I've searched a bit here, for example https://electronics.stackexchange.com/search?q=pulse+switch, but I haven't quite found what I'm looking for.
Here's the actual problem: I want to send a signal to a server, wirelessly, every time a door is closed (it would be fine to send on open and close, but all I need is on close). I'm open to other solutions, but my current approach (using materials I already have) is to use the Amazon dash button hack (https://medium.com/@edwardbenson/how-i-hacked-amazon-s-5-wifi-button-to-track-baby-data-794214b0bdd8 for example), along with a reed switch. This means I need the dash button to be momentarily pressed when the door state changes – that is, if the door open/closed state is represented as a 0/1 signal, I want a circuit that generates a short pulse when that signal goes high.
I know this can be done with an XOR gate and RC, I think I can do it with three NAND gates, and I'm sure there are a few other simple powered circuits that can do this. The problem is the dash button runs on a single 1.5V battery, so I'd like to do it either passively, or with a power draw that does not significantly effect the battery life. It seems to me that using CMOS logic to do this would work, but 1) I'm not sure how well it would work at 1.5V, and 2) I'm wondering if I'm missing a simpler or better solution. So…
The question I'm trying to ask: What is the simplest/cheapest/lowest-power way to generate a short pulse, in response to a door changing state from open to closed? Ideally, passively, with a reed switch.
The question that might be better answered: What is the simplest/cheapest/lowest-power way to send a boolean signal, wirelessly, to a web server in response to an edge in the door state?
Best Answer
Mount the reed switch on the outside of the door jamb, and the magnet not opposite the switch on the door but on the other side horizontally.
That way the switch is not closed while at rest, but briefly closes every time the door goes past.