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Optical Tachometer

Started by Jason_WI, March 27, 2003, 06:37:30 PM

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Jason_WI

I have built an optical tachometer that uses reflective tape to count pulses off of anything that rotates. Right now I have a prototype built on a PIC proto board. I want to install this on my bandmill to monitor the RPM of the crankshaft and also on the band wheel itself to monitor surface feet per minute. I have a few other uses for this also such as my lathe spindle rpm and my dad's combine engine speed and cylinder rpm.

I can etch a few extra boards if any of you FF members are interested in a optical tach. I am going to estimate cost at around ~$30. Basically made from surplus electronics.

It could be powered off of a 9 V battery, DC wall wart, or 12 V auto system.







The sensors are cheap at $.75 each. Long wires can be added for remote monitoring. I am planning to use a LCD display. I know that they tend to be sluggish in cold weather but they are cheap and easy to interface to. 7 segment LED displays could be used but the code is more difficult and the PIC's that I have on hand would not have enough I/O lines to drive them.

Jason

Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Fla._Deadheader

How would it be hooked up? Is the readout waterproof or do ya have to be sure it's under cover? I am using an old dwell tach and today I had to shut down to take it out of the rain. I know NOTHING about electronics.. ::)
All truth passes through three stages:
   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

Tom

Smart fellow, Jason.

You know you could be handy fixing the speed control Boards on the woodmizer sawmills.  They used to repair them but got out of the business and only sell new ones now. If you felt comfortable doing that, there might be a little business there by listing in the Forestry Forum "services" area and by letting Wood Mizer know that you are available to perform the service if they would like to recommend you.  You would have to get hold of the board and study it and then let the word get out on the forums.  That might be the beginning of something bigger.  Setworks are becoming the thing and all they are are little computers that sawmill owners don't know how to fix. "Course the logistics of learning everybodies systems might be difficult.   Hmmmmm  some of these small, new manufacturers might even need someone to design their setworks for them. :)

biziedizie

Jason that would be a pretty interesting thing to have on the mill. It would be cool to see the rpm as the blade goes the length of the log. How would it handle vibration?

    Steve

Jason_WI

With a cheap project box from radio shack and some RTV it would be waterproof. The circuit board can be conformal coated for corrosive conditions (salt air). The optical sensors are waterproof as they are epoxy sealed. I suppose if the screw that held them in place was overtighned and the case was cracked, water could creap in and cause problem.

Hookup is simple. Attach black wire to neg(-) battery post. Attach red wire to pos(+) battery post. Voltage can be anywhere from 7.5 to 20 volts DC.

Next fabricate some sort of bracket to mount the optical sensor so that the distance can be adjusted from 1/8" to 3/8" from the rotating shaft or side of a pulley.

Attach reflective tape (aluminum/chrome tape) in two locations 180 degrees apart on the shaft or pulley. If the pulley or shaft is painted flat black that would be optimal.

With 2 counts per revolution and each sensor being monitored for 1/2 second it will have a resolution of 60 RPM which should be good enough. 4 counts per rev would get 15 RPM resolution which would be better. I can make it selectable with jumpers on the board from 1 to 4 counts per rev.

Adjust the gain by turning a pot to get a reading. This is the tricky part as the distance from the reflective tape to the sensor can vary that's why you need to tweak a pot to get the sensor in it's sweet spot.

For displaying Surface feet per minute, a few peramaters would need to be programmed into the PIC when I program them.

Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Jason_WI

Steve,

The picture is just a prototype I have built. It probably wouldn't last very long on the mill with all the dust and vibration.

I need to layout a circuit board and will use all surface mount parts that have a low profile so there ability to withstand shock and vibration will be ten fold over the prototype you see in the picture.

I have proved the circuit on the bench an now I need to capture this into my final design and install it on the mill.

I may use the proto for some initial testing on my mill but once I an confidante the topology of the circuit is ok then I will make a final, robust tach that should last for years.

Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

biziedizie

That sound like you have a good plan there. Keep us posted it would be cool to hear the results of how it works.


    Steve

leweee

Jason   could a board be designed to enclude a digital hourmeter for manual mills without all the bells & whistles ???Leweee
just another beaver with a chainsaw &  it's never so bad that it couldn't get worse.

ElectricAl

Jason,

What I need is "Auto up".  

Your last cut is around 4" but the opening cut on the next log  is 20", so as all WM owners know it's break time. Waiting for the head to raise is boring. If the log is real big a guy's got enough time to pound down a can of pop and a snickers bar. :D

What I want is to push a momentary contact button and have the head go up to 20" and stop. ;)
This way I can go do some other task.

What do you think?


ElectricAL
Linda and I custom saw NHLA Grade Lumber, do retail sales, and provide Kiln Services full time.

Bibbyman

E-Al.  Have I got a deal for you!   8)

We just got our new board for our Accuset and it has four "reference" sets.  They took the obscure function button on the far left of the board and made it a "reference mode".  Hit this button and then the up/down lever the head will go to one of the four set locations.  The set locations set from the factory are 1",12", 24" and 34-1/2". (red buttons marked 1,2,3,4 on right side)  They can be re-programmed.  

So,  when you want to go to 24" for the next log - hit the "reference" button and then the up/down switch and there it goes. (Provided the 24" set is the last one chose.  If not, you'll have to hit the button it's programmed for - in our case button #2).

Now,  our Super has a potential head speed about twice that of a standard mill - due to its larger motors.  But after using it over a year now, even it appears to go too slow.  But with the reference mode,  you can now turn your attention to loading or turning a log, etc.



BTW,  the new Accuset logic is much easier and quicker to program.
Wood-Mizer LT40HDE25 Super 25hp 3ph with Command Control and Accuset.
Sawing since '94

Rick Schmalzried

Jason,
Is your $30 estimate for the circuit board only, or for a board and the necessary parts?
Now for the tech questions.... ???
What microprocessor are you using?
How are you handling the analog interface from the optical sensor?
I started to do this about 10 years ago and finally decided it wasn't worth my time.  I was going to have to put about 100 hours into it and I could buy a commercial unit for $200.  Besides I was doing that type of work all day for a job and it wasn't relaxing.  That is why I started doing woodworking instead.  Now I am not in the electronics as much and I wouldn't mind breadboarding a system if I had a schematic and the program.

Finally, what would it take to modify this for a temperature sensor?  Do you have any analog input capabilities?  Do you have any serial output capability?  

Boy...Too many questions, too little time :D

--Rick
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Norm

That sounds awfully handy, what was the cost of the new board for your accuset Bibby?

Bibbyman

Ours was replaced under warrantee.  You may check with WM service.
Wood-Mizer LT40HDE25 Super 25hp 3ph with Command Control and Accuset.
Sawing since '94

Jason_WI

Rick,

The microcontroller on the prototype is a PIC16C73 from Microchip (www.microchip.com). I am planing on using a PIC16C711 for the final design. I have a boatload of these PIC's.

The optical sensor output is converted to a square wave and fed directly into a pin on the micro. The pulses are then counted for 500 ms and then converted to RPM or SFPM.

Yes, the micro has analog input capability and could potentially monitor a temp sensor. There are digital temp sensors available now but that depends on what range of temperatures that you want to monitor. Serial output is available also with a MAX232 added to the design.

I have 3 hours total in this design so far. That includes writing the code and building the circuit you see in the picture.

Here is the code that makes it work:

'Programmer: Jason Birnschein
'Date: 3/27/03

DEFINE OSC 4

'----------Define LCD registers and bits-------------
DEFINE  LCD_DREG        PORTB
DEFINE  LCD_DBIT        4
DEFINE  LCD_RSREG       PORTB
DEFINE  LCD_RSBIT       1
DEFINE  LCD_EREG        PORTB
DEFINE  LCD_EBIT        0



'---------------VAR's--------------------------------
WORD         ENG            VAR

WORD          BAND                       VAR      
      
            
            
'------------------Main program----------------------

        Pause 100       ' Wait for LCD to start up


Splash:

        LCDOut $fe, 1   ' Clear screen
        Pause 500       ' Wait .5 second

        LCDOut $FE, $80, "  Poor Man's"              
        LCDOut $FE, $C0, "  Tachometer"  
        Pause 2000       ' Wait
        LCDOut $FE, 1
        LCDOut $FE, $80, "  03/27/2003"              

        LCDOut $FE, $C0, "Jason Birnschein"  
        Pause 2000       ' Wait

        LCDOut $fe, 1   ' Clear screen
        Pause 200      ' Wait .2 second
        
Main:
        
        Count PORTB.2,500,ENG
        Count PORTB.3,500,BAND
        
        ENG = ENG * 60       'this assumes 2 counts per rev
        
        
        LCDOut $FE, $80, "RPM = ", DEC ENG DIG 4, DEC ENG DIG 3, DEC ENG DIG 2, DEC ENG DIG 1, DEC ENG DIG 0
             
        LCDOut $FE, $C0, "SFPM = ", DEC BAND DIG 3, DEC BAND DIG 2, DEC BAND DIG 1, DEC BAND DIG 0
        
        GoTo Main  

END


As you can see it is pretty simple. I use PicBasic Pro from MELabs for the compliler. There are free C complilers out there but since I am not fluent in C I have decided to stick with what I know. I have been programing in basic since ~1986 when I was in 6th grade on an Apple II. ;D

Jason

Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Rick Schmalzried

Wow, the short time  you have invested shows how much processors have changed and gotten easier.  I was working with a Motorolla 68HC11 and was programming in assembly.  I had to write more code than your entire application just to get the device to work in a timed loop.

I assume the PIC controller has built in flash ROM, etc.  How could I program it w/o having an evaluation kit?  I guess I need to check out microchip again.  It has been about 4 years since I looked at them.

--Rick
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crosscut

 :D wonder if it would hook up to my ears cause my heads spinning after this topic

Jason_WI

My cheap source for reflective optical sensors has dried up :'(

I bought 4 sensors a few weeks ago from www.allelectronics.com and now they are sold out... Guess you can't rely on surplus ;D

But there are other companies that make these. Fairchild semiconductor makes one that is similar.

I am going to install the sensors I have on my mill today and see how they perform. I am going to boost the counts per rev to 8 to get a decent resolution.

Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

wiam

Is this sort of like what you are building?

  www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=41727  

William

sawwood


 Jason how and where would you hook the sensor to the lathe
 spindle? I would like one if  i can put the led unit in a box and
 mount it on the lathe. Let me know by e-mail to
 allengillett@comcast.net
Norwood M4 manual mill, Solar Kiln, Woodmaster
18" planer/molder

Jason_WI

I have tested my prototype on the mill and everything looks good. Forgot my camera so no pics. I think I am going to use 4 red or green 7 segment displays for the display. The LCD I was using was pretty sluggish at 30 F and the viewing angle wasn't the best. I'm thinking some .5" high displays would work nicely. It may push the cost up a little but at least it will be readable at a distance.


William,

The horrible freight one is going to cost more that the one I am going to make. Besides how would be able to mount that hand held unit to the mill and still be able to look at the LCD output?

sawwood,

I have to take the side cover off of my Rockwell 14x40 yet so I'm not quite sure yet on that. One idea is to use an encoder disk with holes drilled in it and somehow mount it to the spindle. Usually there is a gear on the spindle that drives the quick change gearbox. The encoder disk could be sandwiched to the gear on the spindle. The tach on the spindle will be nice as the Rockwell has a variable speed Reeves drive and I can now only guess at what RPM the spindle is.
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

sawwood


  Jason my lathe is a 12 X 32 older Rockwell/Delta. There is
 a index ring on the back that is held on by a large round
 nut. May be the encoder disc could be put between the nut
 and ring?  Will try to take some photos so you will have a
 better look at what i have.

 Sawwood
Norwood M4 manual mill, Solar Kiln, Woodmaster
18" planer/molder

Jason_WI

I haven't forgot about this project. I was waiting for some free samples of a LED display driver IC. It will make life easier when I write the code for the processor. Using 4 red LED displays will make it alot easier to see than using the LCD.

I will hopefully have time this week to hook it all up and put it in a little project box.

I have found a replacement sensor that will work with the currrent design that costs ~$1.50.

I am planning on etching 10 boards to start with. Once I have the final design I can calculate a final cost for those interested.

Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

Fla._Deadheader

Jason. Put me on your list.
All truth passes through three stages:
   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

Jason_WI

Dusted off this post...... Had to find my prototype tach under a pile of unfinished projects :-/

Well I have decided to go with an LCD after all. It will keep the cost down and I have found one with a backlight for 8 bux. It is a 2x12 LCD with backlight.

Is there still interest in this??

The plan is to use the 12 volt system on the piece of equipment you want to mount this on. An AC adapter can be used if mounted on a lathe.

I will etch boards cause I'm using all surfacemount parts. The board will be fitted in an enclosure with the LCD.


Jason
Norwood LM2000, 20HP Honda, 3 bed extentions. Norwood Edgemate edger. Gehl 4835SXT

smwwoody

sounds great I would like one let me know wwhat the cost is.

Will a third party post dated out of state check due :D ;D
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