2 RAs in tandem + H2O Automation

Talk about you and your tank/equipment

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PostPosted: Mon Mar 10, 2014 10:01 am
The trigger is whether you want the relay to activate when RA sends high (5V) signal or low (0V) signal.
If you set to low, the relay will activate when RA sends 0% or when RA is offline. That's the best scenario when you want something to be on when RA looses power.
If you set to high, the relay will activate when RA sends 100% (assuming you set the jumpers to 5V analog) and will not activate when RA looses power. So, the relay can only be activated when RA is operational and sending 100% signal.
That's what I picked up of what the trigger is.
Roberto.
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PostPosted: Mon Mar 10, 2014 10:16 am
But if it is a 24V relay will a 5v signal from the RA even trigger it?

The E-Bay description is very unclear what the high and low triggers do?
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PostPosted: Mon Mar 10, 2014 10:16 am
That's interesting and actually may match up to what I saw when initially testing....

I had the Low trigger option configured and initially when I wired everything up the relays were ON not OFF. Thats why I started screwing around with the wiring, etc. So I probably had good behavior and messed it up trying to unconfirm that behavior.

The Low option is almost what I'm looking to do with the signal from upstairs though so that's cool to know that other applications have similar requirement :)
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PostPosted: Mon Mar 10, 2014 10:19 am
Sacohen wrote:But if it is a 24V relay will a 5v signal from the RA even trigger it?

The E-Bay description is very unclear what the high and low triggers do?


The relays are made to work with Arduino.. here's the ebay link http://bit.ly/1pFisuu

I have a feeling that the voltage on that signal doesn't really matter except that it's good. The test code on the controller was slow so I may not have waited it out long enough thinking something was wrong with my wiring to see the ports come on / off.

I also wasn't sure I had the pinout properly on the RA so I was debugging that at the same time... at least I got an extra set of relays this time. I'll go one at a time and make sure I don't fry them all in one shot...

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PostPosted: Mon Mar 10, 2014 10:24 am
The signal IN is not directly connected to the relay coil. It goes through an opto-isolator, which in turn controls a transistor, which in turn activates the coil, which is 24VDC.
The purpose of the opto-isolator is to isolate the RA port from being damaged by anything that is going on with the relay coil stuff, which is running at 24VDC.
The opto-isolator does not have enough power to activate the coil in the relay, so a transistor is need that can handle the 24V and 5mA current.
Roberto.
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PostPosted: Mon Mar 10, 2014 10:40 am
Thanks for clarifying that. I had never heard of an Optocoupler before and wasn't sure what they did.

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PostPosted: Mon Mar 10, 2014 10:46 am
Check the beginning of the thread for the schematics of an optocoupler:
viewtopic.php?p=36132#p36132
It works basically the same as your tv remote control. On one side you have a infrared led (your remote control) and on the other side, you have a photo-sensitive transistor (your tv).
When the led is turned on by the RA signal, it emits light that the transistor picks up so you have this layer of protection where one side is isolated from the other side by a small gap of air.
This small gap of air protects one side from another since they don't have any physical contact and the signal is transmitted by means of light through this led-transistor combo.
Roberto.
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PostPosted: Mon Mar 10, 2014 10:48 am
Very cool. You learn something new everyday. :)

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PostPosted: Mon Mar 10, 2014 11:01 am
So I guess on the issue of high or low trigger, I couldn't find much documented.. I did find the specifications for one relay that said the low trigger was anything less than 7V and high was >7V.

I also found this link http://www1.electusdistribution.com.au/ ... tocoup.pdf

[quote]For example just like a discrete LED, you can drive an
optocoupler’s input LED from a transistor or logic
gate/buffer. All that’s needed is a series resistor to set the
current level when the LED is turned on. And regardless of
whether you use a transistor or logic buffer to drive the
LED, you still have the option of driving it in ‘pull down’ or
‘pull up’ mode — see Fig.2. This means you can arrange for
the LED, and hence the optocoupler, to be either ‘on’ or
‘off ’ for a logic high (or low) in the driving circuitry./quote]

And based on the behavior I saw (both relays going to ON when set to Low trigger) I'm pretty inclined to think that it was all working as expected and I screwed up it up trying to troubleshoot a working situation. Only one way to know once the new relays come in. I can't seem to find anyone in the US that sells these.. I found a few more links on Amazon, etc. but they all have crazy stupid shipping times. If anyone knows where I can source something like this locally, please lmk. In the meantime, I'm glad I have some confirmation that I was going in the right direction.
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PostPosted: Fri Mar 21, 2014 5:32 am
Got the replacement relays last night. Probably won't have time to connect and test them for a little while. Also received a delivery from Roberto. My dimming module.. so I can hack my D-120s and a salinity module so i can automate salt mixing :) I need to start working on the code for all of this soon...
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