PIC based DRO

[BillTodd]

Continued from Welcome thread

Look like you haave been busy. The engraver looks great.

Thanks

I would be interested in how you used the PICs for your DRO`s. Did you design them yourself? I wonder if they could work using encoders ? Mario

The DRO (still work in progress) uses one 12F675 per channel to read the digital scale. The outputs of four PIC are multiplexed into one serial port of a PC. The PC runs a VB5 application that displays the readings (see attached).

The layout of the main form is designed to match my homebrew PC's touchswitches that are arranged down the left and right sides of the display

I spent sometime getting every thing to talk to each other neatly, so for instance, you can plug an extra vernier/scale into the adapter block and it just pops up on the screen.

As to using the PICs with quadrature encoder, I'm sure the little 8 pinners I've used lack the necessary hardware (you'd need a couple of fast counters to ensure no pulses were lost). The ones to use would be the dsPIC devices like the 30F4012 (?) which have the quadrature hardware inside.

[mc_n_g]

Could you post more metails on the project. I have been playing in various pics of the past year and would like to get a little more advanced in reading other pulses.

[BillTodd]

Originally Posted by mc_n_g Could you post more metails on the project. I have been playing in various pics of the past year and would like to get a little more advanced in reading other pulses.

What pulses are you trying to read?

[mc_n_g]

I am trying to do a better job in understanding teh analog and digital side of the processing. I have played with temp sensors and other simple items for input. I have not worked with any encoders at all. This is where I am lacking examples and expereience.

[BillTodd]

I'm not actually reading encoders. I'm decoding the digital data outputs of those cheap Chinese digital calipers (see :examples here). To keep my circuit simple, I'm using the PICs onboard comparitor and reference to convert the low level (~1.5v) signal to one that the PIC can read.

This circuit is of a single device reader powered by the serial port.



The LEDs (D1,2,3) limit the voltage to about 1.2v when the PIC drives the scale's inputs.

[Marzan]

As to using the PICs with quadrature encoder, I'm sure the little 8 pinners I've used lack the necessary hardware (you'd need a couple of fast counters to ensure no pulses were lost). The ones to use would be the dsPIC devices like the 30F4012 (?) which have the quadrature hardware inside.[/QUOTE]


Hi Bill. It all looks impressive. You have certainly done a good job. I wish I had your talents. Unfortunately I am just a Trial and error learner at both electronics and Cnc`ing If i had one wish it would be that there was a way to verify my steppers with an encoder in Mach 3. A task too difficult for me with my limited experience.

Marz

[BillTodd]

If i had one wish it would be that there was a way to verify my steppers with an encoder

The usual method is to mark the motor's starting position accurately, then run a torture test (i.e. a test that runs the motor at various speeds back and forth until finally return ing to the start point), then check the motor has returned to the start postition correctly.

[Marzan]

The usual method is to mark the motor's starting position accurately, then run a torture test (i.e. a test that runs the motor at various speeds back and forth until finally return ing to the start point), then check the motor has returned to the start postition correctly.

Yer Bill. I have done all that. I set up a dial indicator on both axis and then ran a g code program with rapid moves for a 1/2 hr. I tuned the motors for 10% under the max revs before it misses pulses. Its just sometimes if I push the toolbit too hard it misses a few steps. I know thats my fault, but it would be nice if it could correct itself. If only I had the money to run servos....


Marz

[BillTodd]

but it would be nice if it could correct itself.

I see. Can mach3 do that, if it has encoder/count inputs?

What sort of input does Mach3 need?

[Marzan]

Originally Posted by BillTodd I see. Can mach3 do that, if it has encoder/count inputs? What sort of input does Mach3 need?

I`m not really sure.I was thinking along the lines of another pic or such countin pulses and comparing the result with an encoder (sort of like a virtual closed loop system) and if it misses steps using one of the inputs to signal a positioning error

Marz

[Robin Hewitt]

I'm brewing up much the same but with a home made computer board reading scales and stepping motors.

The step timer interrupt compares "where I am" with "where I want to be" and steps accordingly.

The "where I am" can change at any moment should a report be received from any of the 3 scale interrupts. (I read them with hardware because any lag will only serve to confuse it).

At the end of an x,y,z stepping sequence it works out the error on all 3 axes. Should any be outside tolerance it doesn't update the "where I want to be" to a new position. This means I get remedial steps to put it back on course.

Questions are, wil it do more remedial steps than moving steps, and, how tight can I put the tolerance

I only have to mount the scales and I can find out

[BillTodd]

Originally Posted by Robin Hewitt I'm brewing up much the same but with a home made computer board reading scales and stepping motors. The step timer interrupt compares "where I am" with "where I want to be" and steps accordingly. The "where I am" can change at any moment should a report be received from any of the 3 scale interrupts. (I read them with hardware because any lag will only serve to confuse it). At the end of an x,y,z stepping sequence it works out the error on all 3 axes. Should any be outside tolerance it doesn't update the "where I want to be" to a new position. This means I get remedial steps to put it back on course. Questions are, wil it do more remedial steps than moving steps, and, how tight can I put the tolerance I only have to mount the scales and I can find out

Interesting idea Although,the missed steps may not be able to be corrected until the cause has been removed.

i.e. if it drops steps because of excess speed v load, will there be time to correct them before the next motion without increasing the frequency of the pulses thus exacerbating the speed v load problem?

(Well worth trying though )