[QUESTION] - Switching 60w 240VAC incandescent via Arduino

Hi there.

I've been asked if I could make something for a local church and their exhibition or something of the sorts - didn't really get much info what it is for at the church, but it's temporary anyway so I'll just leave my Arduino in the enclosure for the time needed. The project requires a 60W Incandescent light bulb to switch on and off at 30second intervals. I've been doing the searches and have found a wonderful post http://www.glacialwanderer.com/hobbyrobotics/?p=9 where the poster does exactly what I want circuit wise, only his is applicable to 120VAC.

The reason I ask is cause I want to make sure it works since it is high voltages.

For my application, I think a electro-mechanical relay will work perfectly fine (30s switching shouldn't be to straining....I think). I found this relay: http://za.rs-online.com/web/p/electromechanical-relays/6168708/

As for the circuit, I pretty much use the one in the blog post over at glacialwanderer.

Am I correct with my deductions for my application, specifically the use of the electro-mechanical relay?

Thank you.

Hello. His blog post looks good. Now I'm gunna basically tell you what you need to do. Your gunna need a light bulb socket. A 120v power cord. A piece of wood to mount the light to. Your Arduino. And probably the hardest part to get is a relay that can handle 120v AC power and has a switching voltage of 5 or less volts. Then you just need to cut your outlet cord in half put one half on one side of the relay the other half on the other. Once you do that attach the end that doesn't have the plug on it to the light blub socket. Next hook one of the outputs on your Arduino to the switch pin on the relay. Once you do that program the blink program to the pin you connected it to. Then screw in the light bulb and plug in the cord turn on your Arduino and it should work!

I'm not a professional at relays but it looks like it should work. You probably wait for someone else to confirm it works before you go and buy it though lol. What does R 20.41 mean. That's the price. What does the R stand for lol. Also you might need to do something with the circuit from the Arduino to the relay besides just a wire so let someone else confirm that to but this is just what I think.

Hi Tecman.

Thanks. As far is needs are, I merely want to confirm the use of that relay since post is 120V and I’ll be using 220V. It looks like it will work but since my electronic and electrical knowledge is very limited, I wanted to check.

Regarding the “R”. Our currency goes by the name “Rand”. So R20.41 is “Twenty Rand and forty one cents”, which is about $2.50.


Arduino seems like overkill for this purpose. A 555 timer could do the trick for the on - off cycling. As for handling the mains, I would use a triac. Cheap and quiet. Here is a similar post: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1266805390

  • Scotty

scottyjr: Arduino seems like overkill for this purpose. A 555 timer could do the trick for the on - off cycling. As for handling the mains, I would use a triac. Cheap and quiet. Here is a similar post: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1266805390

  • Scotty

Thanks Scotty. I don't have any 555 timers nor do I understand them either - I did download a free ebook recently with 555 circuits and hence ordered a batch of 555 chips from ebay - that hasn't arrived yet. I'll look at the triac thanks for the link - I thought of a SSR relay (considering the click from the mechanical relay) but want something cheap, sounds like a drug group...no wait that is Triads. Still :D

EDIT: Wow....555's are cool. Suddenly so many little items I have seen suddenly makes sense - like saying "oooohhhhh! So that will be a 555 application"

Two things to bear in mind with switching incandescent lamps on and off at 30 sec intervals:

  1. When you switch them on, they may take around 14 times more current as an initial surge than in the steady state. A 60W lamp will take 60/240 = 0.25A in the steady state, so the initial surge may be about 3.5A. Halogen lamps have an even bigger surge.

  2. The more often you turn incandescent lamps on, the shorter their life (you may have noticed that lamps most often blow when you turn them on). So your 60W lamp may not last very long.

I would use a zero-crossing SSR to switch the lamp. This will reduce the surge and help prolong lamp life. It can also be driven direct from the Arduino. To further prolong the lamp life, you can connect a NTC thermistor in series with it.


Thank you for the information, much appreciated. As for lamp life, it is not a concern, but cool info non-the-less. I hope to pop round to a local supplier tomorrow....work is keeping me way to busy. :(

Did you try searching for information? There was this thread, right in this forum, about a week ago. http://arduino.cc/forum/index.php/topic,92164.0.html


Actually I did...but my combination of search words didn't yield results - looking at the heading of the link you posted, it now makes sense to search in that combination - I searched "relay to switch 240VAC" and combinations there-off - I think putting in lamp gets better results. Thank you for the link.

I'll pop round to a local supplier hopefully today and just find out which electro-mechanical relay will work - I'm not looking for the best solution, just a workable solution for a short period of time. Looking at that controller board, I was also thinking of designing a board for this type of application for future use, now I don't have to. :D

... and just find out which electro-mechanical relay will work

I think a solid state relay would be a better solution. You can generally drive them directly from the output of your Arduino and they incorporate the zero crossing switching technique. Don't hesitate to grab a used one, they are virtually indestructible if they aren't abused. I have some that I picked up at a hamfest that have been running my baseboard heaters for more than 30 years.


EDIT: I thought that comment in your signature looked familiar ....

@ floresta.

Thanks. Only thing in South Africa, or at least in Port Elizabeth (my town) finding used electronic equipment is incredibly hard to find, unless you are working within a related field.

I will find out from a local supplier what they have available in SSR, hopefully not to expensive. Given I might do the project with a 555 there might be a bit more le-way in terms of input voltage. Since everyone says SSR, I will go see how much they cost locally - given I can reuse them in the future it will probably work out cheaper in the long run.

I love that comment you made, hence in my signature. Made me laugh then, makes me laugh now when I think about it. Persistence and a lack of rules does wonders for success.

Thanks floresta.....and everyone else...I catch the drift! GO SSR!