diy tach

[swarfmacdaddy]

Does anyone know of a simple diy circuit for a tachometer with enough range for a router? ( 30,000 rpm) Any thoughts would be greatly appreciated.

[ViperTX]

And you are trying to accomplish what??

[swarfmacdaddy]

get an accurate spindle reading when using a router speed control

[borrisl]

You could try www.cnc4pc.com. They have an inexpensive tach that can be mounted on the bottom of the router motor. They require a small disc with a hole in them. Should be easy to mount to the router output shaft. I haven't tested it yet, but I have the same unit and trying to do the same thing.

[Zippi]

I don't have a schematic, but being that this is the Electronics forum, I can start you in the right direction...

Start with a Microchip PIC, something like a 16F84. Use an opto tx / rx to sense either a slot in a disc (1 slot=1 RPM), or a reflective spot on a shaft. You could even use the opto parts from a computer's mouse, for example (would be fine for the RPM's you're talking about). Time the pulse cycles, that'd give you RPM. Then, you can drive an LCD with the PIC, even drive an LED display (there're MAX chips that drives 7-segment displays, it's a pricey chip, can't remember the number, but it's easy to use). You could also use the PIC to send serial RPM's back to some controller.

Once you've got a PIC telling you RPM's, it isn't a far step to have it control spindle RPM itself, such as setting speed from a PC. Get a digital potentiometer, and wire it in place of your spindle control's potentiometer. Hook it up to the PIC, control the PIC with the PC. Programatic spindle control. It would even be possible to have the PIC do load compensation (though, reaction time will play a part), controlling spindle power based on desired RPM and load.

Just to get RPM, even easier yet, hook your printer port up to the opto sensor, write a program in something like "QuickBasic" (if you can find it), even in assembly language if you're REALLY good, under DOS (not a dos session in windows), poll the printer port, time the pulses, display RPM on the screen. Easy to do if you have spare PC's floating around (who doesn't? LOL!).

You could even write a windows application to display RPM using the PIC feeding serial data to the PC. Labview and all! LOL!

There are lots of ways to do this!!!

I'll probably end up building a PC control for my spindle eventually, but it's not a priority right now....

[swarfmacdaddy]

Zippi,
Thanks for the info! Looks like a cool project for winter. I have seen tachos on ebay for $35 but not quite the same as making it yourself.
REAL MEN DONT BUY TOYS THEY MAKE EM!

[NC Cams]

Look at Red Lion for counters/meter movement - they also have inductive pickups that, when matched with counters and a target can be used to make up tachometers.

An inductive pickup or a "chopper wheei" triggered LED would be what I'd look at for triggering. If you can propely shield and fasten it, however, a gear can be mounted to the shaft and the inductive p/u will sense the gear teeth - the Red Lion counter will convert to RPM.

You can also use the LM2907/LM2917 IC and make a tach - this is an F-V converter from National. There should be circuit diagrams in the application note.

Same triggers as mentioned above could be used to trigger it.

IF you do decide to use the F-V method, make sure your count frequency is within the response curve of the IC and surrounding hardware....