Pages: [1]   Go Down
Author Topic: Auto shut down AC Power  (Read 945 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 12
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hi,

I would like to build a device with a power button, the device will be plugged into AC outlet. I would like to be able to switch off the device after some time. I understand how to do that if I power my board from a battery. But it almost seems that I would have to have some part of my circuit always powered to check the state of the power button in AC case. Does anybody know if there is a push button that makes a connection for AC, but also has an additional pin that will break the connection if set?

I would like to have this switch before the AC power goes into an adapter to power up my board. Is this feasible?

Thanks,
Alexander
Logged

Left Coast, CA (USA)
Offline Offline
Brattain Member
*****
Karma: 361
Posts: 17263
Measurement changes behavior
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Keep it simple, something like this should work:

http://c773974.r74.cf2.rackcdn.com/0381251_153700.jpg

Lefty
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 12
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I would like to switch my device off after some time, so I do not have to do it manually. But if I can not find a reasonable solution I will go with a simple solution smiley
Logged

Left Coast, CA (USA)
Offline Offline
Brattain Member
*****
Karma: 361
Posts: 17263
Measurement changes behavior
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I would like to switch my device off after some time, so I do not have to do it manually. But if I can not find a reasonable solution I will go with a simple solution smiley

Ok, how about this?

http://1.bp.blogspot.com/_f2TjoRrM27k/TD12YBkV2aI/AAAAAAAAAeQ/HZV8ehjlWk4/s1600/timer-switch.jpg

Lefty
Logged

United Kingdom
Offline Offline
Tesla Member
***
Karma: 224
Posts: 6593
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 you want to control the switch off from a microcontroller, simplest approach is to use an AC mains push button. Bypass the button with an SSR controlled by the microcontroller.

Alternatively, leave the device powered from the mains, but use a power supply with low standby power consumption. For example, here http://proto-pic.co.uk/usb-power-supply-adaptor-uk-plug-1-2a/ is a 5V 1.2A power supply with a standby power consumption of just 0.17W. You don't need to power the microcontroller off, just put it in power down sleep mode.
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.

Offline Offline
Newbie
*
Karma: 0
Posts: 12
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

That would work, but I want microcontroller to determine what the timer delay is.
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 12
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

If you want to control the switch off from a microcontroller, simplest approach is to use an AC mains push button. Bypass the button with an SSR controlled by the microcontroller.
Could you elaborate? I have a push button and SSR in parallel. Push button does not preserve the state, right? AC will flow as long as the button is pressed. Let's assume the device is not powered and SSR is off.  So while AC is on (when I pressed the push button) I need to flip SSR so it allows AC as well. This means that I need something that works only when SSR is off, but the power is on. And then I need something to detect the press when the device is powered to unpower it.

This seems like something I should not be inventing. I know my Keurig coffee maker has this functionality (my wife will not forgive me if I take it apart smiley ).
Logged

United Kingdom
Offline Offline
Tesla Member
***
Karma: 224
Posts: 6593
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

OK, so you want the same push button to serve as an off-switch as well as an on-switch. In that case I think it would be better to keep the device permanently powered using a low-standby-power PSU. That's probably what your coffee maker does.
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.

Offline Offline
Newbie
*
Karma: 0
Posts: 12
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

OK, so you want the same push button to serve as an off-switch as well as an on-switch. In that case I think it would be better to keep the device permanently powered using a low-standby-power PSU. That's probably what your coffee maker does.
I see. It seems that I can have my cake if I put more logic (as well as power adapter) on the branch with the push button. Thanks for the input.
Logged

Pages: [1]   Go Up
Jump to: