Why is relay power labelled "JD"?

I've seen numerous schematics such as this one which label relay power as JD-VCC.

What does the "JD" stand for?

I suspect it's to distinguish input VCC from VCC the other side of the jumper.

Riva:
I suspect it's to distinguish input VCC from VCC the other side of the jumper.

Hehe yep I understand the purpose, but wondered why "JD" as a label.... why not "PQ" or "XF". Wondering if the letters actually have a meaning. I see on one board the label was "RY-VCC" which obvioulsy means "RelaY", but why "JD"?

JimboZA:
......which obvioulsy means "RelaY", but why "PQ"?

Jim, I think you mean "...but why "JD"?"
(I'm waiting to hear the answer too. I've racked my brain and can't think what those letters stand for either. :confused: )

And it looks like you have your own personal spammer - YAKOKO. :smiley:
(Reported) .... Gone. :slight_smile:

Maybe it came from "jumper" D or "jack" D on some board and just stuck, whats the Chinese word for "Relay"?

Jumper-derived?

Just Dumb?

But with the weird opto but not really isolated design of those boards I think even the Chinese who designed it doesn't know why JD-Vcc...

OldSteve:
I think you mean "...but why "JD"?"

I did yep

septillion:
the weird opto but not really isolated design of those boards

Why are they not really isolated?

If the opto led has its anode from Arduino 5V and cathode to a low digital pin, which would activate the opto, and the relay coil has its own 5V (the JD one) and ground nowhere near the Arduino ground, surely that's fully isolated?

Okay, they can be used isolated. But a lot of people will just think, "Hé, it's got a opto coupler, must be isolated. Great!" But no, you have to weirdly feed it via a jumper on the other end of the board. Jumper should be just a jumper. Why couldn't they just add an extra terminal. And what do you connect where? Do you connect Vrelay there or Voptocoupler?

But worst think, most are on by default! No problem with active LOW but there is NO way to turn the relay off when the opto side is shut down [facepalm]

Agreed, pita to configure, not exactly intuitive.

It's strange that none of the sellers document how to isolate the power supplies even though they make a big deal of it having optocouplers. I agree it's annoying to wire the things. I want to use a single connector for the whole module but instead need to have an extra connector going over to that single pin which just doesn't seem as secure.

outsider:
, whats the Chinese word for "Relay"?

Zhōng jì

Reverse translation Relay station.

Many possible translations , i suspect you have to be Chinese to understand the usage.

jiē i think is the word for jumper but its normalyl used as part of another word

Whoever wrote this on the post you linked apparently doesn't know electronics:

However, to activate it you should provide the VCC with +5V. The GND connected to the GND and give a +5V signal to the IN1 or IN2 to activate it. IN1 and IN2 should be connected to one of your output pins, they will be able to switch your relay. But when I look at the schematic passerby send you it might also be possible that you'll have to put your output pin to LOW in order to activate it.

I think that's obvious, isn't it, based on the way it's wired .

septillion:
But worst think, most are on by default! No problem with active LOW but there is NO way to turn the relay off when the opto side is shut down [facepalm]

No, all relays are off (de-energized) when the opto side is shut down. VCC shuts down too ... where's the power coming from?

No, not on by default ... on powerup, pins default to HIGHZ (all relays off).
User's code establishes initial state in setup.

2 methods to startup with all relays off:

pinMode(relayPin, INPUT_PULLUP);
pinMode(relayPin, OUTPUT);
digitalWrite(relayPin, HIGH);
pinMode(relayPin, OUTPUT);

Re: Why is relay power labelled "JD"?

My guess ... from the schematic,

the Jumper connects VCC to the cathode of the flyback Diode, hence JD-VCC.

dlloyd:
No, all relays are off (de-energized) when the opto side is shut down. VCC shuts down too ... where's the power coming from?

From the isolated power source JD-Vcc.

If the relays are really de-energized when you leave the INx connection unconnected then I apologize. That means there are even more weird and beautiful versions of relay boards then I thought. The one I've used you had to turn the opto on (by pulling IN LOW) to turn the relay off. Leaving the opto off (by floating the IN) the relay would turn on. So assumed all opto relay boards had this. If not, then the board isn't as bad as I thought but be warned, some may be.

I agree with Dloyd. If you look at the schematic, it is clear that an opto isolated relay board would need a LOW to sink the opto led current, so that's no surprise. Second, if the opto output transistor sinks the coil current, the relay can't be on if the input is OFF. If you think about it, is becomes quite clear that people with no electronics understanding would configure their GPIO normally and ASSUME the IN would require a HIGH, consequently, their digital output, being set LOW by default in setup, would turn the relay ON, until their code sent a HIGH. With the IN floating , the opto led has no current and is off and thus so is the photo transistor. That's just physics. That's just the way it is.

Then I do sincerely apologize!

In the past I can across an opto relay module (it wasn’t my so I can’t show you) that was a little bit different. The schematic is attached.

As you can see, then the relay is turned on when the the input is disconnected. And because of this I assumed all those opto relay modules where connected like this. But I took a look at the schematic of JimboZA (didn’t before because I thought I already knew it ::slight_smile: ) and that showed it’s a bit different. So I was wrong of thinking is is active if it’s detached. Then the board isn’t as bad as I thought it was :slight_smile: Al tough I still hate the layout (feeding JD-Vcc via a jumper on the other end…) and I still think a isolated power supply for the relay is completely unnecessary (in 99% of all cases). But on the plus side, that would fix the “weird connection problem” because you can leave the jumper in place :stuck_out_tongue:

So again, sorry for all the confusion in this topic!

Hmmmm this has turned into an interesting discussion in spite of there (probably) being no answer to my actual question :slight_smile:

These sensor modules / shields are a bit of a mish-mash.

JD

Maybe Joint Drivers.

Because all the relay drivers/transistors are powered from that point.
Leo..