How to add a two way switch to this circuit?

[saurabh9]

Hi,
Please have a look at the circuit at:
http://www.glacialwanderer.com/_blog/blog2008/04_April/hb_relay5.jpg.
It is from the article at http://www.glacialwanderer.com/hobbyrobotics/?p=9.

The circuit it to turn on or off a AC bulb by a microcontroller. My
question is, can we somehow safely add a manual override switch near
the bulb, so that even if the microprocessor is not working, we can
turn the switch on/off manually? If yes, how will the circuit then
look like?
Sorry if this is a simple question as I am just starting in
electronics and electrical circuits.

 

[Adrian C]

The circuit it to turn on or off a AC bulb by a microcontroller. My
question is, can we somehow safely add a manual override switch near
the bulb, so that even if the microprocessor is not working, we can
turn the switch on/off manually? If yes, how will the circuit then
look like?

You put a switch in parallel to the relay contacts.

Sorry if this is a simple question as I am just starting in
electronics and electrical circuits.

Sure. This is a simple question that involves basic technology of a
bulb, a switch and a power source. Given that this has risen for you as
a problem, I'd complete the rest of the exercise NOT using mains line
voltage until you are certain that it does indeed work. Get someone
qualified to check your electrical work.

 

[Adrian C]

Adrian C wrote:
we can
Ah sorry, didn't see that bit. What I suggested would only allow manual
switching to the on state IF the microcontroller had it switched off.

You need a three position switch

Position 1 - off
Position 2 - uProcessor Controlled
Position 3 - on

 

[ehsjr]

Hi,
Please have a look at the circuit at:
http://www.glacialwanderer.com/_blog/blog2008/04_April/hb_relay5.jpg.
It is from the article at http://www.glacialwanderer.com/hobbyrobotics/?p=9.

The circuit it to turn on or off a AC bulb by a microcontroller. My
question is, can we somehow safely add a manual override switch near
the bulb, so that even if the microprocessor is not working, we can
turn the switch on/off manually? If yes, how will the circuit then
look like?
Sorry if this is a simple question as I am just starting in
electronics and electrical circuits.

You can use a single pole, double throw, center off
switch, like this:

o---[YourRelay]---+
AC ----o |
o-----------------+
|
[Bulb]
|
AC-------------------------+

In the off position, the AC is not connected to
either pole of the switch.

Ed