Pages: [1]   Go Down
Author Topic: Digital power switch?  (Read 1256 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 2
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hi,
I'm really new to Arduino, and currently working with a project in which I'm looking for a way to digitally control power supply for an old  television (just on/off).

While the TV obviously demands more power than 5 volts. I figured an easy solution would be something like mounting a "digital" On/Off switch on the power cord that goes into the wall, which i can trigger (on/off) with a digital out pin from Arduino.

Is there such a device? Or am I trying to do this in a stupid way? smiley

Appreciate any help i can get.
Logged

Malaysia
Offline Offline
Sr. Member
****
Karma: 7
Posts: 393
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

a simple way is to use a relay to control the tv on and off. just look for any relay shield would be suffice.
Logged

0
Offline Offline
God Member
*****
Karma: 39
Posts: 988
Get Bitlash: http://bitlash.net
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

There are digitally controlled power switching solutions like this that will keep you safely away from the high voltage, if you are careful: https://www.adafruit.com/products/268

Anything above 5 volts can kill your Arduino, and 110VAC can definitely ruin your day, so do be careful and read up on electrical safety before embarking on any high-voltage work.


-br
Logged

0
Offline Offline
God Member
*****
Karma: 39
Posts: 988
Get Bitlash: http://bitlash.net
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The relay idea will of course work -- it's what's in the product I pointed to -- but I wouldn't recommend running live 110volt AC power on any board to a newbie to electronics.  The cost of small mistakes is too high.  Too much possibility of getting hurt.

-br
 
Logged

Malaysia
Offline Offline
Sr. Member
****
Karma: 7
Posts: 393
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

sorry billroy if my post offended you. At the time of me posting my post i didnt saw your post. and yes is true, i should have not gave any recommendation that could endanger someone.
Logged

0
Offline Offline
God Member
*****
Karma: 39
Posts: 988
Get Bitlash: http://bitlash.net
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

No offense taken, sir.  Your advice was valid but a little incomplete on the safety side smiley-wink

Best regards,

-br
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 2
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hi,
Thank you very much for your help. As you said, I am definitely a beginner at this so i really should really read-up on the possible hazards before doing this.

The powerswitch tail looks easy to use and is a very good tip. (while i probably need a 230v version in that case, I'm living in Europe and we have a 230v electric system.)

After i posted the question, a had another look on the TV (Portable Sony Mega Watchman.) It also has the choice of a 12v DC power in (and i have a 230v->12v Transformer.)


I also found that I own this relay (comes with the sparkfun inventors kit):
https://www.sparkfun.com/products/100?

Does the information provided above mean that it's a more simple thing to do, and would the relay be something i could use for this project? And if so, how would i plug it in? Couldn't find any information on the site.

Again, thanks for the help.

Logged

Malaysia
Offline Offline
Sr. Member
****
Karma: 7
Posts: 393
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I work at Omron that manufacture relay  for almost 2 years. What i can say about a seal relay is that it is a great relay that you actually could use submerge under liquid. if you only have the relay then you need a couple more thing to make it work,
1)a Transistor/Optocoupler would be great
2) a signal Diode,1n4001
3 A power supply that can supply enough volt to activate the relay coil.
wires / board
and last but not least a box preferably a plastic box big enough to contain it all
Logged

0
Offline Offline
God Member
*****
Karma: 39
Posts: 988
Get Bitlash: http://bitlash.net
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

That relay is rated for 5 Amps, which at 12 Volts means it can switch a 60 Watt load (12 x 5) with zero margin.  I'm guessing your TV needs more than 60 Watts, but you can check on the nameplate.  It may even say how much current it needs.  Fortune favors those who operate with safety margins.

So probably not, but a similar relay with a higher current rating would be a good candidate.

Connecting a relay to a digital output pin requires a transistor, a base resistor for the transistor, and a flyback diode.  If you search the forum there are plenty of examples.

-br



Logged

Malaysia
Offline Offline
Sr. Member
****
Karma: 7
Posts: 393
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

dear Billroy i would like to point out that, actually your calculation have some flaw in it. According to the datasheet, It is a 12Vdc relay and it need 37.5mA of current run thru the coil to activate the relay thus closing the contact. ON the Contact part, if the relay is use to power a resistive load, if its an AC circuit ,it can handle 5Amp at 250Vac Max or 5Amp at 30VDC. The total Max Power is 1250 watt for Ac and 150Watt for DC.
Logged

0
Offline Offline
God Member
*****
Karma: 39
Posts: 988
Get Bitlash: http://bitlash.net
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The contacts are rated for 5 Amps.  Exceeding that means you've got no thermal safety margin.  At 12 volts, 5 Amps is 60 watts.

You could squeeze more power through the contacts at a higher voltage, but my understanding is that the load wants 12 volts in this case.

Fortune favors those who design circuits with wide safety margins.

-br
Logged

Malaysia
Offline Offline
Sr. Member
****
Karma: 7
Posts: 393
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Again sorry billray, I miss read the post above, and yeah the contact is rated at 5 Amp. urm maybe what you need is a power relay maybe the kind of relay that i use to make
if you could find a G2R-1-S relay from omron, well that would be great. or the more common would be the MY-2 model.
Logged

United Kingdom
Offline Offline
Tesla Member
***
Karma: 224
Posts: 6619
Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

If I were doing this, I'd consider getting these http://www.maplin.co.uk/remote-controlled-mains-sockets-3-pack-531561 IR-controlled sockets and programming the Arduino to generate the correct IR code for them. But to do that, you need to be able to read IR codes, which requires the right equipment e.g. an oscilloscope and a photodiode.
Logged

Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

Pages: [1]   Go Up
Jump to: