DIY RPM gauge with Hall or Reed sensor

[Fred Bronk]

Hi Guys,

Anyway I have a couple Mills and Lathes (Wabeco-Speedway-Emco) and would like to make RPM sensors for them.

My idea is to use a Hall or Reed sensor to replace the optical sensor on the tachs we use. Pretty simple if it works.

I understand the Hall would need a power source and the Reed would not.

Basically all 3 should work the same, right. They just complete the circut.

Can someone help with links or how to wire these up? I think I can hande it when I know how to do it :D

FB

[Bearded Flyer]

Just a thought but if you already have an optical tach then why not just stick a thin piece of reflective tape on the chuck and sense off that? The tach that I have (acquired during a clear out at work) has reflective strips supplied in the case for this purpose. It will not cost much to try it out. If you need to get the tach further away from the machines then fibre optics could be the way forward.

Just some musings late at night :)

Richard

[Dan Baldwin]

I would think that a hall effect sensor would work fine for your purpose, although I couldn't tell you how to hook it up to your optical tach because I have no idea what type of sensor they are using, or how it's wired. A hall effect sensor is simple. It has 3 leads; ground, VCC (probably anywhere from 3-20 volts), and output.

I don't think a reed sensor would be a good choice. It's actually a mechanical reed switch, so it has all the problems inherent with mechanical switches; it will probably bounce on make, can handle a finite number of cycles, it may not be able to handle high spindle speeds, etc.

Dan

[Fred Bronk]

I thought about that but having to wire a light source up in an oil filled, greasy closed area may not work.

With a magnet or metal surface it would be no issue.

THX

[Dan Baldwin]

here's (http://www.mouser.com/catalog/629/295.pdf) a page from the mouser catalog showing some hall effect sensors and pinouts.

Dan

[podavis]

'Allegro' has 5 volt hall sensors. other companies too, that could drive a transistor. The transistor would drive an LED that is pointed into the light receiver on the Tach. No changes to the tach!

[Fred Bronk]

I am taking the Tach apart to place the readout in a housing to match the machines.

If the Hall sensor will work on the same 3v as the tach, I can use one power source for both. Of course this can be adjusted via a resistor if needed.

So if the Hall sensor will give me the same signal as the photocell, it would work fine.

If I could do it with just the photocell and have it work of an LED and reflective tape, that would great, but only in a non splash-lubed area.

The last idea maybe the best if the Hall sensor proves to need to many parts, etc I would just have to find another spot to put the sensor.

FB

[ZAGNUT]

make sure the hall sensor you chose is non-latching or whatever it's called...you want the signal to go high when the magnet is under it and then return to low when the magnet leaves. many will go high and stay there until they see the opposite pole of the same or another magnet.

i think most are rated for a minimum of 4.5 volts but there are 2.7 volt models to be found if you look hard enough.


dave

[Fred Bronk]

Sounds good Dave, that is the kind of info I was looking for.

The Hall sensor I think is the way to go as it is a set and forget setup.

So 3v for Hall and the Tach, a couple magnets to simulate a prop should work.

THX

[ZAGNUT]

with the tach on my TX i can simply wire the output of a hall sensor straight to the tach input pin of the microcontroller and it works like a charm....although i'm betting a resistor in series might be a good thing.

all the circuitry found in the tach module itself is just there to amplify the weak signal from the phototransistor and is not needed with a hall sensor.

don't know what tach you plan to use but it would probably work the same.

the sensor i used was a panasonic DN6852 and the min. voltage rating is 3.6....out of stock at digikey but dig around in their catalog and you'll find something that works with a lower voltage.

or if your tach has a simple linear regulator you could probably double the battery voltage and run power straight from there to the sensor, the tach itself probably draws so little current that the regulator wouldn't care.


dave

[Fred Bronk]

I have the cheapo great planes tach. If I can just do that it would be great. No trans just 3v to the sensor off the tach itself :D

FB