You don't have a way of measuring the blade speed directly, so you'll have to measure it indirectly and do the necessary maths to get a metres/minute output.
For the measurement part you could detect and count the blade teeth passing over a sensor, or you could find something that rotates - a pulley wheel, or whatever - and count the rotations. Forget trying to count the teeth; for one thing, different blades have different teeth per metre so you'd have to remember to adjust the calibration factor whenever you changed the blade for one of a different pitch. Also, detecting the passage of teeth isn't trivial. So, choose a rotating element - a wheel, a pulley, a shaft - and use that.
There are two easy ways to sense a rotating shaft: optical or magnetic. Both are easy and work well. However, magnetic sensing is more robust and reliable. You need to find somewhere to attach a magnet, and then mount a Hall effect sensor near to it.
You then need to count the pulses from the sensor, convert that into metres/minute, and drive a digital display with the result. A microcontroller will do all of that, and I strongly recommend an Arduino because it's the perfect choice for a beginner.
You said you want it to be powered from the machine, and quite rightly. But not yet. One thing at a time. Develop and debug it running off a battery or plug-top power supply first. Then you can look for a power supply that fits inside the machine and is safe and compliant.
So you have a number of steps, which you should tackle one at a time.
1/ Find a good place to fit the magnet and sensor. Choose somewhere that rotates fairly quickly so the blade speed will be updated quickly.
2/ Select a suitable display module; preferably one with driver electronics so you can drive it directly from the Arduino.
3/ Get your Arduino to time the interval between pulses in milliseconds and output the milliseconds to the digital display. (This is extremely easy to do with the Arduino.) Confirm that the number looks sensible.
4/ Work out how to convert that milliseconds figure into metres/second, and implement in the Arduino.
5/ Work out and implement a suitable power supply arrangement, along with all the physical stuff: mountings, etc.
This is a very high level breakdown; in reality each step involves several sub-steps. We can help flesh out the steps and sub-steps as you proceed. To get help you need to "own" this project and ask for specific help when you get stuck. Nobody here will do the work for you (and I don't believe you would want that anyway).
I think I could probably do this project in half a day, possibly a full day. If you are a complete beginner then we need to be realistic - you are looking at several full days of work. The good thing is, when it's done and working you'll get an amazing sense of achievement.
Finally, the boring bit. If you want this device to be powered off the mains, then you will have to get the input of a qualified electrician to approve and test it for electrical safety, especially as it is in a work environment.
Home
Help
Search
Login
Register
