Newbie Help with Input Status

[rossw]

Trouble is, how many peripheral boards do we need to add to connect to the real world to make a the credit card size  board work safely?

 
Trouble is really, there's no "one size fits all" solution.
Everyone wants to do something slightly different. Opto-isolated inputs are ideal for some, but completely unused for others and do nothing but add to costs.
 
The WC32 daughter-board has opto-isolators for each input channel.
It also has adjustable-gain amplifiers for each analog input.
It also has open-drain fet drivers for a few (4) outputs.
That board is getting fairly busy though, and its cost is somewhat higher than it needs to be if you don't want or need isolation, or the FET outputs, or the amplifiers!
 
I'm trying to get a little spare time to make another version of my WC8 terminal board which will include some optos etc, but it will be a while off yet.

 

[LarrylLix]

I'm trying to get a little spare time to make another version of my WC8 terminal board which will include some optos etc, but it will be a while off yet.

Nice!
 
Yeah, it's always a trade off for price, size, power consumption, etc...  A sit-on-top/below board with optional I/O buffering would be  great idea...with terminals for most I/O too.
 
We always want more once we absorb what we have so far.

 

[rossw]

Yeah, it's always a trade off for price, size, power consumption, etc...  A sit-on-top/below board with optional I/O buffering would be  great idea...with terminals for most I/O too.

 
http://webcontrol.rossw.net/ is my current board for the WC8. It has adjustable gain amps for the A/D inputs, screw terminals for inputs, at least it has spots to solder some limited input conditioning and a prototyping area where you COULD put a couple of optos... and it does sit on-top of the WC8, so it ticks most of your boxes!

 

[ccthbsh01]

Thank you all for your help,

Can you please give me a link to which optocoupler to get? As I mentioned I have very little knowledge about these electrical stuff. I thought this is just going to be plug & play, connect 8 sensors to the board, write the PLC code to update a variable on my ISY-994 using WEBSET upon change in the sensor status, and I will be good to go. Turns out I am learning a lot of things along the way with all your help.

Thanks again.

 

[ccthbsh01]

I suspect that due to the site being down last night, the notification emails did not go out. So I am posting this again. Thanks.
 

Thank you all for your help, Can you please give me a link to which optocoupler to get? As I mentioned I have very little knowledge about these electrical stuff. I thought this is just going to be plug & play, connect 8 sensors to the board, write the PLC code to update a variable on my ISY-994 using WEBSET upon change in the sensor status, and I will be good to go. Turns out I am learning a lot of things along the way with all your help. Thanks again.

 

 

[Tschmidt]

As far as opto couplers go you have two routes, industrial controllers typically use modular unit with interchangeable input and output modules but that can get pricy.
 
For AC output switching Solid State Relays (SSR) work great. One thing to be aware of with SSRs is they have a snubber circuit to protect the Triac or back to back SCRs. That can cause problem with very small loads. For example if you connect a typical neon pilot light to the load side of an SSR it stays on constantly due to the tiny amount of leakage.
 
Electromechanical relays (EMR) are also an effective isolating mechanism you will find lots of different relay boards on ebay.
 
For input isolation I typically use TIL117 or SPX53 opto because I have a drawer full of them. If I needed something low power or faster I'd use a more modern opto.
 
Do an eBay search for optocoupler and pick up a handful of transistor output (not triac output). If you don't already have one I'd suggest getting a breadboard, nice to be able to play around with a circuit before you have to spend the time to wire it up for real.
 
Unless you are trying to break ground loops you really don't need to use an opto.
 
/tom

 

[ccthbsh01]

Thank you very much Tschmidt for helping me. I will look into the various option you mentioned. I do have this 8 channel relay http://www.amazon.com/SainSmart-8-CH-8-Channel-Relay-Module/dp/B0057OC5WK which I think is what you mean with "Electromechanical relays (EMR)", so I will start with this first & try to figure out how I am supposed to hook it all up. Thanks.

 

[CAI_Support]

SainSmart relay boards are cheap, but they are actually negative triggered, which means, you will need to make sure if power to WC8 board lost, relay board does not malfunction.
 
Most industrial controller output is positive for logic TTL 1.  That protecting any accidental turn on output when power lost.
Someone reported this relay board is triggered by positive signal:
 

http://www.amazon.com/Generic-Channel-Extension-ArduinoTest-Develop/dp/B00GGKHZ7O

 

[CAI_Support]

opto coupler chip is very low cost:
 

http://www.ebay.com/itm/371082829954

 

[ccthbsh01]

Thanks CAI_Support,
 
 

SainSmart relay boards are cheap, but they are actually negative triggered, which means, you will need to make sure if power to WC8 board lost, relay board does not malfunction.
 
Most industrial controller output is positive for logic TTL 1.  That protecting any accidental turn on output when power lost.

 
I have seen on the web people mentioning this & complaining about it, including in the Amazon reviews. But I don’t really understand what the issue is. Isn’t this what the N/O & N/C connections on the relay are for? So you can connect your wire to either one, depending on whether you want it to be closed or open when the relay is off. Am I missing something? 
 
Thanks.

 

[CAI_Support]

The proper control system is that when power off or power on, the relay does not trigger.  If relay controls a heater, when power lost on part of the system, relay board could turn on heater by itself, then causes overheat or fire. 
 
In the industry control, it always require to have TTL 1 only to turn on relay, because most industrial system designed with power lost, it will not output TTL 1.  When xduino started, it did not think too much about this.  Then a lot of relay makers started making relay boards to fit its output, that is with output at TTL 0 level to turn on the relay. 
 
It is possible to rework those relay boards to reverse the input control signal to TTL1 turn on, by drilling out vias, cut traces, and solder wires.  Or simply get the correct relay board.  Another way to do it is to have one of the WC output to control a SSR which switch on the power supply powering the relay board, in that way without WC8 output, the relay board has no power to turn on the output.