Advent Electronica #2

So what’s been behind the other 7 doors of our electronic advent calendar? After days 4 and 5 we’d collected some red insulated wire to create a basic switch and a 10 kΩ resistor to give a circuit with a total resistance of 11 kΩ (remember, our green LED has a built-in 1 kΩ resistor) meaning we should be able to save enough battery life — or ‘juice’ — to power our Christmas Eve experiment! I’m hoping it’ll look as bright as this image!


Day 6 was pretty exciting, I have to say, as behind this door was a tilt sensor. It consists of an open contact with a small metal bead sitting on top when the sensor is in an upright position. Tilt the sensor and the bead rolls off the contact, thus breaking the circuit. Vibrations can also cause the bead to jump up and down, intermittently breaking the circuit. First, we tried the tilt sensor, where an angle of ~80 degrees, extinguished the LED. Then, we pressed a vibrating mobile phone up against the sensor and the LED flashed in sync!

Day 7 gave us a red LED to add to our green one from day 3. We added the red LED into the tilt sensor circuitry: the red LED was constantly illuminated whilst the green LED would flash if the bead was no longer in contact. It would make quite a good vibration sensor, perhaps as an intruder alert!

We created another basic switch with the transistor behind door number 8 whilst a new resistor on day 9, this time 82 kΩ, extended our battery life to more than 6 months!

And here we are, at day 10, with another transistor for further current amplification. Using a finger, we can light the LED with the tiny amount of current passing through the digit using the an amplification of 250 times!

See you again next Thursday!

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Front and article image: “In the palm of my hand” by Scott W. Vincent. CC-BY 2.0.

Categories: JPhys+

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