Pages: [1]   Go Down
Author Topic: 2v output on arduino  (Read 1624 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 22
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

hi i have my arduino output pin connected to a relay, but it is only giving me 2v from output pin? i need 5v to switch the relay
Logged

Global Moderator
Boston area, metrowest
Offline Offline
Brattain Member
*****
Karma: 544
Posts: 27352
Author of "Arduino for Teens". Available for Design & Build services. Now with Unlimited Eagle board sizes!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

What is the coil rating on the relay?
If its less than 150 ohm,  it needs more current than the Arduino can supply.
Use an NPN transistor to sink current thru the coil to turn it on.
Logged

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

0
Offline Offline
Shannon Member
****
Karma: 214
Posts: 12406
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

And very importantly you need a backwards diode across the relay coil to prevent damage - this is not an optional component - see the various examples on the arduino website of driving inductive loads like relays / motors.
Logged

[ I won't respond to messages, use the forum please ]

Offline Offline
Newbie
*
Karma: 0
Posts: 22
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

hi coil resistance is 320 ohms
Logged

Global Moderator
UK
Offline Offline
Brattain Member
*****
Karma: 308
Posts: 26465
I don't think you connected the grounds, Dave.
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Did you remember to make the pin an output?

Please feel free to chip in with details. Code, schematic, you know, the usual.
Logged

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

0
Offline Offline
Shannon Member
****
Karma: 214
Posts: 12406
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

If the coil resistance is 320ohm and the pin only pulls up to 2V the chip is fried. Probably destroyed by inductive kickback if there was no diode.
Logged

[ I won't respond to messages, use the forum please ]

Offline Offline
Newbie
*
Karma: 0
Posts: 22
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

i check the voltage coming out of the pin at 5v when it is on, but once i connect it to the relay and check voltage again its only 2v and my relay needs 5v to switch. the relay has already got a diode in parallel with the coil for protection so chip isn't fried.
Logged

Global Moderator
UK
Offline Offline
Brattain Member
*****
Karma: 308
Posts: 26465
I don't think you connected the grounds, Dave.
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

See reply #4
Logged

"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

0
Offline Offline
Shannon Member
****
Karma: 214
Posts: 12406
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The built-in pull-ups are spec'd as between 20k and 50k, the relay is alleged to be 320 ohms, there's no way that makes a potential divider of 40%!

If the load on the pin is really 320 ohms then the chip is fried since it would produce about 4.5V into that load.

A good measurement to make would be the current into the relay winding when directly connected to 5V supply.  If it reads about 15mA then it is 320 ohms and the output pin is blown (assuming no other load on the pin). 
Logged

[ I won't respond to messages, use the forum please ]

Pages: [1]   Go Up
Jump to: