Now I went and did it. Let the fun begin!

[davidpbest]

But why would you need to tell the tach how many pulses per revolution from the Hall effect sensor.

This tach is designed to allow for any number of hall effect pulses to represent one revolution. On my mill, I have four magnets on the spindle, equally spaced, and at (for example) 60 RPM, the tach is seeing 4 pulses per revolution of the spindle, and the tach needs to know that ther are 4 pulses per RPM to be able to calculate the actual speed of the spindle. On my lathe, I have 8 magnets because I often tap at 8-20 RPM using the Jog function, and want a timely and accurate representation of that speed.

In some applications, 1 pulse per revolution is sufficient accuracy, whereas in other applications 2 or 5 or 10 might be appropriate. Consider this tach on a spindle shaper where the spindle speed never falls below 1,000 RPM. In that situation, one magnet pulse per revolution is sufficient to give a timely and accurate reading. Now consider a situation where this tach is used to accurately measure the speed of a slow turning element (the X-axis lead screw for instance) rotating at 2 RPM (not uncommon). In that scenario, with only 1 magnet, the tach is seeing only 2 pulses per minute and it won't be able to accurately resolve the RPM in less than 1.5 minutes. In that application putting 10 magnets on the spindle at 2 RPM would provide the tach with 20 pulses per revolution, and it could then accurately determine the speed after 3 pulses or in ~5 seconds. Now consider the low slow spindle speed is fluctuating - you'd want even more pulses per revolution in order to have a timely and accurate reading of the RPM at any instant. In all these situations, the tach needs to know the number of magnetic sensor pulses per revolution in order to calculate the true RPM.

Does that help?

 

[Cletus]

Very well presented

 

[Just for fun]

Thanks David,

The pulse per revolution and the RPM does make sense. I'm not sure I understand your switch though. If you have four magnets mounted on the spindle and I can see where that would come in handy. I can follow along on the initial programming but I'm not following along on the switch.

In my mind, if you have four magnets mounted and you change the switch to only read one. The tach would still read all four pulses from the magnets and read four times the actual speed.

Tim

 

[davidpbest]

The pulse per revolution and the RPM does make sense. I'm not sure I understand your switch though.

The switch has several uses. It's a momentary push-switch and a potentiometer combined.

• Push and let go, and it switches the unit from displaying RPM to displaying the calculated SFM (surface feet/minute) or SMM (surface meters per minute).
• When in SFM/SMM mode, a small red LED to the left of the switch illuminates indicating it's displaying SFM/SMM.
• When in RPM mode, turning the dial has no impact.
• When in SFM mode, turning the dial will display and let you set the diameter of the part or tool (0.01" to 99.99" or 0.1-999.9 mm).
• The unit calculates the SFM/SMM based on the entered diameter and the RPM it's sensing. SFM = (RPM x (diameter in hundredths of inches) x 314) / 120000. SMM = (RPM x (diameter in tenths of millimeters) x 314) / 1000000
• Press and hold the momentary switch for 5 seconds or more, and by turning the dial, input the number of pulses (1-90) that represent 1 RPM, and you can switch between metric and imperial readout for the SFM/SMM display function.
• All settings are saved in nonvolatile ROM and faithfully restored on power up.
• This tach can use a variety of sensors in including a hall effect to detect magnets passing by, or other sensors that optically (IR usually) or gear tooth sensors that send pulses.

 

[Just for fun]

Wow David, That impressive and down right cool. Thanks for the information.

Tim

 

[Cletus]

We can expect nothing less from David P Best! .....I really admire his attention to detail and methodology

 

[Just for fun]

I agree 100%, Some of the nicest machines I have seen and some of the coolest technology along with it! Cheers to a Great Job David!

 

[davidpbest]

We can expect nothing less from David P Best! .....I really admire his attention to detail and methodology

Thanks guys. At this stage in my life, my primary motivation is helping others, so I hope that's coming through. With regard to the tach I described, I did not design the beast, I just built it from published information. It was designed by Henry Arnold, and for a period, he was selling a DIY kit (similar concept to Clough42's ELS) that included the PCB, a custom ASIC chip, and a bunch of discrete components (resistors/caps/etc.) along with detailed instructions. The hand soldering was a challenge given the size. Henry stopped selling the kits quite a while ago, but has left breadcrumbs on Thingiverse here. I used to build HeathKits as a kid, so tackling this was right up my alley. If someone wants to build one of these, DM me - I think I have the parts on hand for one unit. When finished, this is what the thing looks like, and you need to figure out how to mount it. The display/potentiometer is on the back side.

 

[Cletus]

Ahhh, HEATHKIT! ...So many memories. I still have Heathkit stuff in my lab which I built 49 years ago, never been opened since, still functional and still holding decent calibration. Don't really use them anymore as they've been replaced by more modern instrumentation, but nostalgic bits of my entry into a wonderful, successful and fulfilling career!
......Apologies for veering off topic guys, could not resist!

 

[Just for fun]

It sounds like Monday will be the day. I'm pretty excited as one can expect but there is some drama to go along with it. The county has put weight restrictions on the road I live on. I talked with the trucking company today, the plan is to meet with the trucking company at the local equipment rental location downtown and transfer the equipment from there truck to my flatbed car trailer. I'm not excited about that venture, but I'm sure it will work out. Then, once I get it home, I will have to unload them with my Kubota tractor and get them in the shop. The good thing it is only a two- and half-mile road trip.

Tim