Centroid Community CNC Support Forum

cncman172 wrote: ↑Fri Jan 25, 2019 4:00 pm 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.

cncman172 wrote: ↑Fri Jan 25, 2019 4:02 pm eng199,
You could pull up the outputs to 5V, since those Acorn screw terminal outputs are open collector.

Russ

That would be a start, but there is still some signal degradation that can be avoided by using the DB25. This would only be an issue if running higher output frequencies is part of the goal when switching to line drivers.

kentonsj wrote: ↑Fri Jan 25, 2019 4:30 pm 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?

Yes, that is no problem. All the I/Os are always active. ACORN does not "know" which headers you are using.

cncman172,

That's great!

A couple more questions, if I may. Thanks so much for your help. Do you have a schematic of how you laid out your circuit board? I'm not 100% familiar with the semi-conductor world, and in the case of the AM26C31 I am not quite sure what I should do with pins 4 and 12. In the schematic from TI, pin 4 is grounded is that correct? It looks to me like you have a solder bridge across from pin 12 to Vcc. This would enable the AM26C31 as input low? As for the rest of the AM26C31, it seems pretty self explanatory, I need a 0.10uF cap on the input Vcc and I can connect 4 channels and get 2 axis worth of differential outputs from each AM26C31.

eng199,

I will use the DB25 connector to maximize chances of success.

YES, let me dig up the schematic and also the PCB layout. I actually made the PCB on my CNC machine. I used Eagle software to do the schematic and board layout and then used PCB2GCODE to convert the layout into gcode for the cnc machine. You just use an engraving bit and it removes the copper around what will become traces. I even have that code. You also use some very small drills to drill the holes for the connectors and components.

I will post this shortly.

Russ

Here is the schematic and board layout from Eagle which is a free PCB software available on the web. I have attached the last version of pcb-gcode if you want to play. In the zip file I have the Mach3 tap files used to machine a copper board into the PCB.

Russ

cncman172,

Thanks for posting that!

I think I will tweak my board a little to suit my setup. I have done some simple circuit boards on my first CNC router, but i had to get rid of it to make room for my new 5x10 Thermwood that I'm retrofitting. I'll have to order this circuit board, thankfully you can do that really inexpensively now.

Scott

Yeah, Scott I was going to send it to China to have the PCB made but unless you are making 30+ it is crazy. They do have some places now that will do 5 copies for pretty cheap.

I thought about modifying it to plug into Acorn directly but I had other things on my plate. That Thermwood will be a really nice machine when you get it finished.

Russ

For your PCB's I suggest painless, correct, coupla weeks - https://oshpark.com made here in the USA and excellent quality. They will take your Eagle or KiCad files directly and show you EXACTLY on-screen what will be made.

A little more trouble as you'll need to produce gerbers, and verify them yourself, but really cheap, pretty good quality and 2-3 weeks. https://allpcb.com

Here is my PCB, designed and ordered. I used EasyEDA and JLCPCB. It was $14US (shipped) for 10 boards. I didn't check the forums until this morning, so I missed the suggestion for OSH Park, next time:)

I decided to add headers with shorting blocks to enable selection of +5V or GND on pins 4 and 12. I know Russ had both of those pins to 5V, but I wasn't 100% sure that's what I'd want on my setup. I also added a header to connect my Y and slave enables together, as is shown on gantry squaring on the next release. My Z axis uses a holding brake when not powered, so I have the brake signal from the DYN4 pulled out to a terminal for connection to an outboard relay. The DYN4 takes care of all the timing of the brake, so Acorn isn't involved in that.

If this ends up working, I'm sure I'll have a couple boards left over. Someone with a similar set-up might want to use them. It should allow for a nice tidy installation. I'm using DB9 connectors on the my PCB and I'll buy some shielded DB9 cables. I need to solder one end to DB25 anyway, the pre-made DB9 cables are cheap.

Thanks again for the input and help!
Scott

eng199 wrote: ↑Fri Jan 25, 2019 5:30 pm

cncman172 wrote: ↑Fri Jan 25, 2019 4:00 pm 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?

Scott,
Just posted a reply your board looks great. Strange I submitted it and it never showed up. I had that happen a couple times the other day as well. Anyway nice layout and nice idea on the DB9 connectors.

Russ