Problem with Relay experiment (Make: Electronics #7)

[OgreSwamp]

Hi there,

I'm reading Make: Electronics to recover my college electronics knowledge.
I've assembled a circuit (using a breadboard, during it with alligators is a nightmare) and it doesn't really work.

So here is a circuit I'm trying to do:



Here is what I've done:


Resistor is 680Omh, LEDs positioned properly (cathodes facing right - to the negative, green wires).
When I press red button (bottom left corner) I can hear the relay is switching, top led goes off, but bottom one doesn't start.

I've tried few things:
1) replace a relay component
2) replace LED
3) tried to measure voltage at 2nd led pins when I press red button

1 & 2 doesn't help.
Voltage goes up to 0.4-0.6 for half a second and then drops to zero when I press/release the button.
Can't figure out what's wrong. My only guess was that DPDT relay I've bought isn't the correct one, but I found the data sheet and it says that coil voltage is 12v - came as my circuit voltage.

Here are few more pictures to get a better understanding what's happen there.





Thanks!

[digsys]

Easy fix - check the drawing .. grobotronics.com/images/datasheets/HK19F-12V.pdf
Common is the centre pins are the pins NEXT to the coil ! Always check drawings, pinouts can vary a lot.

[peter.mitchell]

if that is real carbon fiber i'd avoid doing electronics work on it - its quite conductive.

[jahonen]

If all else is correct, it is possible that relay contacts are a bit oxidized and circuit voltage is too low to break through this oxide layer. This often happens if there is insufficient voltage/current through the relay to clean the contacts via contact sparking when switching happens.

Regards,
Janne

[OgreSwamp]

digsys, thanks! I switched red probe from the push button & non-working LEDs anode and now everything is working! That was one of my suggestions. I've checked drawing on the bottom of relay (it has it) but didn't quite understand it. Now I have much better understanding.

peter.mitchell - good spot. This is a soldering pad, so most likely it is a carbon fibre. I think for now I can work on the table but when I will start to do experiments with ICs I may buy a anti-static mat.

jahonen, thanks. I mentioned I've tried to change relay. Anyway thanks for the guess. I'll check in future that all contacts are clean.

Cheers!