Acorn to DMM DYN4 - Differential Line Driver Board

[eng199]

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

I'm not sure if you're talking about the ACORN output or AM26C31 input.
There are only pull up resistors on older ACORN revisions. If your ACORN is 170918 or newer, it has push-pull drivers for the DB25.
The AM26C31 has TTL compatible input levels, but no pull up resistors.

Just realized that I may have needed pullup resistors because my Acorn is a Rev 3. Did I miss that?

You don't need pull up resistors. Either the ACORN has pull ups or drives the signals high and low. In your case, the DB25 outputs are driven high and low by the output chip.

Pin 4 should be high and pin 12 low on your AM26C31s to enable their outputs.

[cncman172]

eng199,

What device are they using now on the Acorn for the push-pull drivers. I have an earlier board and it does have pull up resistors.

Russ

[kentonsj]

I spent a lot of time last night reading about TTL and push/pull drivers. This circuit board experience has taught me a lot. Anyway...

I took a closeup pic of the DB25 connector and the IC's in the area. To me it looks like the push/pull driver is a ACT125G.

[eng199]

ON Semiconductor MC74ACT125DR2G

[cncman172]

Yeah this is just a driver that can be tri-stated making the output go to HiZ.

Attached spec page.

Russ

[slodat]

Considering converting my cnc router to DYN4 servos. After reading this thread and Jerry's, it has me scratching my head a little. Do I need these differential drivers? If so, I'm interested in one of your excess boards if you are selling.

[cncman172]

Slodat,
You can use these boards from CNC4PC. You need one of these for each driver. So if you have on axis with two motors then you would need two for that axis. They are cheap. They make two versions, one has screw terminals and the other has press in connections.

Someone is having a custom board that adds all the axis in one card.


https://cnc4pc.com/differential-line-driver.html

https://cnc4pc.com/c72-differential-line-driver.html

Russ

[slodat]

Making sure I’m following.. this differential driver is needed(?) for noise issues in the step/direction signals between Acorn and DYN4 drive?

[kentonsj]

Making sure I’m following.. this differential driver is needed(?) for noise issues in the step/direction signals between Acorn and DYN4 drive?

Slodat,

The differential driver is not explicitly required. There has been some chatter on the forums of how electrical noise in control panels is affecting the step signal into the DYN4. The DYN 4 does seem work fine with the recommended Centroid wiring diagram, if you are careful to follow shielding recommendations and layout your panel to separate the Acorn step wiring from high voltage and current. I chose to make a board to allow for custom cable connection for a couple of reasons. They are:

1. The DYN4 does accept a differential input, which is less susceptible to noise. I figured I would just go this extra step to avoid potential issues. To be clear, it sounds like most people don't have issues using the step/direction wiring as indicated in the Acorn to DMM wiring schematic.
2. I'm really OCD when it comes to wire routing and panel neatness. I figured this custom board would allow me to have a nice clean installation.
3. I wanted to try and have a custom circuit board made as a learning experience.

It will be cheaper and easier for you to order the CNC4PC boards and you gain all the differential signal benefits with a lot less work. Follow this thread for how to do that.
viewtopic.php?f=60&t=2610

Once I get my prototype boards. I'll solder one together and bench test. I'll have a couple extra boards. DM me and we can arrange for you to have one, if you wish. I may also just share the Gerber file so people can order the boards themselves. It might be cheaper to order more boards than it would be for me to mail from Canada.

Scott

[kentonsj]

Made some progress yesterday on my circuit board. I used a friend's reflow oven to solder the SMD components on. I made the cable from the Acorn DB25 connector to the differential step breakout board. I'm hoping to get a chance to test that the board works this weekend.