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RPM Counter connections

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Gordon Tarling13/11/2015 12:10:20
181 forum posts
4 photos

Has anyone here fitted one of these tachos to one of their machines? I received onelathetach1.jpg recently, but the connections on the display are labelled in Chinese and the seller isn't being very helpful.

Edited By Gordon Tarling 1 on 13/11/2015 12:10:51

John Rudd13/11/2015 12:52:36
1450 forum posts
12 photos


Have a look here.....

Looking at the rear of the tacho,(pcb side) the white connector numbered 1-5 left to right...

1) 12v dc positive supply

2) 12v dc ground

3) Signal input

4) No connection

5) Test +

the probe wires connect:


Blue- terminal 3

Black- terminal 5

Info offered on an as is basis, no responsibilty for blowing it up...wink

Hope this helps.....

The Merry Miller13/11/2015 14:23:40
484 forum posts
97 photos

Gordon and John,

I too purchased one of these Tacho's and it came with no wiring info.

After pressing the vendor eventually received this comprehensive diagram.

hall sensor.jpg

Thinking that this was less than useless I pressed them again and received the next bit of info as under.

chinese wiring diagram.jpg

I thought now this is much better and decided to take up a course as a Chinese interpreter before pressing them again.

I subsequently received the diagram as under together with a pleading request from the vendor to leave them "positive feedback"

wiring diagram.jpg

Well this enabled me to wire up in a fashion after interpreting what I thought they meant and guess what, it didn't work.

Any helpful suggestions would be appreciated apart from dumping it !!!

Len. P.

ian j13/11/2015 14:55:44
308 forum posts
336 photos


Just by coincidence I received one of these this morning from Hong Kong. Spent some time trying to work out the wiring , with no luck. When I came in for lunch I saw John's reply. When I wired mine up as John's ( Apart from I think he meant BLUE OF THE SENSOR TO TERMINAL 2 Ve Gnd ) info. it worked o/k.

Terminal 1 +ve to display and sensor (brown)

Terminal 2 -ve to display and sensor (blue)

Terminal 5 input from sensor (black)

Terminal 3 & 4 not used

That's how it is on mine.

PS just checked Terminal 2 & 3 on mine are communed together so are both -Ve in. So John's info is correct.



Gordon Tarling13/11/2015 15:01:16
181 forum posts
4 photos

Thanks for the help chaps. I'm pleased to say that John's connections appear to work - the display is live, there's a small red light visible in the back of the sensor and waving a magnet about in front of the sensor produces some numbers on the display. I now need to find a way to fix the magnet on the shaft in the lathe and fit all the other bits in place.

Len - have you connected yours as per John's details?

ian j13/11/2015 15:09:40
308 forum posts
336 photos

Gordon. Len must have pressed "add posting" while I was still composing my post smiley

Any way pleased you are up & running.


The Merry Miller13/11/2015 15:40:49
484 forum posts
97 photos


Mine was connected as John's. just went out to double check and confirmed it.

Still no display, I now assume that the display is duff.

It's too much bother to send it back.

Thanks all.


EdH13/11/2015 15:58:17
46 forum posts
27 photos

Interesting to see that there is another way to wire it up than the one I used.

I got some info from here:


(note spelling mistake so cut & paste)

and some more from here:


The wiring is marked on the PCB. With the connector on the bottom, the 5 pins are left to right

1 2 3 4 5

[Sensor Power +5V] [Sensor O/P] [Sensor GND] [Supply +12V] [Supply GND]

Ignore the dot, dashes and plus signs on the cable as they are different on all the ones I’ve seen.

My version is :

1 2 3 4 5

Sensor O/P not used not used Supply +12VDC Supply GND

This may be wrong as there is a small plus sign on the right of the characters on pins 1 & 5 or is that part of the character? Anyway mine work ok.

On the 5002C Hall Effect Proximity Detector I also have two wiring versions from the small label on them, one shows

a pull-up resistor to positive and the other to negative, I used a 220 Ohm resistor to positive.

I am using a Regulated 12VDC 0.5A power adaptor .

The Sensor is polarity conscious so get the magnet the right way round. I have used a bigger countersunk magnet on the Myford and screwed it on the pulley in one of the balancing holes (Oops!) and the one on the VMC Mill just relies on the magnetism as it sits in the recess under the spindle pulley so can’y fly off at speed. There is a screwhead down behind the pulley on the Myford so the magnet and retaining screw need to be slim to miss this.

I have put a variable speed setup on my Myford so no longer know what rpm it is running at and needed a way to monitor this so I put the magnet on the pulley inside the casing so this only indicates the direct drive

RPM so I will have to do a calculation to show what the direct drive RPM should be when running via the

back gears, I couldn’t think of a way to monitor the spindle directly so had to use this method for now.

EdH13/11/2015 16:00:13
46 forum posts
27 photos

Sorry but my tabbed numbers did not work out as I hoped , hope it still makes sense.

EdH13/11/2015 16:20:24
46 forum posts
27 photos

I have added some photos in my Albums under "4 Digit Tacho" if you want to see a scruffy installation but it does work.

Gordon Tarling13/11/2015 16:26:27
181 forum posts
4 photos

Len - the display should show all zeros if you just connect a power supply to it - if it doesn't do that, then I'm sorry to say that it's probably a duffer. However, it's certainly worth letting the seller know, as they may not want you to return the duff one.

EdH - very helpful, thanks.

Martin Cottrell13/11/2015 18:33:20
297 forum posts
18 photos
Posted by Gordon Tarling 1 on 13/11/2015 15:01:16:

Thanks for the help chaps. I'm pleased to say that John's connections appear to work - the display is live, there's a small red light visible in the back of the sensor and waving a magnet about in front of the sensor produces some numbers on the display. I now need to find a way to fix the magnet on the shaft in the lathe and fit all the other bits in place.

Len - have you connected yours as per John's details?

Hi Gordon, I used a small dab of silicone sealant to fix my magnet to the rear of the lathe spindle then left overnight to set. It has remained firmly in place for about 18 months now, resisting the urge to break free at occasional speeds in excess of 1500 rpm. I initially used a blob of blue tak and very slow rpm to test it and found by accident that there seems to be a right and a wrong side of the magnet to present to the face of the sensor, so if you find it initially doesn't read, try flipping the magnet over!


Gordon Tarling13/11/2015 18:43:31
181 forum posts
4 photos

Martin - noted, many thanks for that.


John Rudd13/11/2015 19:02:20
1450 forum posts
12 photos

There seems no consitancy to the wiring....but my description is as per the sketch in the ebay link I gave and marries up with that posted by the merry miller...

Oh and yes the probes are polarity sensitive to the you guys have found out...

Electronics is fun....well at times is is when everything works as anticipated...

Len, hope you get sorted...

Edited By John Rudd on 13/11/2015 19:03:20

The Merry Miller14/11/2015 10:06:48
484 forum posts
97 photos

Not a glimmer from the display when just hooked up to the PSU

Trying to contact the original seller in China through Ebay is a mammoth task so I've given up on that one.

What I'm going to do is make a calibrated dial using a laser tacho/rev counter and attach that to the mill control unit.


P.S. I haven't really given up on the display.

I'll try again later to see if he will replace it without me posting the duff one back to him, it's just making contact is the problem.

Len. P.

Steve Withnell14/11/2015 10:17:17
843 forum posts
222 photos

Are these things worth bothering with? I DIY'd one a few years back, but never bothered with a permanent install as it felt like an ornament rather than adding any value.


Michael Gilligan14/11/2015 10:24:09
20182 forum posts
1053 photos

Given that this thread covers an item mentioned in another recent discussion ... I think it worth referencing:



ian j15/11/2015 13:12:39
308 forum posts
336 photos

pb151427.jpgJust thought I would show how I mounted the sensor & magnet on my ML7R this morning,


Douglas Johnston15/11/2015 14:25:03
767 forum posts
34 photos

Well well- I got an identical item yesterday and was also puzzled about the connections so all this information is invaluable. I was amazed at the tiny cost of this item, including postage from China, how do they do it and still make a profit?

It is a pity the sensor is as large as it is, making it difficult to fit in the place I had in mind, so I will have to think about that and see if I can find another location to mount it.

What a wonderful site this is as it can now read my mind and fix my problems before I even ask for help.


Howi15/11/2015 14:51:10
359 forum posts
19 photos

There ate thousands of these on eBay, mostly the same module, quite a lot do include a wiring diagram in the listing.

It is not rocket science, 

On mine, when power attached does a self test and comes up with a code on the display before resetting to all zeros.

It will work on any voltage from 5v, not sure of max but plenty high enough, I just used a 9 v wall wart - half an amp should be more than enough.

Hall effect sensors are polarity specific, the magnet to sensor will only work one way, if the sensor light does not come on, just turn the magnet round.

The magnets supplied are very strong super magnets, mine is attached to the mill spindle just by its magnetism, mill will go to 2500 rpm, has not come off yet and highly unlikely to.

With regards to non working units, just let eBay know if you can't contact seller ( I have had no problems with contacting Chinese sellers and Will usually just send you a new one - they do NOT want any negative feedback so you should not have a problem getting a replacement.

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