At what age did you begin learning about electronics? What was the state of the art available to you at the time and what kinds of things were you building? For each reader these answers can be wildly different. Our technology advances so quickly that each successive generation has a profoundly different learning experience. This makes it really hard to figure out what basic knowledge today will be most useful tomorrow.
Do you know the forward voltage drop of a diode? Of course you do. Somewhere just below 0.7 volts, give or take a few millivolts, of course given that it is a silicon diode. If you send current through a 1N4148, you can be pretty certain that the cathode voltage will be that figure below the anode, every time. You probably also have a working knowledge that a germanium diode or a Schottky diode will have a lower forward voltage, and you’ll know in turn that a bipolar transistor will begin to turn on when the voltage between its base and emitter achieves that value. If you know Ohm’s Law, you can now set up a biasing network and without too many problems construct a transistor amplifier.
The RFID circuit only uses two of the ATtiny’s pins and neither of which is the ground or power pin. The ATtiny is equipped with protective diodes on its input pins, and if you apply an AC waveform to the input pins, the chip is able to use the leakage current to power itself. Once that little hurdle is crossed, the ATtiny can do the rest of its job handling the RFID circuitry.
This project takes a deep dive into the internals of the ATtiny. If you’ve ever wondered what was going on inside of everyone’s favorite tiny microcontroller, or if you’re looking for an RFID circuit that keeps parts counts to an absolute minimum, this is the project for you. The ATtiny is more than just a rugged, well-designed chip, though. It’s capable of a lot more than such a small chip should be able to.
[Kevin Darrah] is risking the nerves on his index finger to learn about ESD protection. Armed with a white pair of socks, a microfiber couch, and a nylon carpet, like a wizard from a book he summons electricity from his very hands (after a shuffle around the house). His energy focused on a sacrificial 2N7000 small signal MOSFET.
So what happens to a circuit when you shock it? Does it instantly die in a dramatic movie fashion: smoke billowing towards the roof, sirens in the distance? [Kevin] set up a simple circuit to show the truth. It’s got a button, a MOSFET, an LED, and some vitamins. When you press the button the light turns off.
He shuffles a bit, and with a mini thunderclap, electrocutes the MOSFET. After the discharge the MOSFET doesn’t turn the light off all the way. A shocking development.
So how does one protect against these dark energies out to destroy a circuit. Energies that can seemingly be summoned by anyone with a Walmart gift card? How does someone clamp down on this evil?
[Kevin] shows us how two diodes and a resistor can be used to shunt the high voltage from the electrostatic discharge away from the sensitive components. He also experimentally verifies and elucidates on the purpose of each. The resistor does nothing by itself, it’s there to protect the diodes. The diodes are there to protect the MOSFET.
In the end he had a circuit that could withstand the most vigorous shuffling, cotton socks against nylon carpeting, across his floor. It could withstand the mighty electric charge that only a grown man jumping on his couch can summon. Powerful magics indeed. Video after the break.