quick, messy, & cheap spindle RPM meter / tachometer

[SG51Buss]

Just for fun, did an eBay search of 'bicycle speedometer'. OMG, over 4,000 items!
This one (about $3) caught my eye. Notice the large LCD number segments in the middle of the display, showing '188.8', where the speed would be displayed. If this thing could actually display as high as "199.9", might could work out as a tach by ignoring the decimal point. You program into these things the tire diameter or circumference, and choose MPH or KPH.

If you sit down and grind thru the math, realizing that you could attach more than one magnet, you may come up with a usable configuration...

 

[spaceman_spiff]

what about this:

http://www.ebay.com/itm/New-Hour-Me...r-Motorcycle-Boat-Bike-US-STOCK-/331086473062

It has an inductive pickup meant for ignition systems, but I bet you can figure out a way to trick or modify the input to work with magnet and reed relay or hall sensor type setup. Then you would get both an hour meter and tachometer that reads directly in RPM for the $15 range

 

[SG51Buss]

Now you're cookin'. That version uses a wire wrapped around a plug wire. I made a permanently mounted timing light for my hotrod using that inductive trick. I recall that getting 20v spikes was easy that way. Not sure if you can get that much with a magnet pickup. Time to experiment.

Tried "digital tachometer motorcycle" and found this thing, $7.55. It uses the grounding side of an ignition system, and will respond to 12v spikes.

Shame on you. Now I have to order one...

 

[SG51Buss]

Well, foo. So I tried just "digital tach" and these panel-mount things pop up. New item. Around $8.55. Triggering by proximity sensor or hall, up to 5v trigger. This is the way.

 

[SG51Buss]

Well, foo2. I can't stop. Tried "tachometer hall proximity sensor", and found the complete kit, with sensor and magnet, around $13.

 

[herbet999]

... which should put the frequency up into the audio range, and then you could try measuring it using a guitar tuner, or perhaps a computer with software that lets you measure frequency or look at the waveform and figure it out.

Did this in my college days. Used an oscilloscope to analyze the waveform created by a spinning mirror. All to measure the speed of light... Apparently my college days were pretty boring.

 

[spaceman_spiff]

Now you're cookin'. That version uses a wire wrapped around a plug wire. I made a permanently mounted timing light for my hotrod using that inductive trick. I recall that getting 20v spikes was easy that way. Not sure if you can get that much with a magnet pickup. Time to experiment.

Tried "digital tachometer motorcycle" and found this thing, $7.55. It uses the grounding side of an ignition system, and will respond to 12v spikes.

Shame on you. Now I have to order one...

SICK. That is perfect looking for an old lathe too....if you get that up and running I betcha there will be a few others doing the same!!

 

[spaceman_spiff]

Well, foo2. I can't stop. Tried "tachometer hall proximity sensor", and found the complete kit, with sensor and magnet, around $13.

(stands up)

(clap clap clap)

well done. Not as cool looking as the gauge one but if if its that cheap and ready to go, its a winner.

now I just need to add a variable speed drive to my lathe to go with my tachometer lol

 

[SG51Buss]

Well, I just couldn't let this go. Decided to shop around some more, mostly looking for much smaller components. Found and ordered a digital tach, 2" x 1", hall sensers and magnets. These should be small enuff to squeeze into a 6" lathe. Naturally, won't see this stuff for at least a month, so that'll be for a future project thread.

 

[Rick Leslie]

This is a subject I keep coming back to. I have a gaping hole in the headstock of my mill where the factory tach once rested. I want to fill the space with a modern version but I understand little about the differences in the pick-up methods. The magnetic pick-up I get, but how does the Hall Effect work? Does it use gaps or grooves in the pulley surface for reference?

Magnets on my lathe spindle wouldn't be a problem, but I don't want them on the mill. If the detach, it could cause all kinds of mayhem in the gear box. I much prefer the grooved pulley method. Or am I just completely misunderstanding the concept? Sorry for the side track.