Need Help!- Question about Optical home switches

[Dylwad]

I gathered up a few Omron EE-SX673's from a friend http://docs-europe.origin.electrocom...6b800b4c3a.pdf And plan on using them as home switches for DeskCNC, which expects N/C mechanical switches.

My question regards the spec sheet, it says when using the switches for logic to put a resistor between + and Out, called Rl, but doesnt specify a value.

Am I to assume they want you to use a value to get 100Ma or less across + and Out to simulate a relay coil? or does 40Ma sound right for Logic?

Do I really need a resistor at all

Thanks for the help,

I used them on a friends machine years ago, but just drove small DPDT signal relays to pull the inputs to ground, worked great, but I know theres a way to do it without the relays.

Dylan

[Pandinus]

The output is an open collector...

If a relay is attached to the output and +V, the transistor will sink current to 0V which activates the relay...
If you are driving a logic input, you need a resistor to pull the voltage up when the transistor is not biased.

I think what it is saying is if your pull up allows 40mA the output will drop to 0.4V which pretty much satisfies TTL logic levels (3.3V=high 0.35V=low.) And driving it with more than 40 mA will raise the low level output.... so 5V in and a ~125 Ohm resistor for "TTL"

If you do that and add a resistor at the output to the base of another NPN transistor, maybe use a darlington, emitter to 0V and your CNC input to the collector I think it should pull the signal low until the switch is triggered which would drag the "TTL" level to .4V and stop biasing the darlington allowing the signal to float...

[Al_The_Man]

Also If inputing to sourcing type input such as an opto or other type of input that has a pull up resistor built in, you do not need to add the resistor.
See the NPN sinking example.
Al.

[Dylwad]

Thanks guys,

As far as I can tell, the Deskcnc controller board has no opto isolation or pull up resistors, the wire traces go directly from the I/O header pins to the MCU. http://www.cncitalia.net/shop/images...Controller.jpg I wont know for sure untill I get my hands on it though.

It would be nice if DeskCNC would provide more info about things like this, It is good to see they just updated the software a week or so ago and added alot of new features, now they just need to update the documentation!

Ill try the 125 ohm resistor to start.

Would something like this http://futurlec.com/DC_Opto_Input_4.shtml work for opto-isolation?

Dylan

[Pandinus]

You could just add an opto-isolator IC like this...
just change he resistor to give what tge opto needs at your Voltage to the opto-sensor...

[Al_The_Man]

Originally Posted by Dylwad As far as I can tell, the Deskcnc controller board has no opto isolation or pull up resistors, the wire traces go directly from the I/O header pins to the MCU. Dylan

This is a pet beef of mine, many DIY BOB manuf. do not include how the input is conditioned etc.
This would not be tolerated on most industrial equipment of the same type.
Al.

[Dylwad]

I think I'm going to chicken out and just run the opticals to relays, I have the relays, just need flyback diodes. Much easier to wire than any other means, and I know its safe for the controller and switches.

Thanks for your help.

Dylan

[vger]

Hey Dylan,
The opto switches are essentially opto-isolators themselves. Also, it's pretty easy to grab power for the opto switches from inside the computer. You could even use a spare USB port to provide the needed 5V. And if you use the power and ground from the computer without connecting to other equipment, (just like your mouse and keyboard do) there is no need for isolation. I've pulled 5V (and GND) from a computer more than once using an old mouse cord with the mouse cut off.

TTL standards are pretty forgiving. For 74LSXXX (low power schotkey version of TTL) basicly, for inputs, anything over 2 volts is a logic high, anything under 0.8 volts is s low, and for outputs, a logic high will be at least 2.7 volts, and a low will be less than 0.5 volts. As for input current, it will be less than 1 mA. Early TTL circuits interfacing with open collector outputs used a 4.7K pullup resistor to satisfy that less than 1 mA input while keeping power use at a minimum. Seems when you have thousands of individual TTL circuits, all those little 1 mA current drains add up to Amps.

Enjoy
Steve

[Dylwad]

Thanks Steve,

The Deskcnc controller uses a serial cable to link to the computer, I tried sharing grounds with the controller and switches way back when, and it didnt work too good, once we gave the DeskCNC controller its own power supply all problems went away. Electronics can be touchy sometimes, even when properly shielded.

I have the relay board all wired up and tested, and the rest of the machine parts on the way. Hope to be cutting by the end of the month.

Thanks again,

Dylan

[pfred2]

Hey Al does your pet beef have a name?

Here's an undocumented DIY controller for you:

http://www.imagechicken.com/uploads/...2086495500.jpg

Unless I link to this:
http://img11.imageshack.us/img11/1819/ppbb4sch.png

I always thought I had a fair grasp of sourcing and sinking currents until you confused me with that PDF you posted! I'm sure you meant well ...

heh j/k I just had to reply to someone who has a pet beef! MOOO!