Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Question about a DC Relay

Hawaslsh

Advanced Member level 4
Joined
Mar 13, 2015
Messages
102
Helped
5
Reputation
10
Reaction score
5
Trophy points
18
Location
Washington DC, USA
Activity points
1,279
Hello all,

I have been burned in the past when it comes to relys, so I wanted to ask and make sure my understanding of a particular relay was correct.
I am looking at the CPC1706 datasheet, It is a normally open DC relay.
my question is: can the LED be driven directly from an Arduino (Atmega328) output and would it need a current limiting resistor?
Also, Some relays require a zero crossing in order to fully turn off, Since this is LED driven MOSFET, that isn't the case?

Capture.PNG

Thanks in advance!
Sami
 

Carry for cents bazar

Member level 3
Joined
Aug 2, 2020
Messages
65
Helped
10
Reputation
20
Reaction score
13
Trophy points
18
Location
CZ
Activity points
360
This is an opto relay. It will need a current limiting resistor for the 1 and 2 pins, it can not be driven directly by the arduino, it will require a driver. This relay is not good, I recommend using a different one. Despite that the datasheet shows the voltage drop over the diode to be 1.2V to 1.5V, its not good to drive it from the Arduino pin. It takes a maximum of 50mA control current, which is too high for the Arduino. You can use a MOS 2n7000 or similar to turn on the relay and connect the MOS to the arduino pin. Like this you wont need a current limiting resistor, but its good to have one or to limit the current with a bipolar transistor.
 
Last edited:

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
18,034
Helped
4,045
Reputation
8,090
Reaction score
3,959
Trophy points
113
Activity points
119,058
Hi,

The input device is a LED, and as every LED it needs to be current limited.
You definitely need a current limiting resistor.

The LED needs at least 5mA, 1.5V to be ON.
Maximum LED current is 50mA.
To operate it at the minimum current is no good idea.
In the datasheet it is specified at 10mA... seems to be a useful value.

I didn't read the Atmega datasheet. Please read regarding "output characteristics"
There you will find whether it is able to drive 10mA .... and what the according output voltage will be.

The datasheet does not mention zero cross, thus don't care about it.

Klaus
 

dr pepper

Full Member level 5
Joined
Mar 15, 2010
Messages
259
Helped
33
Reputation
66
Reaction score
33
Trophy points
1,308
Location
lancs
Activity points
3,261
470 ohm in series with the atmel pin should do it.
 

Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top