Really Basic Power On Question

Started by February 16, 2021
```This must be a really really common problem and the only reason it is diffi=
cult to find on youtube is the wrong search terms:

If a device has a power on button latch switch and you want it to turn on a=
nd off like a light bulb, i. e., when the power supply is plugged in or a r=
elay connects the power, or for solar, when the sun comes up, is it a commo=
n solution to run a wire from the power supply through a cap and maybe a la=
rge drain resister in parallel then to one side of the latch switch?

The current would flow through the cap just long enough to set the latch sw=
itch before the cap is charged and stops the flow.

Then the device turns on and stays on until power is disconnected.  The pro=
cess can repeat after the charge drains off the cap.

First check the voltage through the on switch is the same as the power supp=
ly.  (This will not werk on a lap top.)

I'd need some idea of the time it takes to latch and some thresh hold volta=
ge for the latch to select the cap and resister.  Maybe look at it on an os=
cilloscope.

```
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Bret Cahill wrote:
> This must be a really really common problem and the only reason it is
> difficult to find on youtube is the wrong search terms:
>
>
> If a device has a power on button latch switch and you want it to turn
> on and off like a light bulb, i. e., when the power supply is plugged
> in or a relay connects the power, or for solar, when the sun comes up,
> is it a common solution to run a wire from the power supply through a
> cap and maybe a large drain resister in parallel then to one side of
> the latch switch?

don't follow your description here at all. Are you just trying to
figure out a "simple" way to pulse a latching relay's coil long enough
for it to set?

Note that in order to reset a latching relay, one normally needs to
drive a secondary coil, or reverse the current flow in a single coil
model; so if I'm understanding your question properly, you're never
actually going to "unlatch" the relay.

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