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

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Trevor Rymell

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Apologies if this is not in the correct section of the forum to post this.

I recently bought a cheap and cheerful digital microscope for electronics work. The exact model is Andonstar AD208S as shown in the image. However, I'm not expecting anyone to have detailed circuit knowledge of this 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
 

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I would imagine that it's working as designed? - just plug it in, then turn it OFF with the on/off switch on the front.
 
Thanks, Nigel. You may be right but I'd have expected to be able to just plug in into the wall then switch it on or off using the button provided just like any TV or PC or the dozens of other devices we all use. As you say, I can just live with it.

Interestingly, this manufacturer sells (as an optional extra) a IR remote which controls almost all the functions but has NO on/off button. The first time I've ever come across that. I suppose they cut a few corners to keep the cost down.
 
Some devices do this so they recover after a power cut. Does it have some kind of automated recording function? If you'd set it up to do time-lapse and a 1 second power-cut stopped it I think you wouldn't be pleased.

Mike.
 
Hi Mike. Yes, I've seen my PCs do this a lot but I don't think this device is as sophisticated as that. It's nothing more than a 2MP camera with an LCD screen attached. Works great as a microscope and PCB inspection tool.
 
Thanks for the reply. My experience differs from yours. None of the many dozens of consumer devices I've owned over the years ever did this. If there's an On/Off button, that's how it turns on after being plugged into the mains.

In the case of TVs, VCRs, DVD players and the TV set top box I got from my ISP, the RTC displays will light up when plugged in but I still have to press the On button on the machine (or the IR remote) to bring them out of standby mode and operate them.
 
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I've seen lots of devices that have mechanical latches in the on-off buttons or simply on-off toggle switches. They will just power up or not depending on the state of the switch.

For unattended items, like routers or fridges, having an on-off button that needs to be pressed after a power cut is a real pain.

For stuff like power tools, or cooker hobs it's really not a good idea to have them power up without the button being pressed.

In the case of the microscope, it's really not that important either way.

Are you sure that it's not just remembering how it was last left, in the same way that a mechanical switch would?
 

Diver300
Thanks. It's a normal push-to-make PCB mounted button as you find on 90% of consumer devices, PC's etc. I agree it's not that important. I was just wondering if I could do anything about it. It seems a bit curious to install a power button that can only be used to power ON the device AFTER it's already been powered up and then switched off once.
 

It seems perfectly normal? - and is the default action of Philips Hue bulbs.
 
The timing of this thread is funny because I was just asked to modify a device that does not turn on when plugged in (even if the toggle switch is turned to "on" when plugged in. The owner wants to connect to a an outlet with a wall switch and have I turn on with the wall switch. This is easy, with a cap, a large transistor and a PNP transistor. The toggle switch already had a pull-down resistor. Just bypassing the toggle with the PNP - the cap and big resistor give me a 3-second delay required for the microcontroller to be ready for a switch event.
 
Hi Gophert
So the toggle switch must be in the "Off" position or it will not turn on when plugged in, is that right? I've not come across that before. I wonder why the designer used a toggle switch in that case.

What is also interesting is what different folks think is "normal" behaviour for the class of device I'm using. I've never used a single consumer product equipped with an On/Off button (and I've owned very many over the years - TVs, VCRs, DVD players, short wave radios, PCs, set top TV boxes, Hi-Fi receivers etc) that behaved the way this one does. Not a single one powered up (as opposed to just entering standby mode) as soon as plugged into the mains.

What I think of as normal is you plug the thing into the wall, the standby light or clock/counter display (if there is one) lights up but then you have to press the On/Off button on the front panel or remote to operate it. The only exceptions will be devices with no On/Off switch in the first place.

To me, the way this device behaves suggests sloppy design rather than a fault but as I've said, it's no big deal and I can live with it. I posted here in case someone could suggest an easy mod I could carry out to make the device wait till the On/Off button is pressed like all my other devices do. The best suggestion I've had so far (courtesy MacintoshCZ) is simply add a line switch to the USB cable which would certainly be easy.

Thanks for the chat
Trevor
 

You mean like almost every modern product

The product in question, like almost everything else, doesn't have an on/off switch, it only has a standby switch
 
Hi Nigel
You're correct. The button is often labelled "standby" but just as often "power" or not labelled at all as in this case but no device I've ever owned (till now) starts working as soon as it's plugged into the mains. In all other cases, I have to press that button before I can watch TV or play a DVD or start using a PC or whatever.

This device in question has what looks like the usual power/standby button (unlabelled) but the machine will have already switched on (ie the LCD screen starts displaying an image) as soon as it's plugged into the mains. The standby/power button can be used AFTER that to switch the device OFF and then ON again and this appears to be how it was designed.

In my experience, it's an unusual way to implement a standby/power button and would have preferred to have it behave like everything else I own ie not start displaying an image until the button is pressed AFTER shoving the mains plug in. Still, I guess it's just academic at this point.
Thanks for the input
Trevor
 

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