Device powers up as soon as it's plugged into the wall.

[sacentre]

I recently bought a cheap and cheerful digital microscope for electronics work. The exact model is Andonstar AD208S. However, I'm not expecting anyone to have detailed circuit knowledge of this particular device. I'm just hoping for some general advice.

The unit is powered via a 5v micro USB cable and I'm running it off a generic mobile phone charger. The unit has an On/Off button on the front.

The problem is the unit powers up as soon as the charger is plugged into the wall or when the mains switch on the wall the socket is switched on. It powers down normally using the On/Off button on the front.

I tried half a dozen different chargers which made no difference so I'm assuming this is a problem with poor internal power supply design or smoothing in the unit itself. It's no big deal keeping it unplugged till I need it but it would be nice to be able to switch it On using the button on the unit itself.

I was wondering if there was a simple fix I could try such as soldering a cap across the 5v rail or something like that (I'm guessing).

Thanks in advance.
Trevor

 

[Martaine2005]

My unit does the same. In fact both of my different units power on when USB is connected.
One of mine has an internal rechargeable battery.
I just use the on/off button after connecting it to turn it off. Then the on/off button works just fine when I want to use it later. Hasn’t been a problem or even something I thought about.

Martin

 

[sacentre]

Thanks, Martin. Good to know it's normal behaviour. I agree it's not really a problem. I just wondered if there was a way to make the unit stay off the first time until the power button was pressed. I suppose I can always add a small switch somewhere but probably won't bother.