Thread: Wow - huge price difference

Mine will probably turn up next week while i'm away so i'll just have to wait.....Good to see that it worked well, 6 rpm, i think thats even slower than the Leblond will go! (13rpm i think?)

Martin,

I have a Hall sensor (two wires) and magnet from one of the treadmills.

How do I determine if it is suitable for this tacho ?

One lead has a dotted line down it and the other has a single unbroken line.

Rob

Originally Posted by nearnexus

Martin,

I have a Hall sensor (two wires) and magnet from one of the treadmills.

How do I determine if it is suitable for this tacho ?

One lead has a dotted line down it and the other has a single unbroken line.

Rob

Rob,
Does it have a code on it? All the HE sensors i have seen or used have 3 wires, V+ ground and a Data line. If it doesn't have a code on it the only other way to tell is with a oscilloscope. Don't be too worried, i ordered 20 so i'm sure i could send you one (at 15c each it won't break the budget)

I couldn't see any code on it - only the treadmill name.

Looking at the specifications on Ebay for the tacho and the various connections shown, am I correct in that the image on the far right under pin definition is for a Hall sensor?

If so, it only has two wires. Or have I got it wrong ?

As you can guess, I'm no whizz on this type of electronics

Rob

G'Day Rob,
It sounds more like a reed switch, especially if it operates with a magnet, Hall sensors are usually switched with an iron vane, as Ueee says Hall sensors usually have 3 leads. I am not sure if a reed switch would respond fast enough for a tacho application. I had a quick play today using a Sick reflective sensor with a single segment sector plate (1/2 reflective, 1/2 black) the display was perfectly stable, not even 1 RPM variation at any speed. So I am rethinking the Hall sensor. (I know I change my mind more often than a woman).
Regards,
Martin

Hi Martin,

You are probably right on that. Anyway I like the idea of the red LED tach, and it would be a lot easier to fit into my lathe head than the LCD job that's comming, so I too will buy one from Ebay - before the big 5% sale ends

Then when you have yours setup nicely I will buy the same bits to get mine going.

Update : ordered the red LED display.

Also rummaged around in my electronics stuff and found the bits in the attached photo which look to be a "real Hall sensor" and a sector disc

What do you recon guys ?

Rob

Originally Posted by nearnexus

Hi Martin,

You are probably right on that. Anyway I like the idea of the red LED tach, and it would be a lot easier to fit into my lathe head than the LCD job that's comming, so I too will buy one from Ebay - before the big 5% sale ends

Then when you have yours setup nicely I will buy the same bits to get mine going.

Update : ordered the red LED display.

Also rummaged around in my electronics stuff and found the bits in the attached photo which look to be a "real Hall sensor" and a sector disc

What do you recon guys ?

Rob

Ok. Hook, line and sinker! I've been watching this I you have sold me on the idea. I bought one last night with the massive 5% discount!

Rob, that notched signal generator and hall sensor looks the goods! Looks like it's more suited to a vehicle with ABS than for a lathe!

Lots of signals per revolution so you should get a nice stable reading to very low RPM's.

The reed switch option would be OK at low RPM but there would become a stage where the signal frequency generated by the notch would be too great for the switching speed of the reed switch especially with more notches (creating more pulses) per revolution. A hall affect sensor is the more elegant method of use.

Can't wait to get mine now!

Cheers,

Simon

I just bought one too.

Re the reed switch- my current tacho is a bicycle computer. It works well at the max RPM of the Hercus 260. Initially I will try the LED tacho module with the reed pickup from this setup to see how it goes. I agree that HE or optical is more elegant though.

Chris

Thanks Simon.

OK so which of the connection settings shown in the diagrams on the Ebay page for the tachometer are for a Hall sensor?

I suppose a multi edge notched metal disc would be just as good as the plastic job in the photo ?

While I had the camera going, heres a shot of how the dual cooling fans are being attached to the treadmill motor for the lathe conversion.

I could have made it round externally (rather than square) and used a big hose clamp to compress it, but used a bolt instead.

I machined up some recycled polycarbonate and clamped it to the motor as the fan mount. They suck air through the motor from the drive belt chamber and will run off the same 12v power pack as my new red tacho.

As polycard is a bit slippery, to make sure it stay's put I machined a groove on the inside clamping surface of the polycarb and used silicon between it and the motor and let it harden before clamping up.

Rob

If the wheel in the pic is plastic and part of the original use of the switch I would say that it is an optical sensor, but it should work. Yes the gar right pic is the one you need, but you have to work out which wire is which......

Your right Ueee. It's optical.

I found a parts list for the treadmill and it's definitely optical.

Rob

I'm getting rusty (not that I'm an expert!) yes now you mention it, it is an optical photo interrupt or sensor. They work just as good!

In regards to the notched pulse generator, any material is OK but dark or black in colour is always better. It reduces beam reflection and false triggering and hence potentially erratic display.

In terms of the pin out, most photo interupters are similar. They should not need too many external components to drive them, maybe a resistor or two as they generally have inbuilt transistors or op amps to buffer the output.

Do a search for photo interrupter. The one in the attached image just needs two resistors. The one on the output is there to clamp the output to digital 0 in the absence of a signal. This stops the output from "floating" if there is no signal (beam is blocked). This ensures that the output is either 0 or Vcc and nothing in between.

In terms of resistor values. The resistor value of 50 ohm seems way too low. I would have thought maybe a 560 ohm. This would produce a current of 21mA @12V which is pretty much a norm for photo diodes or LED's. One resistor on the output is less critical, perhaps a 10K ohm would be fine.

Google Image Result for http://www.buildlog.net/cnc_laser/images/photo_interrupter_circuit.png

Cheers,

Simon

Originally Posted by nearnexus

Thanks Simon.

OK so which of the connection settings shown in the diagrams on the Ebay page for the tachometer are for a Hall sensor?

Rob

OK. First of all, Rob I love your work! Your DC motor conversion looks great!

In terms of the connection:

You will be using the same power supply to drive both the photo interupter and the display? If so then the same ground in common to both and they will both be run from same Vcc. Since the output of the photo interrupt is NOT inverted, ie when the beam is at one of the notches and the beam is transmitted then you will get an output of 12V so I would use the diagram on the far RHS. The tacho has an input impedance of 10K so you should be able to connect the output signal straight to it. You obviously still need the 10K clamping resistor (assuming it's similar to the one in the image I attached) also the signal voltage needs to be between 3 and 30V which it is since you running off 12V

You would be very unlucky indeed if you connected it wrong and you let the magic smoke out!

Good luck

Cheers,

Simon

You recon your a bit rusty, but your still way ahead of me on this stuff

Here's a photo of the back - if that's of any use.

Update: OK thanks for that Simon. I hope I get mirrors and not smoke

I'm still waiting for my batch of KBIC-240 drive controllers to arrive from the USA, so I'm just cruising along on the conversion with lots of time to think about options etc.

The original AC motor was end mounted and the donor is not, so I've had to weld/machine up a cradle to take it. The other option was to pull it apart and make up a new end plate and bearing holder, but that was going to be a lot of work with cooling holes, through bolt locators and possibly key mounts for the main case.

So doing it this way. Looking good so far.

I just hope the 2 HP DC motor has enough power in comparison to the existing 3/4 HP AC unit - which is ideal.

Rob