Optical Tachometer

[sternwake]

I recently purchased this:

https://www.ebay.com/itm/Digital-Tachome...woV3BBEV2b&_trksid=p2332490.c100935.m2460

It came a few days ago and I took another day to unbox and test it.

One is supposed to cut off a reflective piece of tape, attach it to whatever is rotating, then Aim the device at it, where a 'laser' is supposed to reflect off the sticker and the device count the revolutions.

Mine has no red laser/LED
It reads zero.
I took my IR temp gun, which does have a laser, held it side by side with the unit, aimed it at reflective sticker, and then it reads the rpm.

The seller insulted me by saying perhaps I installed the battery backwards, which is impossible as the slots for the + and - of the 9v battery are different width, and/or they assumed I was just using it incorrectly, cant read directions, or cannot grasp simple concepts.

  I guess in this day and age they have to assume absolute overwhelming ignorance and vapid  stupidity of the consumer, and they'd be fools to assume otherwise, as just think how stupid the average person is, then understand half of the rest of them are even more so.

I was wanting this device primarily to see just how fast that 320 amps Leece Neville alternator is spinning via the Auxiliary drive pulley on the detroit diesel at idle, and of course fans, the Leece was the excuse to finally purchase.

I told seller I'm willing to try and fix it, but they better not assume I am a knuckledragging idiot who can't figure out how to press a button and aim a light at a spinning reflective sticker again.

If it worked as described I'd be pretty happy, and I can still make it work if I put my IR temp gun right next to it and aim its laser at the sticker.  Honestly I want to just fix it if possible, perhaps just a fractured or missing solder joint on the LED or laser.  Kind of doubt it is an actual laser, but I guess its possible.

I'm kind of interested to see just how much slower a dirty fan spins than a clean fan at the same exact voltage.  The tach opens up all sorts of new data collecting and potential experiments.

My balancing of fans is usually using a small piece of tape on the fan hub. The reflective tape for the tach might have to take over that task.  Should be interesting to see amp draw and rpm of a balanced fan vs unbalanced one at the same voltage.

All hail actual Data.

[Gr8ful]

Paypal will take care of you. Also give them bad feedback & they'll want it off & send a new one.

[sternwake]

Not at that stage, yet.

Gonna open it up see if there is anything obvious i can easily remedy, an action the seller authorized.

[Everyroadleadshome]

That will be some interesting new Data for you if you can resolve the issue. It's always so disheartening to be anxiously awaiting a new toy's arrival, only to have it crash when you realize you get the crappy broken one. I'd say what are the odds any one person gets the broken one out of tens of thousands produced, but those odds are probably actually pretty good in a world full of cheap manufacturing and little to no quality controls in place.

Im currently working on making some miter saw extension wings for a DeWalt stand I have. The idea came to me in bed one night, where I thought if I buy another set of removable brackets the stand uses to attach the saw to itself I can make some removable extension wings. I hop online and a pair of brackets are about $50 everyplace. Look on ebay and find a pair for 26. Think great, half price. I order them, anxiously wait a week til they arrive to see if my idea will even work and boom....only one stupid piece in the box. Contact seller and he says the listing was for only one piece. WTF.....they only work in pairs you idiot!! And no where on your listing did you say it was for only one.....everyone in the world is going to assume they come in pairs. So I guess that's what I get for trying to save twenty bucks. I can return it but that's going to cost 12 bucks in return shipping which I'll probably just do and buy them on Amazon and get the pair in two days. It's not so much the money as the time wasted.....been anxiously wanting to build this thing and now on day 8 and im no closer to starting it!

[rvpopeye]

It's the CROWS I tell ya !!!

[sternwake]

I can make this toy work, and there is no indication, yet, that  the seller is going to not replace it.

I did open it up.

The LED, (not  a laser, what a surprise!) does have a crappy solder joint, but I also put my voltmeter on the led's  legs, one of which has a + sign next to it, It read - 2.73 volts. NEgative.
I'd expect if it were fed 5v dc+ it would light up fairly brightly.  I think the LED's driving circuit is faulty.

I related this to seller, ball is in their court.

I don't see any point in reflowing the solder if the LED is getting fed -2.73v.
There are certainly e bay items which appear exactly the same, for twice the price.

  I guess the internals could be made to different spec's/quality, then  stuffed into the same casing.  I've seen that plenty with LED dimmers. which now have all been phased out in favor of voltage buckers instead, even the ones with what appear to be burlier components.

   

   

[Gr8ful]

I have one that works great. I have the old SW manual ones I used with the sawmill that have a couple different rubber tips. I had to use one to check the rpm of the '38 Taylorcraft at full speed. I went very slow & careful & when the digitals came to Harbor Freight years ago I bought one of the 1st. I think when some things are sold on ebay for 1/2 price they may be rejects the employees se or other companies sell knowing they're defective but it's going to the US so they don't care.

[sternwake]

Could be.

The seller is sending another one with 'hope' that it works

If it does not, I'm just going to wire up an LED to run off of the 9v battery directly.

[rvpopeye]

2 for the price of 1 plus an LED !

Sell the first one on ebay ....

[Blacktank]

so plastic chinese crap turned out to be plastic chinese crap?

a sellers feedback is far more important than a single transaction and most people are honest folk