modify MPG to differential encoder

[Karl_T]

For my next project I'll be making a Jog Pendant with a very long cable.

I'll have a handwheel, or MPG, on this pendant. All the ones I've used are just a single end encoder with A+ and B+ channels. I just went through painful episode where the trouble was traced to single end encoder on my lathe X axis. Don't want to take a chance on this issue here.

Anyway, I noted going from single ended to differential on USdigital encoders involved adding a samll IC board right at the encoder. Cand the same thing be done for a MPG? How?

Karl

[TOTALLYRC]

Originally Posted by Karl_T For my next project I'll be making a Jog Pendant with a very long cable. I'll have a handwheel, or MPG, on this pendant. All the ones I've used are just a single end encoder with A+ and B+ channels. I just went through painful episode where the trouble was traced to single end encoder on my lathe X axis. Don't want to take a chance on this issue here. Anyway, I noted going from single ended to differential on USdigital encoders involved adding a samll IC board right at the encoder. Cand the same thing be done for a MPG? How? Karl

Since an mpg is just basically an encoder whith a hand wheel attached, it is done the same way. You will also need a differential to single ended converter at the other end to make full use of the differential signals benifits.

[Al_The_Man]

26LS31 Differential line driver.
Al.

[Karl_T]

Would you double check my wiring?

http://www.national.com/ds/DS/DS26LS31C.pdf

pin16 +5volt
pin8 ground
pin1 mpg input A
pin7 mpg input B

pin2 A+
pin3 A-
pin5 B+
pin6 B-

The last four pins go on to a Galil 1900 ICM

Karl

P.S. edit, I must need to power the enable pins?

[TOTALLYRC]

Looks good to me Carl.
Since you are going to a differential input device, you will not need the decoder chip at the galil end.

Depending on the encoder that you are using, you may need a capcitor or 2 right at the chip to smooth out the power going to the encoder. I have 2 different sizes on mine, I can find out exactly what they are if you need me to.

As the encoder switches on and off it can cause large enough swings in the power going to the chip to cause it to go crazy, the caps will stop this.

Mike

[Karl_T]

Yes, would you let me know what size caps, please?

Did you pick up my edit? asking about the enable pins?

Karl

[TOTALLYRC]

Originally Posted by Karl_T Yes, would you let me know what size caps, please? Did you pick up my edit? asking about the enable pins? Karl

Sorry Karl, missed the edit. I don't believe that you need to use the enable pin but you may need to depending on wether it enables or disables the chip when it is not connected
I will have to go outside and look to see what I used and verify the enable pin usage.

Mike

[Al_The_Man]

You should tie pin 4 high (5v) and pin 12 (com).
~10µf should suffice.
See post #5 here http://www.cnczone.com/forums/showthread.php?t=8694
Al.