Touchscreen goes haywire when plugged in to charger

[Robby368]

I've had my RAZR M for two days now, everything is awesome except...

At work I'm able to have my phone plugged in to the charger when the batt starts getting low. Today when I plugged it in and tried to send a text message, the touch screen was rendered useless. It was hitting all over the place, usually nowhere near where I touched, also couldn't use other apps and games because the touchscreen wasn't working right.

I unplugged it from the charger and it worked flawlessly.

What would cause the touchscreen to go haywire when the phone is plugged in to the charger???

 

[Bratster2]

Usually that means it is a poor quality charger.

Are you using the one that came with it or an aftermarket one?

 

[FoxKat]

Bratster2 is correct. The touchscreen is a capacitive touch-sensitive screen which in fact doesn't actually need to be touched. If you put your finger close enough, it will still register. Samsung took that a step further and enhanced the sensitivity so that you can actually wave your hand over, or dangle a finger over the screen to move objects, select and even preview.

All that sensitivity comes at a price. Just like old-time radios where as you walked near by the signal got crappy for a sec, the same thing happens in these screens and that's essentially how it knows where your finger is. It senses a change in the capacitance (voltage difference across an open pair of contacts), at a junction etched or otherwise printed on the digitizer as a circuit of hundreds of intersections - each with a capacitor and other solid state circuitry at the junctions. When your finger or other "conductive" materials come close, it changes the capacitance at a group of those junctions and the circuit maps out that group to determine where your finger is. In order to detect the change in capacitance, it is using very minute changes and amplifies them to levels in voltage many times the ambient (background) voltages, so it can differentiate between background interference such as nearby wires, radio transmissions, motors or electronic devices and the actual finger.

In order to be so sensitive it has to have a very pure source of power. Batteries are the absolute best because the power they send out is very clean - free of any type of variations or "ripple" or other RF interference. It's comparable to the difference between a calm lake with no wind where the water looks like a giant flat mirror, and that of a stormy body of water with lots of ripples and splashing about. Unfortunately when you plug in a charger, and if it is not a very highly filtered power source it can impart fluctuations in the voltages coming from the AC power source at the wall outlet (as well as other interference it can pick up from the air and nearby such as electric motor noise, TV yoke and other electromagnet RFI, portable phones, garage door openers, radio and TV transmissions and a myriad of other transmitters), and that "dirty power" can find its way into the circuit which is trying to differentiate your finger from the noise. As you've witnessed, the noise can be too "loud" and drown out the desired finger-press detection. Disconnect the power adapter and the problem instantly goes away.

To avoid this, first and most importantly ALWAYS use the wall adapter supplied by the manufacturer if at all possible. If that Original Equipment Manufacturer (OEM), adapter isn't available try to stick with top name brand cell phone adapters rather than aftermarket third party manufactured adapters. Second, ALWAYS use the cable supplied by the OEM as well. These are highly shielded cables designed to reflect away from the wires inside any RF interference so it doesn't jump on board and take the ride into your phone.

Trust me, I've taken lots of these adapters apart and they vary widely in the number and type of components - the level of technology used to convert the dirty 110AC (Alternating Current), power to a clean and highly filtered smooth and stable DC (Direct Current), power source. I've found that most of the aftermarket devices use a very simple bridge rectifier circuit with some capacitors to try and "filter" out the AC ripple, but they're poor at best. Then they're inside a plastic case with no RF shielding and the wires they use to send that dirty power to the phone's USB jack are often not even shielded twisted pairs but instead are un-shielded straight pair wires. In other words, these devices are essentially giant antennas pulling in all sorts of RF interference to add to the already dirty quasi-DC power. It's a wonder the phone can even function with it.

By contrast the OEM charger adapters are usually containing a very complicated circuit board with at least one, if not several integrated circuits, along with plenty of other filtering and tempering components all designed to give your phone the cleanest drink of power it can get. This clean power will allow the phone to continue to operate at or near the same level of sensitivity as with the battery and likely work fine while charging.

I always say, in most cases you get what you pay for. It's an old saying and yeah...I sound like your grandfather, but seems exceptionally accurate when pertaining to technology. It only makes sense...if the stock charger costs $29.99 retail and the aftermarket one costs $5.99, odds are there's comparable profit for both but dramatically lower cost to manufacture for the cheapo.