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Using Arduino => General Electronics => Topic started by: chodges on Nov 01, 2019, 06:28 pm

Title: 5 channel relay, no idea what the ports mean
Post by: chodges on Nov 01, 2019, 06:28 pm
Hey everyone,

I don't know much about relays, but I am using one for one of my projects. I got it yesterday, and I have no idea what the ports mean. They're completely different from all of the other relays I'm seeing in tutorials and stuff. There's DC+ and DC- power, but no ground. The Amazon description also doesn't make much sense to me.

Any help from someone with experience using these kinds of relays would be greatly appreciated! :)

https://www.amazon.com/5-Channel-Control-Trigger-Indicators-Arduino/dp/B07GCDTZWG/ref=sr_1_2?keywords=10+amp+relay&qid=1571172722&s=electronics&sr=1-2
Title: Re: 5 channel relay, no idea what the ports mean
Post by: DVDdoug on Nov 01, 2019, 07:23 pm
This is what happens when you buy cheap stuff on eBay, Alibaba, or from flakey 3rd-party Amazon suppliers.

Probably...
-DC is ground.   +DC is +12V (those are 12V relays).

C1 - C4 are the 5V control-signal inputs.
Title: Re: 5 channel relay, no idea what the ports mean
Post by: TomGeorge on Nov 02, 2019, 05:40 am
Hi,
Note the control input for the relays is, LOW to activate.
(https://forum.arduino.cc/index.php?action=dlattach;topic=644007.0;attach=331102)
Tom... :)
Title: Re: 5 channel relay, no idea what the ports mean
Post by: Paul__B on Nov 02, 2019, 02:14 pm
(https://forum.arduino.cc/index.php?action=dlattach;topic=644007.0;attach=331027)

C1 - C4 are the 5V control-signal inputs.
Note the control input for the relays is, LOW to activate.
So here is the problem.

If it is LOW to activate, LOW would be referenced to +12 V.  Which means a logic 5 V HIGH would by comparison with 12 V, be LOW and it could never not be actuated.  Yet they claim it can be microcontroller-controlled.

That is where the lack of either a circuit diagram, or proper instructions makes it difficult.  :smiley-eek:
Title: Re: 5 channel relay, no idea what the ports mean
Post by: herbschwarz on Nov 02, 2019, 03:24 pm
It seems that there are driver transistors included for 0-5V activation of the relays.
Title: Re: 5 channel relay, no idea what the ports mean
Post by: gilshultz on Nov 02, 2019, 08:22 pm
The following is my opinion as I do not have any documentation to properly check it, only what I can see from the picture and description from a seller that did not know what he was saying.  Personally I would send it back, the relay coils appear to NOT be isolated from the micro and can be a source of noise, transients and other confusing problems.

Without a schematic I can only guess.  There are 5 transistors on the board, I assume they drive the relays but that is only a guess.  They indicate a blue light which appears to the the converse of the input, if that is correct the transistor would probably do the inversion from the input and drive the LED. The inputs would be connected directly to the base of the relay driver transistor or to a pull up from the 12 Volt supply.   When they say port they typically mean an Input or Output pin of the microprocessor. On the Arduino they are the "D" digital pins. They state" Relay low-level pull-in, the module contains current-limiting resistor, possibly to the base of the transistor, the low-level can be DC-,  the microcontroller ground.  You would set microcontroller I / O port to low to turn off the relay, again guessing as I have no circuit." You can buy a properly isolated eight channel unit from china on ebay for several dollars less then what you spent on this one.
I think that is there way of telling you you need a LOW on the port ("D") pin. I would be cautious as if the ground connection between your Arduino and this board opens very weird things can happen and possibly damage the Arduino. 
Best guess the circuit is a transistor with the emitter connected to -DC, The collector to the relay coil and the other coil connection connected to DC+. If this is correct a high on the arduino port ("D") pin would turn the relay on.
Good Luck, and Have Fun!  
Title: Re: 5 channel relay, no idea what the ports mean
Post by: Paul__B on Nov 03, 2019, 08:16 pm
It seems that there are driver transistors included for 0-5V activation of the relays.
Obviously there are, but the description claims "low level activate".

If this means pulling down to ground (negative) to actuate, then this means the transistors with a 10k base-emitter resistor and a 4k7 driving the base, are connected emitter to the positive 12 V rail and will be switched on by any level a few volts less than that 12 V.  And they are, as a 2907A (https://www.onsemi.com/pub/Collateral/PZT2907A-D.PDF) is a PNP.

So a HIGH output from 5 V logic, at 5 V will be a LOW to the 12 V system and you cannot turn the relays OFF.

(Relay coil 400 Ohms, requires 30 mA, 4k7 base resistor gives 1.4 mA at 7 V, just sufficient to saturate transistor.)
Title: Re: 5 channel relay, no idea what the ports mean
Post by: TomGeorge on Nov 04, 2019, 07:11 am
Hi,
To check the input pins on the relay module.
Connect 12V to the two DC terminals and with DMM negative probe connected to DC-, put the DMM positive probe on one of the C terminals take a reading.

It should read about 12V or a bit lower.

Tom... :)