SLA7062/67 Driver on Batchpcb

[rinthesun]

I have a prototype opto isolated driver on Batchpcb. The BOM and (circuit soon) are on my blog (cncrouterbuild.blogspot.com.) As soon as the board is tested I will post results here.

Products

The driver, besides being isolated, is fused and has an on board 5V regulator. The input uses the 10 pin IDC connector compatible with PMinMo and the CNC USB Motion Controller. Design is covered by CC-BY-SA.



On Batchpcb there is also a pcb for the CNC USB Motion Controller from Planet-CNC. The BOM is on my blog. Circuit soon.

Products

[James Newton]

Those are great, but I do have a few concerns and I'm curious how you feel about them.

- I personally don't understand everyone drive for opto-isolation... I prototype on an old expendable Windows '98 box and just run TuboCNC. Even if you want to hook up your top end laptop with Mach 3 to a machine, wouldn't the break out board (BOB) be a better place for the isolation? For example, the 4 axis BOB at PMinMO.com...

- Why include the 5 volt regulator on each axis. Again, that seems like something that should be an option on a BOB. There is a 4 axis BOB with a regulator (and no isolation) at
4Axis4: BOB/Pulse/Power(PC Board ONLY) just to show the idea.

- SLAs are hard to find and very expensive in low quantities
Find SLA7062 Stock and Compare Prices Across the Most Reputable Distributors in the Industry.. The knock offs are less, but unless you group buy them, they are really expensive. Are you planning on putting together a group buy?

- The PCB /alone/ is almost $16 plus shipping. For a bit over twice that, you can get a full kit of parts, less the opto and regulator at
SLAm1: SLA 7062M Stepper Motor Control kit
For about 4 times that much, you can get a 3 axis kit (with knock off SLA's) from Hobby CNC. What I'm saying is that I don't understand making the board design available only via a paid service. If you want to support hobbists, give us the gerbers. If you want to sell a product, your pricing is high.

- The Planet CNC board is great, but again the price: They already sell the PCB for $30 including shipping CNC USB controller. Your board from BatchPCB is $27 without shipping... which I assume is at least $3... probably more like $5.


I just didn't understand what you are accomplishing here... If you had redesigned the Planet CNC board to include optos and a regulator... but then you get 500mA +5 from USB...

I'm missing something, right? Don't take this as criticism, I'm honestly just asking what I've failed to understand.

[rinthesun]

Opto Isolation: Maybe you are not worried about an old desktop computer, but if the CNC electronics, say the CNC USB Motion Controller, is plugged into my expensive laptop, hopefully, the isolation may save it. A few dollars worth of parts. I have two other designs, L297/L298 and TB6560, using this same form factor with isolation. I started working on these after reading the extensive thread, in this forum, on the TB6560.

5 Volt reg: Because of the isolation. Several driver designs without isolation use a separate regulator for noise reasons. See that same thread.

SLA Availability: I needed three and had them in a few days. Can also use SLA7067. Some of the websites indicate that thousands are available in china. They seem to still be in production, so I do not understand the availability problem. They are a neat chip, especially for a thru hole design.

Batchpcb: I use them for prototypes. They charge $2.5 per sq. in. plus $10. setup and take 3 weeks. They have always sent me two boards for that price. I made them available for anyone who might be interested. Once they are tested, I may get some production pieces that will be much cheaper. I can provide the gerbers, but then unless you make them DIY you will still need someone like Batchpcb. I did not put them up to make money, but designed them for myself.

CNC USB Motion Controller: I am in Florida and pay $.88 for shipping. I want to use this device, but wish to make some changes and additions to the layout. They have given me permission to do this, since they are mainly interested in selling the PC code. I would estimate that a production pcb is like $10. or less. Once again, I am doing this for myself.

[James Newton]

Good points.

I think I may not have been clear on the opto isolation point. It isn't that I don't worry because I use and old PC: It's that I use an old PC so I don't have to worry. The extra cost and hassle of the opto's isn't worth it, in my opinion. I've never fried the old PC in years of dinking around, and I like the setup so much I doubt I'll ever connect to the laptop. But if you MUST use your top end machine... yes, it makes sense to isolate it...

But I still don't understand isolating on the driver instead of on the BOB or USB interface. If you short something between the isolation and the USB, it's still going to kill the laptop. Really, you want isolation at the USB cable:
USB Isolators, USB Isolation which will set you back $99 but will /actually/ protect your laptop.

How much did you pay for your SLAs?

I totally understand /your/ using BatchPCB, but if you want to share your work, please post the Gerbers / design files and let others decide which service they want to use? I'm sure people would appreciate that much more. Up to you of course, you did the work, you get to decide how to share it.

Thanks for the conversation! Good luck with the setup.

[James Newton]

I forgot to post this link: It's a USB isolator chip... not expensive and if it was added to the USB controller board, it would vastly increase the safety of your system:
ADUM4160 | Full/Low Speed USB Digital Isolator | Digital Isolators | Interface | Analog Devices

[rinthesun]

I paid $9.62 ea, but they are now out. They do have 72, SLA7067M at $12. ea.

I see that Mouser has TB6560 at $4. ea and, depending on your motor type, that may be a better choice. I still like the SanKen part and hope supplies pick up. The earthquake did not help.

I am an old time engineer and have a habit of over designing at least in short run projects. I started with a parallel breakout from PMinMo. Once I decided on isolation, it was either design a new breakout or place the isolation on the driver. Part count is the same with some more board space on the driver. To design it with isolation means a few dollars out of hundreds spent on the CNC router system. A reasonable trade off. That's my choice.

For those out there building a CNC system be aware the just because an integrated parallel port driver board says that it has isolators do not trust it. Inspect the circuit diagram. Elsewhere in this forum is a thread about a popular chinese TB6560 board that claims isolation but has a common ground from the motors to the parallel port.

[James Newton]

Yeah the prices and availability on SLA's have really changed lately. Maybe due to Japan?

Understanding that you have a non-isolated BOB that you are still using makes everything much more reasonable. I thought you were going to use the USB controller as a BOB.

If you continue with the USB project, do check out that USB isolation chip...

Best wishes and good luck!

[rinthesun]

Here is the schematic for my version of the Planet-CNC pcb. I started this layout based on a comment by PMinMo in this forum that the orientation of the 10 pin driver connector was such that a 180 deg twist was needed in the IDC cable. Since I do not have one of the Planet-cnc pcb's I do not know if this is correct; however, on this version it is correctly oriented. A 5V regulator has also been added along with a connector for mounting a panel USB connector. The ICSP connector has also been changed to match the PicKit2 pinout. Additional info is on my blog. cncrouterbuild.blogspot.com.