Wednesday, May 19, 2010

So what did you learn in school?

I recently bought a 44780-based 16x2 LCD module from a shop I frequent. Before handing over the LCD they test it to show their client that it's in working order. To perform the test they have this inhouse device which I was later told is based on a Zilog MCU. The LCD module is simply plugged in, the unit switched on, and characters appear on the screen.

Just my luck. The test jig wasn't working. So the saleslady called in a technician. He brought out an analog multimeter and after probing several points on the PCB concluded that the linear voltage regulator (he pointed to a TO-92 component) was busted. He asked the saleslady how much the output of the AC adapter was. She said 9-volts, 1 ampere. He replied that was too much for the regulator which could only take 500mA. That must be what caused it to burn out.

At that point I couldn't help but chime in. I told the guy in a way as not to sound confrontative that rather than the adapter, it's the load that determines whether the current limit of the regulator is exceeded or not. He didn't listen and remained pretty convinced he was right. He asked his colleague for a regulator in a TO-220 package, because his reasoning is that a component that has a 1 amp (or 1.5A) rating will be able to handle the 1 amp current being supplied by the adapter. I certainly wasn't going to argue and give him an EE101, although in my mind I was already lecturing him on how you could hook up a 12-volt car battery that can deliver 50Amps or a 24-volt truck battery that can pump out even more current and the tiny voltage regulator chip simply wouldn't mind. At that point I just took a seat, got my phone out of my pocket and texted people. Minutes later--many minutes later--when he finally got the device working I found out from him that the regulator was just fine. Instead it was the jack into which the AC adapter is plugged into that was on the blink.

State of electronics education leaves much to be desired. I do consider knowledge of the nature of  the voltage regulator's current rating pretty basic. Confusing what it refers to is an egregious error.

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