CircuitLens Journal

Short electronics articles, one a day, with worked examples and bench tips.

• 2 November 2026Zener Diodes as a Voltage Reference: What They Do Well and Where They Fall ShortA Zener diode and a resistor make a quick reference rail on the bench. Here is how to size it with real numbers, and where its drift and loading limits will bite.
• 1 November 2026What a Flyback Diode Protects, and Why It Sits Across the CoilA flyback diode across a relay or solenoid coil stops the large voltage spike that appears when the current is switched off. Here is how it works and how to size and place one.
• 31 October 2026BJT vs MOSFET as a Switch: Choosing the Right One at the BenchA bench-focused comparison of how bipolar transistors and MOSFETs behave as switches, with a worked example driving a 100 mA load from a 3.3 V microcontroller pin.
• 22 October 2026Why a Diode's Forward Voltage Isn't One Fixed NumberThe 0.7 V rule of thumb hides a real spread. Current, temperature, and diode type all shift the forward drop, and a worked example shows how much it matters on the bench.
• 21 October 2026Reading a MOSFET Datasheet: Vgs(th) vs the Gate Voltage You Actually ApplyVgs(th) is where a MOSFET just begins to conduct, not where it switches fully on. Here is how to compare it with the gate voltage on your bench and avoid a part that runs hot.
• 20 October 2026Why a Crystal Oscillator Needs Load Capacitors to Hit Its FrequencyA crystal's rated frequency assumes a specific load capacitance. Here is how the two capacitors around it set that load, with a worked example and bench checks.
• 19 October 2026Inductors Resist Changes in Current, Not Current ItselfAn inductor does not oppose current; it opposes how fast current changes. That one idea explains coil kick, slow turn-on in circuits, and why a switch can get zapped.
• 17 October 2026What ESR Means for a Capacitor and Why It Matters in Switching SuppliesEquivalent series resistance decides how much a capacitor really smooths a switching supply's output. A worked example shows why a cap that looks fine on paper can still ripple badly.
• 16 October 2026Reading a Resistor's Colour Code Without a Chart: The Logic Behind the BandsOnce you know the pattern, a resistor's colour bands can be decoded in seconds. Here is the reasoning behind the code, a worked example, and bench habits that prevent misreads.
• 16 October 2026Electrolytic vs Ceramic vs Film Capacitors: Picking the Right DielectricElectrolytic, ceramic, and film capacitors look interchangeable on a breadboard until they aren't. Here is how their dielectrics change capacitance, polarity, loss, and stability.
• 27 September 2026Why Decoupling Capacitors Sit Close to the IC, Not Just 'Somewhere on the Rail'Placement matters as much as value: a decoupling cap a centimeter too far away can fail to do its job because of the wire it's connected through.
• 26 September 2026How a Multimeter Actually Measures Resistance (and Where It Can Mislead You)Your meter doesn't sense resistance directly—it injects a tiny current and measures a voltage. Knowing this explains most of the odd readings you get in-circuit.
• 25 September 2026Ohm's Law in Practice: Reading a Resistor Under Real-World TolerancesOhm's Law gives you a clean prediction, but real resistors and meters wander from the ideal. Here's how to account for tolerance without second-guessing your bench work.