Not a dumb question, Iggy. Quadrature outputs occupy two bits. So, you have enough inputs on the parallel port to handle up to four encoders.
If the i/o chip on the parallel is the right sort (old 8255-ish behavior, perpetuated in more modern on-board integrated I/Os), you can set the chip to interrupt on any input change. That'll avoid your having to poll the chip constantly; you can just update the position information in an interrupt handler when a bit twiddles.
LLoyd
Looks like some companies sell breakout boards that do a lot of useful things, one of which is proper buffering/interrupt handling (in reference to Lloyd's suggestion also).
Thanks a lot. I think that once I understand the role of various components, it is a relatively straightforward task.
i
OK, thanks Lloyd. Check this out:
Part 7544 and 7525 should cover the needs for reading information from encoders and will also permit some forms of machine control. I will give them a call when I get some time.
i====================================================================== The MOTENC-Lite PCI board is designed for PC based real-time systems controlling machines that require precision motion control. These include, CNC machines, Routers, Pick and Place machines, Robots and so on. The board has all the necessary components to implement a precision digital feed back control system. Analog outputs from the board drive the Motor Amplifiers using industry standard ±10V interface. The position feedback is generated by the quadrature encoder counters using 32-bit resolution. Utilizing the full 32-bit PCI bus, the board allows reading the 32-bit counter in just one read cycle. The Analog output settling time is just under 5 micro-sec and the CPU read-write cycle times are within 500 nano-sec. This allows the PID feedback loop update rate of 20KHz or more. The board has digital I/O to connect home, limit, and other switches and relays to implement a complete control system.
The MOTENC-Lite board is supported on EMC/EMC2 (Enhanced Machine Control) software. EMC is a software system for computer control of machine tools such as milling machines. More info available at
Product Highlights:
*Eight Channels Analog Outputs, Range ±10V, 13-Bit Resolution *
Eight Channels Analog Inputs, Range ±5Volts, 14-bit Resolution *
Four Differential Quadrature Encoder Inputs. 32-Bit Resolution *
2Mhz Max encoder frequency. Encoder resolution is multiplied by 4 in hardware * 48 Digital I/O (32 Inputs & 16 Outputs) in two 50-pin headers. Opto-22 compatible * 10 additional Digital I/O (6 Input,4 Output) on two SIP headers. *Programmable Timer Interrupts *
Watch Dog Timer *
Optional Hardware ESTOPs Input Signals (Jumpers on board to override if not needed) *
Hardware Board ID for multiple board applications
No I haven't tried it, I was just basing it on the information I read in the EMC2 details and the examples on the EMC2 live CD. While it does mention an upper limit to what it can cope with frequency wise with the software quadrature decoder in the RT core, I can't recall it. One would have to make sure that the system they were trying to build didn't exceed that limit or use a hardware solution instead if the higher rate was required.
Funny, I have a 3Ghz P4 system with four USB ports and two serial (RS232) ports. Open thy eyes, RS232 'aint going anywhere for a good while.
Pete C.
that is certainly on the right track. But the kit is $189
Maybe I just need to buy the scales and read them directly until I get tired of that and pony up for the display.
CDN$
US$
Numbers look even worse if you compare functionality.
Nick
Here's a couple of links I had bookmarked that may be of interest to you. I had seen some other stuff about interfacing a PC to digital scales, may have been a link from the Mach CNC software website.
IIRC the Newall uses the connection to upgrade the software of the DRO.
Can't think of anything that a DRO might be able to do, that should not have already been programmed in, so it seems a little redundant.
The Newall website says " This is designed for programming of the unit during manufacture, CSS communications and diagnostic purposes. It also fulfills the requirement to log positional data for quality purposes."
I have no idea how they figure that logging positional data will help out the quality, other than proving that the operator was not asleep, but that's about the only use it seems to have that does not involve an even heavier investment in infrastructure to make use of it.
Seems a no brainer to me. It amounts to money wasted.
Cheers Trevor Jones
Isn't that pretty much what the likes of the YADRO do? (Yet Another DRO)
OK, 189.00 CAD =177.118 USD
A little better
Agreed, but it's functionality I don't need at the moment. Older Laptop or PC has some maintenance requirements Time spent soldering components to board.
Not a slam dunk, but not out of the question.
Well, you asked for an interface to the PC. The one from littlemachineshop certainly is cheap, but doesn't have that interface. Again, compare the functionality with any DRO and you'll see that you get what you pay for. :-)
An other nice DRO (but without serial output) is the Shumatch ().
The yadro is the only one in the low-budget range that supports 4 axes. Handy if you want to have a scale on the mill's quill. It does the math for you.
If you are using the el-cheapos, you'll soon discover what they are missing. On a mill that is finding the center between two points, bolt circles (no more RT for that), point sequences, tool geometry correction (add/subtract radius of mill automatically) etc. That's what a DRO is for, not just for displaying unprocessed numbers. On a lathe, that is adding the Z-axes and handling a swiveled compound (top slide).
End of shameless plug. :-)
You'll discover that you spend much more time to mount the scales to your mill/lathe.
Nick
Duly noted. My immediate project requires a DRO, but doesn't require any of those additional functions. Call me myopic ;)
Granted. I think at this point I'm looking for a $400 kit. I just know they are out there.
But I can probably do what I need to do with 3 scales and reading the digits right off each scale. Sounds clumsy, but I don't see why it wouldn't work. And I can add the display unit later.
i also fail to see the value with this
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