As mentioned earlier, electric current in a circuit is the flow of electrons through that circuit. The flow of electrons in a circuit can do things like make its light element glow, make its motor turn, and so on. Current through a circuit is the result of an electrical pressure called Voltage, which typically has to be connected to a circuit to make the current flow.
In this activity, you will set up supply voltages on the bus strips so that sockets with supply voltages are adjacent to every terminal strip row. This will make it convenient to connect supply voltage to any terminal strip row that might need it. You will make a lot of those kinds of voltage connections to your circuits in upcoming activities.
You will also use the micro:bit running a voltmeter script to check the electrical connections and make sure each one has the correct voltage.
BLANK? Disconnect power! If the display is blank, or only displays the symbol briefly before going blank, disconnect power immediately and check your wiring for errors.
Like the script from First Electrical Connections with a Breadboard, this script is also pre-written as a hex file with the multimeter module added.
Now let’s test the supply rails, first with the Python Editor and then with CYBERscope. In these tests, you will verify that the rails now have 3.3 V.
The wires you added to the breadboard it easy to connect circuits you build on the terminal stips to supply voltages on the bus strips.
The two levels of supply voltage in your prototyping system are 3 V and 0 V.
You can connect a circuit to 3 V by plugging a wire or lead into one of the center and right bus strips’ plus (+) sockets. Those are the ones next to the red lines, and also shaded red in the animation.
The other supply voltage level on the breadboard is 0 V, which is also called ‘ground’ and abbreviated GND. The 0 V level is available from all three bus strips’ minus (-) sockets. Those are the ones next to the blue lines, and also shaded blue in the animation below.
(View full size: bb-voltage-zones.mp4 [6])
Current: Electric current is the flow of electrons through a circuit. Every time a light turns on in your micro:bit module’s display, it’s because current is flowing through it.
Amp: Current is measured in amps, short for amperes, and abbreviated A.
Voltage: The electrical pressure that causes current to flow through your circuit. When the micro:bit’s built-in microcontroller makes a light turn on, it does so by applying voltage to the circuit. That’s the electrical pressure that causes current to flow and the light to turn on.
Volt: Voltage is measured in volts, abbreviated V. Although we’ve been calling it “electrical pressure”, the volt is more correctly a measurement of electric potential. The volt is named after 18th century Italian physicist Alessandro Volta.
Millivolts and milliamps: Abbreviated mV and mA, the millivolt is 1/1000 of a volt, and the milliamp is 1/1000 of an amp. Example: If you measured 3.28 V across the 3V and GND, that could also be expressed as 3280 mA.
Supply rails: When the (+) and (-) columns carry supply voltage, they are sometimes referred to as the positive and negative supply rails.
When the system is connected to a USB port, 3 V is actually very close to 3.3 V, typically 3.28 V.
If there’s no USB power and the system is connected to a battery supply, 3 V is determined by the battery voltage. Depending on how new the batteries are, it could range anywhere from 2.6 to 3.2 V.
A multimeter is a device that can test for continuity and measure voltage, current, and several other properties that will be introduced as you progress through these lessons. A multimeter’s voltage measurement setting makes it function as a voltmeter. When it is set to measure current, it functions as an ammeter. It’s easier to remember that name if you think of it as an amp meter, with the ‘p’ and space removed. You will be using your micro:bit and a web app to take various multimeter measurements, but a device like the one Digital Multimeter BBT858L is an even better tool for taking those measurements.
Voltage is a measurement of the difference in electric potential between two points. That’s why you get a measurement of about 3.3 V when you connect the P2 alligator clip’s red probe wire to 3V and the P0 alligator clip’s black wire to GND. The difference in electric potential between 3.3 V and 0 V is:
3.3 V - 0 V = 3.3 V.
Let’s try something different.
Repeat the arithmetic example for the 3.3 V result for the three measurements you just took.
Solutions:
The CYBERscope is a web page app that can work together with your micro:bit to take various multimeter measurements. It can also take other types of measurements, like oscilloscope and logic analyzers, but those will be introduced later. This web app works with Chrome browsers that are Version 89 or newer. The cyberscope.parallax.com page will tell you if your Chrome browser version is compatible.
Up-to-date Chrome Browser
Older version Chrome browser -needs updating!
Instructions from here downward are only for browsers that displayed the message with the red banner. If you didn't see the red banner, just continue to the next page.
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Now let's try out the CYBERscope page’s voltmeter display.
Don’t forget to save your work.
Links
[1] https://learn.parallax.com/tutorials/language/python/breadboard-setup-and-testing-microbit/connect-microbit-breadboard/first
[2] https://learn.parallax.com/sites/default/files/content/Python/breadboard/mp4/mangnify-power-connections.mp4
[3] https://learn.parallax.com/sites/default/files/content/Python/breadboard/hex/measure_volts.hex
[4] https://python.microbit.org
[5] https://learn.parallax.com/sites/default/files/content/Python/breadboard/mp4/bus-strips-verify-v-supply.mp4
[6] https://learn.parallax.com/sites/default/files/content/Python/breadboard/mp4/bb-voltage-zones.mp4
[7] https://cyberscope.parallax.com
[8] https://learn.parallax.com/tutorials/language/python/breadboard-setup-and-testing-microbit/set-power-circuits/cyberscope
[9] https://learn.parallax.com/sites/default/files/content/Python/breadboard/mp4/cyberscope-voltmeter.mp4