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Registered Member #7669
Joined: Mon Oct 29 2012, 02:55PM
Location:
Posts: 19
Hi
I hope somebody can help, I have a bit of a conundrum.
I am making an electronic mechanism for a bar billiards table. It is battery operated, controlled by an arduino. You press a button and the bar is lifted by a servo to let the balls out. After 15 minutes the bar is lowered by the servo.
The problem is, since it's run off a battery I don't want the arduino to be powered all the time otherwise the battery will quickly run out. I was hoping that I could hold the button for a second which would trigger a solid state relay to supply power to the arduino. Once the arduino is booted then one of the outputs (attached to the relay coil) could stay on, keeping the relay switched after the button is released. Once the bar has been lowered then that output would switch off, cutting power to the whole thing.
Would that work? Has anybody tried something like this before?
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
What you are looking for is called "power gating" and you can look up the best ways to do it.
I cannot follow your schematic so I'm inclined to say it's wrong. You should have the relay and pushbutton in parallel, not series, I think, for what you aim to achieve.
Alternatively, you can use a chip with a low-power mode that can be turned on by interrupt via pushbutton. Since there is very little computational complexity in carrying out what you describe, something basic like TI's MSP430 value line comes to mind.
Registered Member #7669
Joined: Mon Oct 29 2012, 02:55PM
Location:
Posts: 19
Thanks for the help, I already have arduino chips so was hoping to use them if possible.
I have added labels and colour coded the diagram to hopefully make it clearer what's happening, don't worry if you still can't make sense of it though.
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
Okay that should work, but you'll either have to make sure that D8 can NEVER go LOW (it will short the supply when the button is pushed) or put a resistor at D8 to protect against shorting the supply.
EDIT: said "high" replaced with "LOW"
SECOND EDIT: A better solution may be to disconnect the bottom end of your pushbutton as shown in the picture and connect it to Vin on the chip directly. That way, the button will still turn the chip on and the supply will not be directly connected to the chip's output pin.
Registered Member #1565
Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159
GIven you use a AVR8, they do brag about the sleep modes. So if you keep the microcontroller powered at all time (but in deep sleep mode), and connect the button to one of the int-pins (pullup, and switch toward gnd). You will only need to add a microcontroller-controlled FET to cut servo-power for power-down.
Given the power-source is 3-5.5V without regulators.
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
If i were you i would just use two buttons! Start and stop. Google "seal in circuit". If you put the circuit between the battery and the other parts of your circuit it will only be on when you push the start button. When you hit stop power will be cutoff. Simple but very common!
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Relay - Self Energise?
