Responding To Your Comments About The Frequency Counter Video!!

"Nu-cu-ler!" (eye starts twitching with flashbacks to the George W. Bush era)

Circuitmike

I though so. The reeds don't vibrate because of a vibrating magnetic field but the coil with an input electrical frequency causes an armature to oscillate which in turn causes the reeds to MECHANICALLY vibrate to their individual natural frequencies. See post of the design on the community page.

The vibrating reed frequency meter The vibrating reed frequency meter, also called the Frahm frequency meter after its inventor, Hermann Frahm (Daffron & Greenslade, 2013), comprises a graded set of tuned metal reeds, typically 11 or 21, which are arranged to vibrate in response to an oscillating magnetic field or mechanical vibration. They are rugged analogue instruments useful for measuring the frequency of a mains supply or an engine’s rotational speed, and are still available today even though digital devices have largely supplanted them. Frahm frequency meters are essentially a side-by-side array of tuning forks which operate on the principle of mechanical resonance (Bakshi & Bakshi, 2009; Hicks, 1998). A simplified diagram is shown in Fig. 1, where 11 reeds ranging from 55 Hz to 65 Hz are shown (Fig. 1B). When the reeds are mechanically excited at a certain frequency, say 60 Hz, the reed with matching natural frequency will tend to vibrate the most. In practical terms, if the instrument is to measure the frequency of the mains supply, a coil is used to generate an oscillating magnetic field which in turn attracts a soft iron armature, producing an oscillating mechanical force on all the reeds (Fig. 1A). Incidentally, because the alternating current creates magnetic attraction twice each cycle, the reeds are actually tuned to double the indicated frequency. Devices designed to measure engine speed are held directly against the engine, in which case no scaling is necessary. The instrument’s dial is an end-on view of the reeds, and the reed vibrating with the highest amplitude indicates the frequency of the supply (Fig. 1C). Simplicity and robustness are the instrument’s major attributes.

I love watching you work through your discovery and understanding in these videos. Thanks!

C Genco

Impedance, current, and voltage demands dictate this set up to be able to drive the meter.

Fran Blanche

Can't a music player or just a computer produce sine waves? It's enough to drive a speaker, why not this? (Maybe i should have listened better)

Jasper

This showed up in my YouTube feed. LOL https://www.youtube.com/watch?v=xJGsVrs9El8

Reminds me of Marty going into Doc Brown's lab from Back To The Future. Sounds like it's going to explode when you crank up the frequency!

The title of this video should be "Demo of the frequency meter". I almost turned it off halfway because I thought you were just going to quote comments and talk about why all the suggestions wouldn't work. Thanks for posting! High quality content as usual.

Jac Goudsmit

Hi Fran, thank you for sacrificing your day off to satify us annoying "customers". I fully agree with your learning method of working things out rather than asking Dr Google. However I have to confess that sometimes due to time constraints I do cheat or ask my assistants, young minds seem to store so many facts!

Dr Andy Hill

Good one thanks Fran, your music talent is finally emerging.

Frantastic!

nj Phil

Sine vs. square didn't cross my mind, but as soon as you said it I kicked myself for not realizing that's why this can't be solved with a rectifier, a 555 + pot, and a MOSFET 😂. Thanks for humoring us out here in the peanut gallery!

Travis Snoozy

Fran, THANK YOU for explaining the power transformer issues. And your creative audio transformer solution was truly inspiring! This touches on a subject that I used to run into all the time with home flight simulator builders years ago. Some people who bought used aircraft instruments on eBay for home simulator projects figured there was no difference between 400Hz aircraft power and 60Hz home wall power. Well, some tried to substitute 60Hz for 400Hz with disastrous results. If there is any kind of input transformer inside the instrument, it will blow the primary coils. Sometimes quite dramatically. Therefore, trying to feed a 400Hz transformer with 60Hz will blow it up. Period! Feeding 400Hz into a 60Hz transformer will sort-of work, but the waveform and voltage on the secondary windings will be off. And, yes, I can imagine using a large MOSFET, or other power transistor, to stimulate one side of a transformer to get a desired output. That’s what they used to use for aircraft static inverters that converted 28VDC battery power into 115V 400Hz AC power. They’re extremely annoying as the buzz of the transistors and coils is louder than one might think. They also get hot and sometimes require loud fans. Whenever you board a commercial aircraft, you can almost always hear that 400Hz noise bleed through the aircraft’s PA system, or from devices under the floor, like 400Hz motors and blowers. Now they have solid state static inverters that use a bunch of high-powered MOSFETS to make the conversion without a noisy transformer. But when I was a kid, I had to learn the hard way that even though a 400Hz transformer will say “115VAC” input, it does NOT mean it will accept a 60Hz input. So, yes, I blew up a number of 400Hz transformers as a teenager until I understood WHY 400Hz was required and could not be substituted with 60Hz. Essentially, a 115V 60Hz transformer delivering 8 amps of 26VAC for the output will be rather large and heavy. A 400Hz transformer that does the same voltage step-down function can be as small as 1/4th the size and weight of its 60Hz cousin. And weight savings on aircraft is absolutely critical. The generators on the engines would be HUGE and HEAVY to generate AC power at 60Hz as opposed to 400Hz. I’m not sure of the science of electro-magnetics and transformer cores as it is a pretty specialized science. But your demonstration of the power transformer input impedance problem with interfacing with your amplifier really hit home. Hopefully you saved some people from blowing up their signal sources trying to reverse-drive a power transformer. And maybe my story here of blowing up 400Hz transformers will help somebody who is trying to get 115V 400Hz aerospace or defense electronics to work. Don’t repeat my early mistakes. Get a static inverter or power converter for 400Hz devices.

Matt Wietlispach

Well done Fran!

William E Lee

FRAN THE DEMO IS SO COOL!!

Jason Thorpe

Very Cool!

Agreed. Good vibrations all through the demo.

Rick Lett

The two freq meter episodes easily the most fun this year! and kudos for gently dissing some of your detractors. 73!

Rick Lett

I have a large number of vacuum tube audio power amplifiers from church organs. Their output transformers are massive because they needed to have good response down to around 20 Hz.

Drewski Brewski

I 100% use the same approach for "unknowns". And just because a person came to the same approach as was used in the meter does not mean it is the only way.

Drewski Brewski

thank you for explaining the impedance mismatch problem

BiggieJohn

Ha! No need to beat a dead horse, but maybe that "pickup" needs a permanent magnet!

Drewski Brewski

My favourite video of the year, so far!

David Peaker

Nicely demonstrated :D I love this meter. Well done on berating those who criticise too!