Jump to content

Driving 3V relays using MSP430G2553

Recommended Posts



I am trying to operate a 3V relay (from OMRON) using MSP430G2553. The relay is a SPDT one, with 6 PINs. I am not quite sure how to wire a6 PIN relay (I have some experience with 5 PIN SPDT relay), and I cannot find much information in the internet. I was also told that, for driving a 3V relay, I would not require transistor + diode combination. For your information, the relay has a rated coil current of 50 mA.


Can anyone help me on understanding the wiring structure of the relay? How to interface it with MSP430? Also, is it true that, I can operate the 3V relay without separate transistor + diode combination? 


I do not have much experience in microcontroller, particularly in MSP430 platform. Any suggestion is welcome. Thank you in advance for your support.

Link to post
Share on other sites

First, DO NOT directly drive it with the microcontroller without knowing more. The output of the microcontroller (any microcontroller, not just MSP430) can be damaged driving the inductive load and current demand of the relay coil if not done properly.


That said, it is tough to give details without having the part number for the relay, so I will give some generalities:


The recommended way to drive the relay is to use a transistor (an npn bipolar is traditional) as a switch to ground, and use a diode across the coil to shunt the inductive kickback when shut off. Directly driving is likely to damage or destroy the microcontroller, sooner or later, even with a protection diode. Not a guarantee, but, again, without part data, I would lean that way.


A six pin SPDT relay could be the same as a five pin, with one unused or a redundant connection (often the common for the switch), or could be a double coil. Need to know what the model is. A double coil is generally a unipolar latching type: trigger one coil to latch to the NO position, the other to release to the NC position. Gotta look at the data sheet to see if coil current polarity matters. Some do, some don't.

Link to post
Share on other sites

Sorry, my bad. I forgot to mention the relay model. 

It's a 3V relay from Omron, and the parts ID is: G5V-1.


Thanks for your suggestion regarding transistors. I would really appreciate if you could provide me a pointer towards similar example, which shows detailed schematic. 

Link to post
Share on other sites

OK... The data sheet (http://www. omron.com/ecb/products/pdf/en-g5v_1.pdf) shows that pins 5 and 6 are both connected to the common of the switch. Either or both can be used in your application.


Lots of examples for using a transistor to control a relay... They all pretty much are the same thing, since it is a basic concept that has been around since vacuum tubes, and pretty much anyone working with electronics learns it sooner or later.


Method one is build it from discrete components as in the crude attachment. Preferred for a single device. 2n3404 or 2n2222 for the relay you are using, a 2.2K resistor on the base (0.5mA base drive to insure saturation of the transistor for 50mA coil current), and any small sig diode for flyback (1n914 is fine)


Method two is use a driver IC, which contains multiples of this basic block, such as the ULN2003 or ULN 2004, or one of the hundreds of similar IC's (these particular ones are darlingtons, which means they can sink more current than a single transistor, but at the expense of greater potential drop.... There are also simple bipolar drivers)


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...