tastewar wrote:Certainly, the tact switch alone is cheap, but adding in the other components, the board, the assembly time or cost, do you really come out ahead on cost?
Yep. For the ones I make, the total parts cost is about 20c.
tastewar wrote:Agreed! Very cute & clever (I'm sure; certainly beyond what I could do). I'm still left wondering -- does it do more than a push-on/push-off? Is it debounced, or does it handle more current, or ???
Yes, this circuit does debounce the switch. The power from this circuit will have the nice, glitch-free on/off transitions that are important for getting logic circuits to start in a known state. To get equally good transitions from a slide switch or latching pushbutton, you'd have to follow it with a debounce circuit that contains almost as many components, with their associated board space and assembly costs.
As power goes, you could use this to drive a few 40A power mosfets if you wanted to, but that's kind of a red herring.. you could drive the mosfets with a mechanical latch as well.
The big advantage of the general circuit is that it turns the circuit's power state into a signal you can control electronically. You could use this to power a 555 timer with a 5-minute delay, then have the 555 send U1A's output HIGH, killing the power. The result is an auto-off function that would be hard to implement with a slider or latching pushbutton. You can connect a diode to the top of C1 and get an enable/disable feature that keeps the circuit from turning on or off until some external condition is met.. again, hard to do with a mechanical latch. You can wire multiple switches in parallel and control the circuit from several different places.
And yes, in this instance, there's fair bit of "whoa, cool!" factor. ;-)
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