Category Archives: colpitts oscillator

Crystal Oscillators Explained

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We’ve read a lot about oscillators, but crystal oscillators seem to be a bit of a mystery. Hobby-level books tend to say, build a circuit like this and then mess with it until it oscillates. Engineering texts tend to go on about loop gains but aren’t very clear about practice. A [circuit digest] post that continues a series on oscillators has a good, practical treatment of the subject.

Crystals are made to have a natural resonant frequency and will oscillate at that frequency or a multiple thereof with the proper excitation. The trick, of course, is finding the proper excitation. …read more

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A Radar Module Teardown And Measuring Fan Speed The Hard Way

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If you have even the slightest interest in microwave electronics and radar, you’re in for a treat. The Signal Path is back with another video, and this one covers the internals of a simple 24-GHz radar module along with some experiments that we found fascinating.

The radar module that [Shahriar] works with in the video below is a CDM324 that can be picked up for a couple of bucks from the usual sources. As such it contains a lot of lessons in value engineering and designing to a price point, and the teardown reveals that it contains but a single …read more

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A Graph Plotting Metal Detector

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Metal detectors can be a great source of fun, and occasionally even found wealth. They allow the detection of metal objects at a distance, enabling hidden treasures to be discovered. They’re also highly critical to the work of minesweepers and unexploded ordnance disposal teams. [Andrius] wanted to add such a device to his kit when motorcycling through the woods of Lithuania, and thus decided to undertake a build of his own.

The detector is a thoroughly modern one – fans of the 555 may want to look away now. A Collpits oscillator, built from two transistors, is used to generate …read more

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The Colpitts Oscillator Explained

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The Colpitts oscillator is a time-tested design — from 1918. [The Offset Volt] has a few videos covering the design of these circuits including an op-amp and a transistor version. You can find the videos below.

You can tell a Colpitts oscillator by the two capacitors in the feedback circuit. The capacitors form an effective capacitance for the circuit (assuming you have C1 and C2) of the product of C1 and C2 divided by the sum of the two capacitors. The effective capacitance and the inductance form a bandpass filter that is very sharp at the frequency of interest, allowing …read more

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