Circuit to lower Sine wave frequency - Page 1
Forum section: electronics / beginners

author: Alfgan
author_rank: Contributor
timestamp: October 31, 2019, 08:14:18 pm
content: Hello everyone!I have a question. Is there a circuit or component or chip that lowers sine wave frequency?For example I wave a supply of 100Hz 20V sine wave and I need 40Hz 20V sine wave... what circuit or component would make it possible?ThanksHave a good day!

author: jhpadjustable
author_rank: Frequent Contributor
timestamp: October 31, 2019, 09:31:06 pm
content: For what purpose?

author: ogden
author_rank: Super Contributor
timestamp: October 31, 2019, 09:43:46 pm
content: Quote from: Alfgan on October 31, 2019, 08:14:18 pmSystem containing rectifier + inverter would do the job. Not trivial "circuit" at all.

author: Alfgan
author_rank: Contributor
timestamp: November 01, 2019, 09:08:36 am
content: I was only interested if it is possible.

author: ratatax
author_rank: Regular Contributor
timestamp: November 01, 2019, 10:17:07 am
content: An approximation could be to saturate the sine wave to make it square, then use a flip-flop to divide its frequency by 2 and smooth it to make it look sine again (will probably be a bit dirty though, and it's for signals, not power)

author: Twoflower
author_rank: Frequent Contributor
timestamp: November 01, 2019, 10:22:49 am
content: Depending on the requirements (power, stability, ...) a motor-generator system would be an option. But with the little information it's not easy to provide a viable solution.

author: mikerj
author_rank: Super Contributor
timestamp: November 01, 2019, 01:53:52 pm
content: Quote from: ratatax on November 01, 2019, 10:17:07 amThat would get you 50Hz rather than 40Hz.Assuming this is to provide power to something then converting the DC and generating a 40HZ AC is likely the only practical way of doing this. If these were high impedance signals then you could use a mixer along with a fixed 140Hz signal to downconvert the 100Hz to 40Hz, or you could do it with a PLL and fractional N divider.

author: rstofer
author_rank: Super Contributor
timestamp: November 01, 2019, 03:49:46 pm
content: Without knowing the load, it isn't even possible to suggest a solution. It might be fairly easy to do this kind of thing with a phase-locked-loop, at signal levels, and it might be easy to do with a motor-generator, at power levels. The recitifer-inverter solutions might be fine for power levels.There is a world of difference between the solutions.

author: grifftech
author_rank: Frequent Contributor
timestamp: November 01, 2019, 05:37:53 pm
content: rectifier, amplifier, MP3 player

author: KMoffett
author_rank: Regular Contributor
timestamp: November 01, 2019, 05:55:16 pm
content: Just a thought design:Phase lock loop to multiply 100Hz x 4 for 400Hz. Follow with a digital divide-by-10 for a 40Hz square wave. Through a very narrow 40Hz bandpass filter. Then amplify to need level.

author: Audioguru again
author_rank: Regular Contributor
timestamp: November 01, 2019, 06:05:16 pm
content: Many people use a switched capacitor multiple order lowpass filter IC to convert a squarewave to a pretty good sinewave.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 01, 2019, 07:55:59 pm
content: One could first set up the frequency (e.g. a via PLL or nonlinear multiplier) and than use that clock to generate a sine from a look up table or the like.Chances are the amplitude information would get lost.Another option would be a mixer (or 2) to shift the frequency by a constant amount.

author: rstofer
author_rank: Super Contributor
timestamp: November 01, 2019, 08:48:12 pm
content: We still don't have an answer to milliwatts of megawatts.

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: November 01, 2019, 09:27:14 pm
content: Quote from: Alfgan on October 31, 2019, 08:14:18 pmthese circuits are commercially available as "variable frequency drives" for basically all powers from kW to MW. if you just need a couple of watts, you could use your hifi amplifier. the basic principle is always the same1. take what you have and rectify / filter it to DC2. take the DC and power a halfbridge/fullbridge with it3. control the output of the bridge by applying a control signal of your choice (waveform, frequency, amplitude).OTOH,if you want to consistently change input frequencies (that is, 100 Hz to 40 Hz, 500 Hz to 300 Hz and so on) you could feed the (heavily attenuated) input signal into a device that is called a "harmonizer", something like the old "Ibanez HD1000", or the famous Eventide harmonizers. and then feed it into an amplifier to boost it back to the desired level.

author: IconicPCB
author_rank: Super Contributor
timestamp: November 02, 2019, 07:43:15 am
content: Google Cycloconverter

author: soldar
author_rank: Super Contributor
timestamp: November 02, 2019, 10:03:27 am
content: Quote from: rstofer on November 01, 2019, 08:48:12 pmNot only that but it needs to be clarified whether he is just trying to get 40 Hz or whether the 40 Hz needs to be in sync with the original frequency. Because they are radically different problems.

author: Zero999
author_rank: Super Contributor
timestamp: November 02, 2019, 02:28:03 pm
content: Use a fullwave rectifier to get 200Hz, divide it by 5 to get a 5Hz squarewave and pass it through a low pass filter to convert it to a sine wave.

author: SparkyFX
author_rank: Frequent Contributor
timestamp: November 03, 2019, 03:40:50 am
content: Getting a 40Hz in sync with 100Hz is unfeasible, unless it needs to start synced or so, but then its just as good as triggering a second source.

author: bob91343
author_rank: Super Contributor
timestamp: November 03, 2019, 06:11:14 am
content: Use an electronic piano keyboard. The lowest E (on a full keyboard) is close to 40 Hz.

author: jeroen79
author_rank: Frequent Contributor
timestamp: November 03, 2019, 03:32:27 pm
content: Quote from: Alfgan on November 01, 2019, 09:08:36 amThen the answer is "Yes".But if that is all you want to know and you have no actual application for this then there is little use in coming up with an actual "circuit to lower a sine wave frequency".