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Forum Index : Microcontroller and PC projects : Interfacing Relays

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JohnS
Guru

Joined: 18/11/2011
Location: United Kingdom
Posts: 3678
Posted: 04:51am 23 May 2016
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How about 3V3 signal input if the LED is bypassed (shorted out)?

I think the boards I've seen were
In-LED-opto-R1-Vcc

JohnEdited by JohnS 2016-05-24
 
mikeb

Senior Member

Joined: 10/04/2016
Location: Australia
Posts: 173
Posted: 11:13am 23 May 2016
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Hi John,

You're spot on. The LED and resistor are in the order you state.
My bad !!! (and Geoff is down on himself when an 'odd' bug creeps in )
It would definately help to bypass the LED. A typical Red LED has a forward voltage
drop of approx 1V6 and a green LED 1V8. The relay board in question also has a current limiting resistor of 1K0 (R1-102).
Personally, I like the ULN2803 approach and a 12-24V DC power supply.
Phil, can you give that relay board a whirl and see what it does ? My guess is not much at 3V3 input. I'm always happy to stand corrected though.



Regards, Mike B.

There are 10 kinds of people in the world.
Those that understand binary and those that don't.
 
SteveP
Newbie

Joined: 21/03/2013
Location: United States
Posts: 19
Posted: 02:29pm 23 May 2016
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Depending on the load current and voltage, the relay can be replaced by an OptoMOS type device. Basically, a mosfet turned on by an internal led. The CPC1002N by IXYS is 60V, 700mA, 0.5 ohms On resistance, small 4 pin SOP package, only takes 2 mA to turn it on, costs $1.50 US. It basically acts like a floating resistor that changes resistance from very high to very low. It can act like a high side or low side optically isolated switch. Multiples of them can be used in series, anywhere along the voltage span between ground and the supply rail. It is unipolar output, I.e. Has a polarity. Other more expensive ones are bipolar. No back emf protection diode needed.

Steve
 
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