose any of them. The AO, 3.3V, and GND ports together provide the breadboard with its needed power and allow it to communicate with Science Journal via Bluetooth.
4. Connect your resistor’s legs to ports on the same row of the breadboard as both GND and A0.
You can plug the resistor with the colored bands in either direction.
5. Connect your capacitor’s legs to ports on the same row of the breadboard as 3.3V and A0.
The capacitor and resistor will both be on the same row as A0.
6. Connect another solid core wire to a port on the same row of the breadboard as 3.3V and your capacitor.
The other end of this wire will be left unconnected to your meter setup. Attaching a wire with an alligator clip turns this into one of your two leads.
7. Connect another jumper wire to a port on the same row of the breadboard as A0 and your capacitor.
The other end of this wire is also unconnected to the meter setup. You should now have two wires connected at one end to the same rows of the capacitor. Connecting a wire with an alligator clip turns this into the other lead for conductivity activities.
8. Plug your 9V battery into the connector, and then the plug of the battery connector into your microcontroller.
10. Congratulations, your meter is finished.Now you’re ready to begin some electrical experiments. Check out some activities here.
What’s Going On?
The meter you’ve built here is one that measures conductivity, the ease with which electric current flows through various substances.
In general, the flow of electricity through an object depends on two things: voltage and resistance. Voltage is the “push” that gets electric current to move, resistance is the “pull” that holds it back. Various materials offer different amounts of resistance to flow of electrical current, as you’ll see once you begin to explore with your meter.
The relationship between current, voltage, and resistance is called Ohm’s Law, after its discoverer, George Ohm. Mathematically, the equation for Ohm’s Law is:
Current = voltage/resistance
where current is measured in amperes, voltage in volts, and resistance in ohms.
Your meter is designed to measure the electric current that flows through an object as a percentage. A reading of 0% corresponds to no current flow and high electrical resistance (or an open circuit). A reading of 100% indicates plenty of current flow and little or no resistance. The scale is nonlinear, by the way, so don’t decide that doubling the percentage equates with either doubling the current flow or halving the resistance.
Breadboards are platforms for building circuits. They have multiple rows and columns of ports, and while some can look very different from others, they all function similarly. Generally, each of the ports in a row connect to one another, with five ports making up a single connected row. An inset or imprint down the middle separates rows that do not connect. You can connect rows to each other by inserting wire ends (or leads) from a single wire or component into them.
Resistors are used to control the flow of electric current. The resistors you use here are made of conducting carbon covered with insulating plastic paint, and are color coded to specify the exact amount of resistance they offer, in units of ohms.
A capacitor is a device for storing electrical charge, measured in units of farads or, more often, microfarads (μF). Designs vary, but in general, capacitors are constructed from two electrical conductors separated by an insulator. In circuits, capacitors are used to filter out electrical noise, smooth the flow of electric current, reduce sparking and power surges, and store energy.
In this circuit, the capacitor works in conjunction with the resistor to create a circuit that can supply a steady current in a wide variety of situations, where the resistance of the objects being measured might range from zero to infinity.
Optional: Build Your Meter Case
Make housing for your meter to increase mobility and protect your electronic components.
Time: 15 minutes
Tools and Materials
- Microcontroller setup from Build a Conductivity Meter
- One piece of chipboard
- Pen or marker
You can build housing of your own design for your microcontroller. Here are steps to build a simple case that will protect your microcontroller setup.
1. Trace both sides of a ruler across the center of the short side of your chipboard.
2. Trace the ruler going up the long side of your chipboard. Do this on each end.
These panels form the walls of the case.
3. Cut along the two lines at the center of the chipboard until you reach the line moving perpendicularly. Repeat on the other side.
You can cut these center flaps so that you don’t have to tape them down later.
4. Fold toward the center along every other line that you have not cut.
5. Fold the chipboard together along each bend until the flaps form walls. Tape the sides of the case so the flaps stay fastened.
You now have a case and can insert your meter.
6. Personalize your meter case.
Some examples of what you can do: Put holes where the battery indicator light is so you can see when your microcontroller is using power. Draw your circuit to better describe your components. Add a strap for easier carrying, or a smaller case to attach to store extra batteries or wires.