things said:
how about a latching relay, i don't think they use power once they have latched so all you would have to do is get a simple circuit to send pulses to a relay when the signal is recieved.
things,
That sounds great, and would remove many of the design problems!
One such relay, for which I found a datasheet at mouser.com by searching for "latching relay 5vdc", says it needs a minimum pulse width of 10 ms. So it seems like maybe he could just let the pulse width be controlled by how long he holds down the button on the remote, unless that might be able to waste too much power, e.g. if the button was accidentally held down for a long time, or maybe even in comparison to having a circuit at the receiver that would just produce a short pulse of 20ms or so, no matter how long the button was held down, rather than a typical button press length of maybe 0.5 sec. With one relay I found, it would use about 100mW for however long the pulse was, each time (see below). He would have to decide if it was worth adding the pulse-length-control circuitry, to save that power.
The relay I happened to look at, which was just the first 5V latching one that came up and may not be the best one for this application, was an OMRON G6JU-series surface-mount type, and has a 10mm x 5.7mm footprint, and a height of 10mm. It can carry up to 1A of current. The coil triggers at >= 75% of 5V (i.e. 3.75V or more), for both Set and Reset, and has a resistance of 245.5 Ohms and a rated current of 20.4 mA. So power consumption when pulsed would be about 100mW.
There are also similar relays that work on 3V instead of 5V, although they use about the same amount of power, when pulsed. And there are through-hole versions for most of them, too.
It might be better to use a relay with a 3V coil, because it could work even for lower (partially-depleted) battery voltage levels, and would make the coil-driver circuitry easier to design, by giving more headroom if the available supply voltage was only 5v, for example.
So, with a latching relay like the 5V one I mentioned (modify the following if a 3V relay is used), it seems like at the receiver end he'd only need a way to produce 4V to 5V quasi-DC that could push at least 21mA, whenever the receiver got a signal from the transmitter, and 0v (or even up to 3V or so) when no signal was present (and maybe limit the pulse length, if desired, as mentioned above). There are probably at least several different ways to do that. But it would probably mostly depend on exactly what types of transmitter and receiver were used.
- Tom Gootee
**broken link removed**
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