First Look: Cheap Parallel Port Opto Isolator Board

Being a lazy so & so ATM how much of delay would one get by using an opto-isolator to activate a second one (as in a lot of stepper motor drivers). Obviously there are opto-isolators and there are opto-isolators. I know this question has a lot of "depends" but there are some pretty slow opto-isolators out there, which maybe ok for input\output.

Just a thought I've had for bit.

Fifteen is a fair amount of CNC machines : )

I think I finished the wiring on the interface board. I didn't know what size cable I was going to use, so I didn't put a design in the housing.

I had an old USB able from an old webcam I was going to use to power the interface. It was resistive, losing about a volt over the length of a meter/yard. My roommate and I both considered that the cellphone switching power supply I tested it with might not put out 5 volts until there was a load on it, but the USB cable was indeed resistive.

Shaking my head, I held the end of an almost new USB extension cable in a pair of cutting pliers. Chop! I tinned the leads, drilled a hole in the housing, and worked for 15 minutes to cram a Harbor Freight crappy grommet in the housing. I put a zip tie on either end to use as a strain-relief. The new cable puts out 5 full volts.

After that, I eventually got the computer going. There is a surface mount power LED on the interface board.

I was able to test the limit switches. I have just a loop of wire right now for a hardware to software estop signal, but my machine has a hardware relay estop. I still want to get the hardware to software one going.

Anyway I have an HAL estop signal of FALSE, but I can't take LinuxCNC/Axis GUI off of Emergancy Stop to turn it On.
I posted a thread here:
forum.linuxcnc.org/24-hal-components/345...s-power-in-linux-cnc

Anyway, the inputs seem to be working, so I am making progress : )

If this is the best I can get from the board. I'm considering it a do not buy.
I may try another power source, perhaps another cable, but I thought this thing had shmidt triggers in it.

Just out of interest what is the part number of the optos ?

There is C519 printed on them. Not quite NECs. I had hoped that they would have worked. I don't know where else to get a board with this alleged functionality because I needed something very generic for my application.

A lot of the boards that are on the cheaper side tend to use a slower opto.
Roll you own with kicad and then get pcb's made. You might even be able a sell any extras.
I've used these guys in the past with excellent results about a 2 week turn around to Australia.
www.elecrow.com/

Some good info here on design:
www.anderswallin.net/2006/08/optoisolato...mesa-5i20-servocard/

Mesa also sell a card...might be a bit over kill for your needs.
store.mesanet.com/index.php?route=product/product&product_id=93

I am disappointed with the interface card at this point. The card is not doing what it's supposed to.

The instructions are have nice pictures, but the ChinEngrish does not read well.
Looking at the blurry output schematic, it looks like the voltage is pulled up with a resistor, and the opto-coupler pulls it down.

Aside from the rounded corners, I think what's going on is that the resistor pulling the output pins high is too high of a resistance to drive the driver optos. While it has 4+ volts swinging in the breeze, as soon the opto in the front end of the stepper driver sinks some 10 lousy MA, it pulls the voltage down to around 1.7 volts, that is not going to drive the optos in the stepper driver because they have a current limiting resistor, to work with 5 volts.

I suspect that by pulling the jumpers, the optos can be driven by a higher voltage, that might raise it's output, but I will have to drive it at 7 volts to get 5 out. As far as I can tell, the board's output is supposed to be isolate, or they wouldn't have included the jumpers to disconnect the power rails.

I never appreciated the Aduino's outputs until I ran into this thing.
I don't have the resources to come up with my own opto board, but if I did it would have replaceable optos, and good instructions.

I PM'ed some here about the board. I also sent a message to the ebay seller of the board. I figured the seller might want to get involved in this, send me better instructions, you know, to protect his rating : )

This was not the turn-key opto board solution I was looking for.

I got it working!!!

: )


Low voltage was the problem. I pulled the jumpers from the board, and at first I tried 9 volts. Checking the oscilloscope, the voltage output was over 2 volts. Half of the motor directions worked.

Then, I used a 12 volt power supply, putting a diode in line to cause a voltage drop, dropping to around 11 volts. Now, all the motors and directions work!

Thank you in no particular order: Andypugh, Tommylight, Grotius, Ozzyrob, PCW, Todd Zuercher, and Rodw, others, and for LinuxCNC.
I will shoot some video in the morning.

@Hi Brenda,

Nice to hear your machine is working !!
The best is to use the - step as signal from motor driver to your brake out board. Some motor drives will not work with + step signals.