$3 USB volt/ampere meter

[lpc32]

The MCU is Holtek HT46R064B.

What's that component to the right, next to the filter cap and the resistor? Looks like there's something metallic protruding from the top of it (see full size image). Not sure if it's from the inside, after the poor thing's been mutilated with heat, or if it's something that's dropped on it.

Any idea why only the MCU is reflow soldered? (Or maybe it's done manually by someone else.)

There are red spots under the components, I assume to glue them while soldering. Is that standard practice of some sort?

What's the 0.5ohm resistor for?

[8086]

What's that component to the right, next to the filter cap and the resistor? Looks like there's something metallic protruding from the top of it (see full size image). Not sure if it's from the inside, after the poor thing's been mutilated with heat, or if it's something that's dropped on it.

Probably a diode. I can't see the protrusion you're talking about.

Any idea why only the MCU is reflow soldered? (Or maybe it's done manually by someone else.)

Doesn't look reflowed to me. Probably drag soldered.

There are red spots under the components, I assume to glue them while soldering. Is that standard practice of some sort?

Yeah, that's glue. Not sure why it's been used in this case, maybe they prefer to have someone glue the component and then pass it to someone else for soldering...

What's the 0.5ohm resistor for?

Current sense presumably.

[lpc32]

Probably a diode. I can't see the protrusion you're talking about.

The grey round dot near the top of the component (visible in the full image). Difficult to see what it is without an angled shot (bad light, all turned out blurry), but it definitely feels protruding.

What's the 0.5ohm resistor for?

Current sense presumably.

It's on the USB shield.

[Balaur]

What's the 0.5ohm resistor for?

Current sense presumably.

It's on the USB shield.

It's on the GND path from input to output (low-side current sensing). This way, the MCU only has to measure a low analog voltage with one pin, as opposed to two pins needed for a sense resistor on the VDD, or a differential amplifier. The ADC's resolution could be also better.

[8086]

Probably a diode. I can't see the protrusion you're talking about.

The grey round dot near the top of the component (visible in the full image). Difficult to see what it is without an angled shot (bad light, all turned out blurry), but it definitely feels protruding.

Probably a stray bit of flux, or glue, or something. I don't think it's meant to be there.

What's the 0.5ohm resistor for?

Current sense presumably.

It's on the USB shield.

Low side current sensing, is easier to implement as Balaur said already.

[lpc32]

Oh, because the shield's also connected to the GND. Thanks. Why better resolution?

Whatever it is on the diode definitely wasn't supposed to be there, but it does look very much like something metallic coming out from the inside of the distorted package. Oh well.

[SeanB]

Current measuring has only a limited range as the voltage drop it has must be low so the USB device plugged in still has a power rail within the USB spec. So most of the ADC range is not usable as you only use the very lowest bits, the rest being unusable. Thus you might have 10mV resolution on volts, but the current will only have 10mA at best, and you will only have about 300 counts for current, while voltage will have 350 at a point where the ADC is less noisy as it is near the top of it's range.

Still they do work well enough, I bought 2 and they agree within 2 counts on voltage and 1 count on current. The mystery component is a diode, marked on my one as RA and with IV at right angles on the end. No idea what diode, but it still is readable. According to the one they draw around 10mA to 20mA depending on what is displayed.

[AmmoJammo]

surface mount components get stuck on with glue, then the board is through hole loaded, and put through the wave soldering machine, which solders the through hole, and the surface mount stuff that's hanging off the bottom of the board

[zapta]

I am using one of those and it's very useful to optimize charging speed. Some charger/cable combinations give higher charging currents than others.

Sent from my Nexus 5 using Tapatalk

[zapta]

What's the 0.5ohm resistor for?

0.5 ohm sounds too high, will cause a 0.5V drop at 1A. More likely 0.05 ohm.  Measure the voltage over it while charging and use the displayed current and ohm low to compute the resistance.

[zapta]

Hey OP, thanks for pointing this out, I ordered one!

Do we need a "useful Chinese gadgets" thread?

Good idea. Here is a recent example https://www.eevblog.com/forum/reviews/another-helping-hand/msg0/#new . I would add the Bakku pcb holder http://www.dx.com/p/baiku-bk-687-stainless-steel-repairing-pcb-holder-for-cellphone-silver-284069#.U2j9LK1dUog

[Stonent]

I think the person who did the soldering was having a fit of sneezing while doing it. 

[zapta]

I think the person who did the soldering was having a fit of sneezing while doing it. 

And I thought this was flux ,..

[lpc32]

Ammo: I guess they just seriously miscalibrated their thermal profile. (And their pick-and-place broke in the middle.)

zapta: Right. I skipped the R.

[lu33390]

hello , an hand draw schema from france ... the componant to the right is a 2v5 regulator like TL431 , code RA (I do'nt find any .pdf on it) , is Q1 on my schema .

[Rick Law]

What's the 0.5ohm resistor for?

0.5 ohm sounds too high, will cause a 0.5V drop at 1A. More likely 0.05 ohm.  Measure the voltage over it while charging and use the displayed current and ohm low to compute the resistance.

The photo shows R050 = 0.05 ohm.

[aargee]

What I find funny is that the silkscreen is all mirror imaged.