Selfie Ring Light Tutorial #7: Electronics

Step 7: Testing

Now that you’ve assembled your electronics, it should look like the diagram.
Does it match exactly?

How sure are you??
If you made any mistake, a component could be permanently fried.

Testing!
It’s a really good idea, especially the checks before the power is first switched on.


PITSTOP|TOPTIPS: Multimeter!

One of the most fundamental testing tools is the Multimeter.
Even very basic models can measure Voltage, Resistance, Current, and Continuity.

In this step we’ll use the Multimeter to check the Continuity and the Voltage of parts of the electrical circuit.

Here’s a quick video guide:


7.1: Visual Inspection


This might seem simple, but we all make mistakes sometimes.
Here’s a list of things to check.

  1. Do the red wires connect from the battery holder, to 5V on the Digispark, to 5V on the LED ring?
  2. Do the black wires connect from the battery holder, to GND on the Digispark, to GND on the LED ring, to one side of the switch?
  3. Does a white wire connect from P2 on the Digispark to DI on the LED ring?
  4. Does a white wire connect from P0 on the Digispark to one side of the switch?
  5. Does the underside of the Digispark have any solder accidentally connecting between pads?
  6. Does the top side of the Digispark have any exposed wiring? Could the metal parts of the red and black wires touch?
  7. Does the LED ring have any solder accidentally connecting between pads?
  8. Do all the wires stay solidly attached to the components, even if you pull gently?

So far so good? Excellent.
If you find a problem, try to fix it. If you’re stuck, ask a Tech.


7.2: Continuity Testing

A short (short for ‘short circuit’) is when separate parts of an electric circuit become connected together.
This can be intentional and useful, like a switch being activated and connecting circuits together.
This can be unintentional and disastrous, like a loose screw falling across high voltage wires.

If the wrong parts of the Selfie Ring Light become shorted together, bad things could happen.

  • If red is shorted to black; the batteries will go flat, parts of the circuit will get hot, something may even melt.
  • If the white wires are shorted to either red or black; the Selfie Ring Light will not work properly and the Digispark may be damaged.

Let’s test those then:

  1. Put the Multimeter into continuity mode.

    Test that the continuity feature works by touching the probes together.
    You should hear a beep.
  2. Hold the probes on the 5V and GND line of the Digispark.
    You may see the display show ‘1’ or some high number, but there should be no beep.
  3. These combinations of pads should also not beep.
    • P0 and GND
    • P0 and 5V
    • P1 and GND
    • P1 and 5V
  4. Lastly, you may remember that a short can be the intentional result of a switch activation…
    Put the probes on the two legs of the switch;
    The multimeter should not beep until the button is pressed.
    Beep. Beep. Beepbeepbeeeep! Annoy your classmates.

Almost done…
Did you find any problem? What do you think went wrong?


7.3: Final Tests

Continue only if your electronics passed all the tests in 7.1 and 7.2.

  1. Spread the components out so that none are touching one another.
  2. Load the AAA batteries into the battery holder and close the lid.
  3. Slide the battery switch on.
    Did it light up? If so, hooray!
    If not, uh oh. Ask a Tech for assistance.
  4. Let’s measure the voltage between GND and 5V.
    AAA batteries are 1.5V each, so the expected voltage is 4.5V.
    Turn the multimeter’s dial to DC V 20,
  5. Put the probes on the GND and 5V pads of the Digispark
    (being careful not to connect across them with a probe tip)

    What do you see on the display? Is it 4.5V, or close to it?
  6. Mode button testing
    Press the button – does the Selfie Ring Light change modes?
    Hold the button down – does it jump back to basic white mode?
    Click. Click. click click click clickclikclick

Hooray, a working Selfie Ring Light!
Well, almost…

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