Acorn to DMM DYN4 - Differential Line Driver Board

[kentonsj]

In light of recent topics regard noise and lost steps, I started thinking last night about making a custom circuit board that would plug into H2 and H3 for the Step and Direction signals and use a differential line driver to enable the differential connections to the DYN4. I would like to arrange my custom board with DB9 connectors that I could use to make a custom cable from DB9 to DB25 for the DYN4. I came across a TI Dual High-Speed Differential Line Driver IC last night, after some research. I'm thinking that I could use this IC directly from the single ended outputs on the Acorn, using a pull-up resistor to 24V. The outputs could connect directly to pins 11/23 and 10/22 on the DYN4. Does anyone have any thoughts on if this will or won't work? I like the idea of how clean this could look in the panel. I found some header pins that should mate directly to the acorn header.

Here's a preliminary sketch for one axis of the step and direction signals.

Differential Line Driver TI ua9638.pdf

(407.69 KiB) Downloaded 173 times

[Gary Campbell]

Am I correct in assuming you are developing a product that replicates the output from the DB25 header?

[kentonsj]

I was trying to find a way to use the DB25 header, but I don't see any way to enable the DYN4 drives without using one of the 4 precious outputs. This also would eliminate the single ended step and direction signals and allow for differential step and direction signals. My board would have four DB9 connectors, each connector would carry: Step and Direction, +24V, Com, Alarm, Enable and Brake signal from the DYN4 in case you have a holding brake (As I do on my Z axis). So in short, this isn't a replication of the DB25 header

[cncman172]

Gary,
The Acorn DB25 connector does NOT provide differential output signals. Those are single ended output signals. He wants to build a product that takes the singled ended signals Step and Direction and makes them Step, Step/, Dir, Dir/ which is want many commercial drivers accept.

Here is a picture of a similar board I made to accomplish the same task. I use Panasonic amplifiers and they work much better using differential step and direction inputs, they can take faster input streams, and they are much more noise immune.

Russ

[eng199]

In light of recent topics regard noise and lost steps, I started thinking last night about making a custom circuit board that would plug into H2 and H3 for the Step and Direction signals and use a differential line driver to enable the differential connections to the DYN4.

Pulling the UA9638C inputs up to 24V is a very bad idea. The chip's input voltage is 7V absolute maximum.

You would be better off getting step and direction from the DB25 to avoid extra delay from the open collectors and pull ups.

I would use a quad driver such as the AM26C31.

[cncman172]

eng199,
You are correct, I actually use the AM26C31 part, and actually pull the signals directly from the DB25, since they are TTL and have build in pull up resistors.

Russ

[cncman172]

eng199,
You could pull up the outputs to 5V, since those Acorn screw terminal outputs are open collector.

Russ

[kentonsj]

If I use the DB25 port, which sounds like best idea for the line drivers, can I still use the screw header connections for my drive enable signals? I could use one of the 4 outputs on the DB25 and enable all the drives at the same time if the enable screw connections aren't enabled while using the DB25 connection.

[kentonsj]

Gary,
The Acorn DB25 connector does NOT provide differential output signals. Those are single ended output signals. He wants to build a product that takes the singled ended signals Step and Direction and makes them Step, Step/, Dir, Dir/ which is want many commercial drivers accept.


IMG_2379.JPG

Here is a picture of a similar board I made to accomplish the same task. I use Panasonic amplifiers and they work much better using differential step and direction inputs, they can take faster input streams, and they are much more noise immune.

Russ

cncman172,
Do you have another picture of your setup that shows the db25 connector on the acorn as well. To me it does look like you are still using the enable terminals on H2 and H3.

[cncman172]

YES,
You are 100% correct, I am using the Enable signals from the Screw terminals since they are not available on the DB25.

Russ