Multi-Tapped Inductor for Frequency Meter?

I'm looking to make an ultra-miniature 8-range frequency meter for the audible frequency range.

I am going to apply an amplified AC signal to the meter input, and was thinking on using a multi-tapped inductor with a capacitor on each leg to light an LED. There would be eight different legs on this setup for eight different frequency ranges.

I was also striving for maximum miniaturization, as the device should easily be held in the hand or clipped to a toolbelt.

Would it even work like I think it would? What would be the best way to get this thing as small as possible?

[EDIT] A side note - after rectifying does RMS increase or decrease with frequency? I could perhaps design or use a frequency controlled amplifier to drive an analog meter :green:

That's a pretty Rube Goldberg way to implement a frequency meter in this day and age. Why do you wanna do it that way, and what exactly are you trying to measure?

Being the sad, sad geek that I am I am looking to make a tap off my lighting coil (pre rectifier) and use the AC from the engine to make a tach for my bike. I am also looking into converting the speedo too. I'm thinking about a photocell/rotating disc driving a VU for that.

Converting to all-LED lighting to save on loading.

Here's the final geek twist: I'd love to use VU meters as my tach and speedo :roll: thus making the dashboard on my bike to look like a mic pre.

The bike kinda looks like this, but the stock gauges are quite large:



A couple of VUs I like. Sure it'd be easier to just print out a couple of gauge faces that look like VU meters, but what fun is that? I have six months of winter to look forward to working on this stuff. Calibrating will be a bitch.





:guinness: :guinness: :guinness: :guinness: :guinness:

> make a tap off my lighting coil (pre rectifier) and use the AC from the engine to make a tach for my bike.

Belt slip? I guess no belts on bikes.

That'll work. But tachometers that tap off the points (you got points? Or any low-volt spark signal?) are (or were) plentiful. Pop Lectronics ran that article over and over. Shocked that Google isn't finding a copy. R-C-R to shape the wave, unijunction transistor, R-C, analog mA meter. Power consuption is zero when off and a mA at 10,000RPM. You can use a 555 or other chips, but it is just more parts, more power.

> converting the speedo too

Speedo? Who needs that? My Jeep never had a working speedometer. I hold my Accord at 2,700RPM in 5th on the highway.

> all-LED lighting to save on loading.

I should think a 1,000cc Four could spare the tenth-horsepower of headlight and tail light. Dash lights are insignificant. You probably start that luxo-bike with a battery? The battery self-discharge may be greater than all your instrument lamps total. (My BSA had zero battery self-discharge: most of the time I didn't have a battery in it. Lucas electrics work better without juice.) Chuck the starter battery and the dynamo and the lights, you save 50+ pounds and gain 0.5% power.

Drum brakes can have less drag than disks, and you got near as many disks as my Accord. A couple of the drums from my Jeep would give about zero drag, and still stop that bike (once). (You would gain 50 pounds of rusty iron....)

> Calibrating will be a bitch.

For the neighbors, maybe. The idea is simple. A proper tach circuit is dead-linear for any practical purpose. Your "VU" meters have "%" scales. Leave the stock tach connected. Hold the engine at 8,900 RPM or whatever is "max". Trim the "VU tach" to "100%". Now when you look down and see "37%", you simply figure 37% of 8,900 and right away ya know ya doin' 3,293RPM.

You could figure RPM into audio tone and calibrate silently with your signal generator, but where's the fun in that? A 4-stroke 1-banger turning 3,600RPM is 30Hz. (Unless it is a dead-spark ignition with a second spark in the overlap.) A 2-stroke V-12 (R-R Crecy) at 5,00RPM is 1KHz. Heck, you don't need no signal generator: 60Hz is 3,600RPM on a 4-stroke 4-banger.

My 1-banga Beezer woulda shook the guts out of those 50-cent plastic meters in a mile.

Bypass any/all regulation in your dynamo, disconnect all loads. Voltage is a linear function of RPM. If it squeaks 10V at 600RPM, then 100V means 6,000RPM.

Do what my lawnmower did. Put a paddle near a rotating part. The wind blows it away, a spring resists it. The deflection is some function of RPM. Put a pointer on the paddle shaft.

I'm glad that there are gearheads here~!

BTW the bike is a 1978 KZ1000 Kaw. Yes, points.

Sounds like I have to find a heavier VU for the project. I'd like to use one of those narrow horizontals from the old reel-to-reels with an LED backlight that matches the paint.

I found a couple of links, I hope to digest all of this when I get a minute to sit down and read:

http://www.niksula.hut.fi/~mdobruck/siililand/mini/diy/alien/tacho/tacho.html

http://www.classictiger.com/techtips/motach.html

:!: