Using a transistor as a relay

[CocaCola]

In theory then the same design should work, make sure to bond all the grounds common between devices...

 

[StealthRT]

Well i tested this out and i'm not sure about the setup values.

At both times i get 0v when the 5v port is on (HIGH) or when its off (LOW) using a 330ohm resistor.

At this point it would seem it would turn on the pc even in the off (low) state?

Any ideas?

 

[CocaCola]

Post pictures of your circuit...

 

[StealthRT]

Its just as the image i posted shows.

 

[CocaCola]

Its just as the image i posted shows.

If it isn't working, then it differs from what was shown...

You either have made a mistake in hooking it up or laying it out...

 

[StealthRT]

Here is my current hookup:

 

[CocaCola]

Without getting into all the details, it appears the transistor is in backwards...

 

[StealthRT]

Its a radioshack brand... Its labeled With the FLAT end down...

 ----
(____)
3 2 1

Which is
1 = emitter
2 = base
3 = collector

So in the previous pic it was

1 = arduino gnd
2 = digital output > 330 ohm
3 = out to switch

 

[CocaCola]

Rat Shack is notorious for having improper labeling on their packages as they source new suppliers of the components and/or switch up to a new 'compatible' parts with no regard for any differences... Been there and seen it personally several times over the years, they really have become a joke...

Go down to the Sept 9, review here: http://www.radioshack.com/product/index.jsp?productId=2062586

And go down to the second review here: http://www.buzzillions.com/reviews/radio-shack-mps2222a-transistor-reviews

See a trend

So personally I would ignore their packaging and go with the common pin out if it is indeed a 2n2222...

 

[Rleo6965]

@stealthRT
Its better to to see the manufacturer datasheet.

Always verify all continuity of your component on a solderless breadboard. Most of the time there's a loose connection and resulting intermittent problem.

Once powered on. Test all voltage on important test point to identify abnormal voltage that cause circuit malfunction.

 

[StealthRT]

i get 0v when off and 0.01v when on...... That wont work since it would turn on the motherboard when the arduino is off or on...

 

[CocaCola]

Disconnect the 'pc' wires so it's no longer part of the circuit, take a volt meter, positive lead to +3 (or 5) that you are running the Ardunio from... Take the negative lead and connect it to the Collector of the transistor...

Now toggle the Base of the transistor high/low with the Arduino and confirm the volt meter jumps from 0 to +3...

If not take the positive lead of the volt meter and attach it to the Base of the transistor, and the negative lead to ground... Now toggle the base high/low with the Arduino to confirm the base is in fact getting toggled...

 

[StealthRT]

OK im going to switch gears here. I got a 5v relay that i will now be using.

I hooked it up and it triggers the relay closed when the digital output is high. And i have it feeding a gnd to the middle and the output pin on the relay is reading 0v. However when i hook that end up to one side of the switch and the other side to the arduino gnd it does not trigger the motherboard on once the relay is closed.

 

[CocaCola]

If you are using a relay, no need to bind the grounds, just make the outputs of the relay common to the switch... In other words take one side of the switch and connect it to one of the relay outputs, and connect the other side of the switch to the other relay output...

 

[StealthRT]

If you are using a relay, no need to bind the grounds, just make the outputs of the relay common to the switch... In other words take one side of the switch and connect it to one of the relay outputs, and connect the other side of the switch to the other relay output...

Care to draw that out?

 

[CocaCola]

 

[StealthRT]

WAHOOOOOOOOOOOOO!!!!! finally.

Thanks CocaCola