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.

 

[Rheilly Phoull]

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.

Wire a switch across the collector to ground.

R.P

 

[saurabh9]

Wire a switch across the collector to ground.

R.P

Thanks for your response,
Will that ensure that if the bulb was turned on by the microprocessor,
then
i can manually turn it off and vice versa?

 

[Jasen Betts]

Thanks for your response,
Will that ensure that if the bulb was turned on by the microprocessor,
then
i can manually turn it off and vice versa?

no with the switch wired like that to turn off the bulb you'd have to cut the 5v power.


otherwise you need a three way switch.
cut the wire to the collector

arrange it so the one position has the that connection broken - (this is override off)
another has that connection made (this is microcontroller control)
and the third has the relay connected to ground (this is override on )
the third position can have the cut connection either made or broken

another option (if you have an on-off-on switch and want the middle
position to be microcontroller control) is to have one of the on's
ground the base and the other ground the collector.

Bye.
Jasen

 

[ian field]

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.

It can be done the same way as a normal 2 way lightswitch.

You need a single pole changeover relay unit controlled by the micro, the
common contact is fed by supply and the 2 other contacts feed a pair of
wires between the relay and your manual switch. The manual switch of course
picks off whichever of the 2 wires happens to be live to turn on the light -
the manual switch is of course also a single pole changeover with the common
terminal to the lamp.

 

[JeffM]

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 you feel you MUST post the *same* question to MULTIPLE groups,
DON'T do this
http://groups.google.com/groups/sea...ZiC4SlockX83b8rhlH0Pnl47z4AZhN98BFg&scoring=d

Do this instead
http://www.google.com/search?q=cach...arked-as-Read-in-ALL-*-groups+Newsgroups.line

Your question could have easily been answered in this one group
and there was NO reason to MULTI-POST it.

 

[saurabh9]

If you feel you MUST post the *same* question to MULTIPLE groups,
DON'T do thishttp://groups.google.com/groups/search?q=two-way-switch&enc_author=7b...

Do this insteadhttp://www.google.com/search?q=cache:qHhBKJ-sXKYJ:en.wikipedia.org/wi...

Your question could have easily been answered in this one group
and there was NO reason to MULTI-POST it.

Sorry Jeff and others for the cross posting. These being my first
posts to these groups, I was not sure which group would answer the
query better. Will keep in mind in future. And thanks for the help
everybody!

 

[theamber]

You just need to put a SPST switch across the relay contacts. If the SPST is on your aurdino wont be able to control it anymore untill you turn the switch off manually.
Your original questions was in case the Aurdino stop working so they you have it.

 

[Jamie]

Thanks for your response,
Will that ensure that if the bulb was turned on by the microprocessor,
then
i can manually turn it off and vice versa?

You need a 3 way operation for that.

Your micro needs to drive a DT (double throw) relay), the manual
switch also needs to be a double throw switch which is a common stock
item at your local electrical supplier for lights.

Lets assume the relay's CP (Center Pole) is connected to 120 volts AC>
and the CP of the switch is connected to the L1 (High side) of the Lamp.
Then you simply combined the poles of the switch to the poles of the
Relay..

As long as 120 V is at the CP of the relay, it will not matter if the
processor is working or if it happens to have the relay already pulled
in. The manual switch will simply place the lamp in a opposite operation.

You can go one step further by making the circuit a 4 way and up!
all that simply involves doing is taking the 2 leads that are being used
to bridge the poles together between the relay and switch, and pass them
through a DPDT (double Pole, double throw) switch to reverse/flip the
leads orientation between the relay and manual switch..
In fact, you can have as many of these DPDT switches you want
between the relay and manual switch..

http://webpages.charter.net/jamie_5"