Simplest circuit to get a full voltage reasonable current wave from oscillator - Page 1
Forum section: electronics / beginners

author: Infraviolet
author_rank: Super Contributor
timestamp: November 30, 2022, 08:32:30 pm
content: I've been looking in to oscillators and crystals for generating sine and square wave signals but wanted to clarify a few things. Particularly in regards to getting strong signals from them, wave going up and down to atleast close to Vcc(5V, 3.3V, whichever it happens to be) and Gnd, and having currents up to perhaps 100mA if needed for blinking an LED at a specific frequency, to then use elsewhere within circuit designs.Many crystals seem to be primarily intended for clocking a microcontroller, attach the two ends to specific pins on the microcontroller, and then attach capacitors of a certain approximate size from these ends to Gnd and they act to provide a clock. But if you want to use a crystal in a more customised circuit design this isn't much use.I've seen some analogue designs with transistors, resistors and capacitors aiming to get a signal out from an oscillator crystal, but they look like they'd be quite sensitive to inaccuracies in the resistor and capacitor's values. Surely the idea of crystals with high precision ratings for the accuracy of their frequency is that you can sidestep al worries over R and C accuracies?I've also seen some designs using a crystal with a pair of NOT gates, and think for these that the capacitor values used should be tolerant of inaccuracy, but can't quite understand why. Also these seem to be for square waves only, I'd like to know hw to construct sine and triangle wave alternatives too.I've seen some 4 pin oscillators for sale, usually with a Vcc, Gnd, enable and output pin. Are these a pretty rare component to use though, the kind which only comes in more unusual sizes from one or two manufacturers, the sort of part you can't often find generic substitues for? Also these all look pretty big in board space consumption, several times the size of a 2 pin crystal (even a through hole canned version). And again only give square waves it seems, not sines or triangles.Thank you

author: Zero999
author_rank: Super Contributor
timestamp: November 30, 2022, 09:00:47 pm
content: A crystal is just a type of resonator. An amplifier is required to make an oscillator. The crystal is connected in the feedback path of the amplifier, so it filters out all frequencies, other than the desired one, causing the amplifier to oscillate at the correct frequency. It's the same principle to acoustic feedback, when the microphone is placed too close to the speaker.Most crystal oscillator circuits these days output square waves, because the most common application is to clock a microcontroller, or similar logic circuit. It's possible to use a linear amplifier to make a sine wave, but is much easier to simply use an oscillator with a square wave output and add a filter to select the fundamental frequency, which will result in a sine wave. A square wave is a mixture of multiple harmonic frequencies of the fundamental.

author: Benta
author_rank: Super Contributor
timestamp: November 30, 2022, 09:45:33 pm
content: Here's a good example of an IC that simply works. Small, simple and easy. But it won't do 100 mA drive, 24 mA tops.https://www.nexperia.com/products/analog-logic-ics/control-logic/gates/combination-gates/series/74LVC1GX04.html

author: TimFox
author_rank: Super Contributor
timestamp: November 30, 2022, 10:44:59 pm
content: Quote from: Infraviolet on November 30, 2022, 08:32:30 pmBy nature, quartz crystal resonators ("crystals") are relatively insensitive to the exact capacitance and resistance of the circuit.If you look this up in a standard textbook, the equivalent circuit is usually a very large inductance in series with a very small capacitance, and a second capacitor in parallel with that series connection.Crystals specified for "parallel-resonant" frequency are specified by the manufacturer at a specific (low) external capacitance value (maybe 20 pF) in parallel with the crystal, and can be adjusted over a narrow frequency range by using a variable capacitor there.If specified for "series-resonant" frequency, that is essentially independent of any capacitance in series with the two-terminal device, but is not intended for an external parallel capacitance.

author: wasedadoc
author_rank: Super Contributor
timestamp: December 01, 2022, 09:34:17 am
content: If you want to blink a LED the frequency of a crystal oscillator will be much too high for a human (or any animal) to see it as blinking. Would need additional circuitry to substantially reduce the frequency.

author: Infraviolet
author_rank: Super Contributor
timestamp: December 01, 2022, 05:01:52 pm
content: Modulating optical data is a very good reason to be needing a fast blinking led, the faster your blinking the faster you can transfer data.