Go Down

Topic: Connecting a relay? (Read 4802 times) previous topic - next topic

polishdude20

Ok so I connected my relay to a transistor and all and it produces a clicking noise whenever the base is HIGH. But now I need to know which pins to connect an LED or motor to. Just tell me the names not locations, I know where they are but not what to connect to them.
Com, NC, or NO and such.

retrolefty


Ok so I connected my relay to a transistor and all and it produces a clicking noise whenever the base is HIGH. But now I need to know which pins to connect an LED or motor to. Just tell me the names not locations, I know where they are but not what to connect to them.
Com, NC, or NO and such.


Com (common) and NO (normally open) are the relay switch contacts that one normally wires the load to be controlled to. That way when the arduino output pin goes HIGH the relay coil energizes and that causes the the Com and NO contacts to close, allowing current to flow in your controlled circuit.

Normally open means the state of the contact when no power is applied to the relay coil, it's so called 'shelf condition'.

That enough information?

Lefty


CrossRoads

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Magician

There is a led on a board connected to pin 13.
Just insert digitalwrite(13, high), whenever you need it

polishdude20



Ok so I connected my relay to a transistor and all and it produces a clicking noise whenever the base is HIGH. But now I need to know which pins to connect an LED or motor to. Just tell me the names not locations, I know where they are but not what to connect to them.
Com, NC, or NO and such.


Com (common) and NO (normally open) are the relay switch contacts that one normally wires the load to be controlled to. That way when the arduino output pin goes HIGH the relay coil energizes and that causes the the Com and NO contacts to close, allowing current to flow in your controlled circuit.

Normally open means the state of the contact when no power is applied to the relay coil, it's so called 'shelf condition'.

That enough information?

Lefty




so with the LED I connect the negative pin to com and positive to NO?

CrossRoads

How about this?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

retrolefty

#6
Mar 05, 2011, 05:33 am Last Edit: Mar 05, 2011, 05:38 am by retrolefty Reason: 1
Quote
so with the LED I connect the negative pin to com and positive to NO?


Of course not. Doesn't a LED need a voltage source to work? Doesn't an LED need a series current limiting resistor to set the LED current to a proper value for the voltage you are using to power it? Relay contacts can not provide voltage or current. Relay contacts act just like a simple on off switch, they are a passive component.

I assume the LED you are using is just an example load for the relay? I ask because you can drive most standard LEDs directly from a arduino digital output pin using a series resistor to set the current draw to 20ma or less.
The transistor stage you are using could also drive a LED/resistor string without needing to use a relay at all. Relays are usually used where you need the higher voltage and current ratings that some relays contacts can provide.

CrossRoads posted you a nice schematic drawing (reply #5) showing a typical relay circuit including the load it switches on or off. Maybe you need to be more detailed on what you want to do and why you want to use a relay to do it>

Lefty

polishdude20


Quote
so with the LED I connect the negative pin to com and positive to NO?


Of course not. Doesn't a LED need a voltage source to work? Doesn't an LED need a series current limiting resistor to set the LED current to a proper value for the voltage you are using to power it? Relay contacts can not provide voltage or current. Relay contacts act just like a simple on off switch, they are a passive component.

I assume the LED you are using is just an example load for the relay? I ask because you can drive most standard LEDs directly from a arduino digital output pin using a series resistor to set the current draw to 20ma or less.
The transistor stage you are using could also drive a LED/resistor string without needing to use a relay at all. Relays are usually used where you need the higher voltage and current ratings that some relays contacts can provide.

CrossRoads posted you a nice schematic drawing (reply #5) showing a typical relay circuit including the load it switches on or off. Maybe you need to be more detailed on what you want to do and why you want to use a relay to do it>

Lefty



Ok crossroad's schematic helps but when I connect the LED to the  comm pin and then to +5 v , and the NO pin to ground then  the LED doesn't turn on even when I hear clicking. but, when I switch the ground from NO to NC then the LED ALWAYS stays on. Shouldn't it stay on only when the relay is off and not clicking?  I basically want to connect a motor to the relay and such but I'm starting with an LED for basics

retrolefty

Quote
Ok crossroad's schematic helps but when I connect the LED to the  comm pin and then to +5 v , and the NO pin to ground then  the LED doesn't turn on even when I hear clicking. but, when I switch the ground from NO to NC then the LED ALWAYS stays on. Shouldn't it stay on only when the relay is off and not clicking?  I basically want to connect a motor to the relay and such but I'm starting with an LED for basics


If your symptoms are accurate, something is wrong somewhere and it's difficult to troubleshoot over the net. Can you draw out a schematic of how you actually have everything (arduino, transistor, relay, led, resistor, external power)?  Also a link to your relay datasheet might be helpful.


polishdude20


Quote
Ok crossroad's schematic helps but when I connect the LED to the  comm pin and then to +5 v , and the NO pin to ground then  the LED doesn't turn on even when I hear clicking. but, when I switch the ground from NO to NC then the LED ALWAYS stays on. Shouldn't it stay on only when the relay is off and not clicking?  I basically want to connect a motor to the relay and such but I'm starting with an LED for basics


If your symptoms are accurate, something is wrong somewhere and it's difficult to troubleshoot over the net. Can you draw out a schematic of how you actually have everything (arduino, transistor, relay, led, resistor, external power)?  Also a link to your relay datasheet might be helpful.




ok I drew out a schematic sort of but I don't think I have a datasheet for the relay.

retrolefty

Quote
ok I drew out a schematic sort of but I don't think I have a datasheet for the relay.


Then the relay manufacture name and model number of the relay?

Lefty

polishdude20


Quote
ok I drew out a schematic sort of but I don't think I have a datasheet for the relay.


Then the relay manufacture name and model number of the relay?

Lefty



Midland Ross, Midtex Division, coil 24vdc , 190-22C100, B8211 .....thats all there is written on it.

polishdude20


If the coil is "24VDC" then it will almost certainly not operate with 5VDC.


so i guess that means it switches at 24vdc..

retrolefty

Pretty much a show stopper unless you can test with a 24vdc power source. If you do test at 24vdc be sure to remember to recalculate the LED's resistor size for the higher voltage.

Lefty




retrolefty



If the coil is "24VDC" then it will almost certainly not operate with 5VDC.


so i guess that means it switches at 24vdc..


Yes, and at 5vdc, you are hearing a small click but the relay coil has not enough power to actually pull the armature and contacts closed.

Lefty

Go Up