I need to "design" a on/off switch for main (230V), and it need to be covered with a printed "keyboard" film.
For safety I want to avoid using a IO from tha AVR (if it lock up you can't turn the thing off)
I have found a microswitch for 230V (for PCB mount), but not one that is latched are there any?
I could make it with two switches (a make and a break one).
If I have make it with a NO (make switch), are there a simple way to make it turn a relay on if off and off if on ?
(not to big :) )
Can't say I've ever seen a latching snap-action ("micro") switch.
You could use a latching relay and two normal microswitches, though, if you want it to be all mechanical.
I have found a microswitch for 230V (for PCB mount), but not one that is latched are there any?
I could make it with two switches (a make and a break one).
http://www.reuk.co.uk/Latching-Relay-Circuit.htm
If I have make it with a NO (make switch), are there a simple way to make it turn a relay on if off and off if on ?
555 AS A FLIP FLOP
A 555 contains a flip flop along with a couple of comparators. When the output at pin 3 is 'high', C1 slowly charges through R1 up to 12V; when it is 'low' C1 discharges through R1 down to 0V. Pressing switch S1 upsets the 6v balance between R2 and R3 on pins 2 & 6 for a split second, triggering the flip flop and changing the state of the output from 'high' to 'low' or vice-versa. The wide hysteresis of the 555 (between 1/3 supply voltage and 2/3 supply voltage) limits false switching from switch bounce.
You'll need a 12V (or other low voltage DC) source, but then you just drive a relay coil to switch the 230 VAC.
Though not immune to electrical noise and other disturbances, the 555 is a darned sight more stable than an MCU in adverse conditions. I would steer clear of any low-power CMOS versions of the 555 for this application. I don't know if it is susceptible to latchup in the same way that CMOS logic is, but since you'll be driving a relay anyway and a 230 VAC load you probably don't need to worry about saving a few mA.
You can of course just use a normal flip-flop like the CD4013 (or TTL equivalent... 74LS74?) . That approach, as well as the 555 approach above, a discrete component flip flop, and one that uses a single button with three relays (with some limitations), are seen here:
http://www.pcsilencioso.com/cpem...
The 3-relay 1-button solution is clever, but probably not the best for your app. The relays must all be driven at the load's voltage, meaning the NO button would need to pass 230 VAC. You could add a 4th relay with a lower coil voltage for safety.
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It is a solution like the Ne555 timer, but at 230V. The problem is that I want to have power 100% off when turned off. When it is on I have all the 5V and 12V I need.
So the on key need to be 250V, but the self lock relay can be with a 5V coil. (it could be made with the AVR, but if it lock up you can't turn it off, and that is not safe. )
Then maybe the three-relay solution is the best for you.
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"Experience is what enables you to recognise a mistake the second time you make it." "Good judgement comes from experience. Experience comes from bad judgement." "Wisdom is always wont to arrive late, and to be a little approximate on first possession." "When you hear hoofbeats, think horses, not unicorns." "Fast. Cheap. Good. Pick two." "We see a lot of arses on handlebars around here." - [J Ekdahl] |
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