$3 USB volt/ampere meter   - Page 1
Forum section: electronics / general

author: lpc32
author_rank: Frequent Contributor
timestamp: May 05, 2014, 03:48:01 pm
content: 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?

author: 8086
author_rank: Super Contributor
timestamp: May 05, 2014, 04:20:20 pm
content: Quote from: lpc32 on May 05, 2014, 03:48:01 pmProbably a diode. I can't see the protrusion you're talking about.QuoteDoesn't look reflowed to me. Probably drag soldered.QuoteYeah, 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...QuoteCurrent sense presumably.

author: lpc32
author_rank: Frequent Contributor
timestamp: May 05, 2014, 04:26:47 pm
content: Quote from: 8086 on May 05, 2014, 04:20:20 pmThe 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.QuoteIt's on the USB shield.

author: Balaur
author_rank: Unknown
timestamp: May 05, 2014, 04:36:19 pm
content: Quote from: lpc32 on May 05, 2014, 04:26:47 pmIt'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.

author: 8086
author_rank: Super Contributor
timestamp: May 05, 2014, 04:53:54 pm
content: Quote from: lpc32 on May 05, 2014, 04:26:47 pmProbably a stray bit of flux, or glue, or something. I don't think it's meant to be there.QuoteLow side current sensing, is easier to implement as Balaur said already.

author: lpc32
author_rank: Frequent Contributor
timestamp: May 05, 2014, 06:16:07 pm
content: 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.

author: SeanB
author_rank: Super Contributor
timestamp: May 05, 2014, 07:13:47 pm
content: 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.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: May 05, 2014, 09:52:21 pm
content: 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

author: zapta
author_rank: Super Contributor
timestamp: May 06, 2014, 04:40:17 am
content: 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

author: zapta
author_rank: Super Contributor
timestamp: May 06, 2014, 03:16:06 pm
content: Quote from: lpc32 on May 05, 2014, 03:48:01 pm0.5 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.

author: zapta
author_rank: Super Contributor
timestamp: May 06, 2014, 03:18:26 pm
content: Quote from: edavid on May 06, 2014, 03:05:56 pmGood idea. Here is a recent examplehttps://www.eevblog.com/forum/reviews/another-helping-hand/msg0/#new. I would add the Bakku pcb holderhttp://www.dx.com/p/baiku-bk-687-stainless-steel-repairing-pcb-holder-for-cellphone-silver-284069#.U2j9LK1dUog

author: Stonent
author_rank: Super Contributor
timestamp: May 07, 2014, 06:27:16 am
content: I think the person who did the soldering was having a fit of sneezing while doing it.

author: zapta
author_rank: Super Contributor
timestamp: May 07, 2014, 11:13:13 am
content: Quote from: Stonent on May 07, 2014, 06:27:16 amAnd I thought this was flux ,..

author: lpc32
author_rank: Frequent Contributor
timestamp: May 09, 2014, 10:03:02 pm
content: 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.

author: lu33390
author_rank: Newbie
timestamp: March 03, 2015, 03:41:11 pm
content: 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 .

author: Rick Law
author_rank: Super Contributor
timestamp: March 04, 2015, 02:40:57 am
content: Quote from: zapta on May 06, 2014, 03:16:06 pmThe photo shows R050 = 0.05 ohm.

author: aargee
author_rank: Frequent Contributor
timestamp: March 04, 2015, 06:48:12 am
content: What I find funny is that the silkscreen is all mirror imaged.