low voltage for both data pins (1v)

by **andrew nordyke** » Mon Dec 03, 2012 3:54 pm

Hey, I'm getting a voltage read of 1w for both data pins. The reading between pins 1 and 4 is spot on at 5w. What could be causing this? I double checked that everything was in the right place with correct polarity and even went around touching the soldering iron to to all the joints, making sure it was a solid joint. They all look fine, there are no bridges between anything. I didn't clean up the flux residue. Any suggestions?

Thanks

by **adafruit_support_bill** » Mon Dec 03, 2012 4:01 pm

1W? I think you mean 1V.
Post photos of the front & back of the board and we'll take a look.

by **andrew nordyke** » Mon Dec 03, 2012 4:14 pm

Haha, yes of course, volts. Pictures of front and back attached.

by **adafruit_support_bill** » Mon Dec 03, 2012 4:19 pm

Assembly looks good.
What voltage do you get with one probe on each end of R3?
What voltage do you get with one probe on each end of R4?

by **andrew nordyke** » Mon Dec 03, 2012 4:29 pm

R4 reads approx 1.8v
R3 reads approx 1v

by **andrew nordyke** » Mon Dec 03, 2012 4:35 pm

the corresponding resistors measure the same voltage for R1 (1V) and R2 (1.8V)

by **adafruit_support_bill** » Mon Dec 03, 2012 4:42 pm

The ratio is about right, but the total of the two should be the same as what you measure across pins 1 & 4 of the USB connector.
Measure Pins 1 & 4 again. Make sure you have a fresh battery in your meter and check it against a known voltage.

by **andrew nordyke** » Mon Dec 03, 2012 4:48 pm

Brand new battery but in two days ago, today is the first day i've used it since putting it in. Reading a AA battery gives me 1.5V.
Is it possible that I damaged the pcb? Would that cause what I'm seeing? I was using an alligator clip while soldering to hold it in place, near where pins 2 and 3 are in the middle. I tried not to get too close, but i do see a little surface scuffing. Does that affect anything? You can see it in the attached photos from before

by **adafruit_support_bill** » Mon Dec 03, 2012 5:12 pm

The scratch does not appear to have damaged the copper traces.
Are you still getting 5v between pins 1 & 4?
As you can see from the schematic, the resistor pairs are connected between 5v and GND. The sum of the voltage across each resistor in the pair has to add up to the voltage across pins 1 and 4. It's the law! (Kirchhoff's, that is)

by **andrew nordyke** » Mon Dec 03, 2012 8:33 pm

Yeah, I'm still getting 5v between pins 1 & 4. Not sure what to say here, I'm a bit of a beginner with all this. Still getting 1v for both data pins.

by **adafruit_support_bill** » Mon Dec 03, 2012 8:49 pm

How are you measuring the data pins? Between GND (pin 4) and the data pin?

What do you get when you measure between the data pin and 5v (pin 1)?

by **andrew nordyke** » Mon Dec 03, 2012 9:02 pm

Yeah, everytime I've measured it,i've done it between GND (pin 4) and each data pin, to where pin 4 and pin 2 would give me 1v, and pin 4 and pin 3 would give me 1v.

I had never measured between the the data pins and 5v (pin 1) before... just tried it, gives me 1.8v between 1 & 2, and between 1 &3. Is that what i should have been looking for all along? I had been following the tutorial on your site (http://www.ladyada.net/make/mintyboost/solder.html), and there it says that when you measure between GND and the data pins you should get close to 2v. The photo on the page even shows a readout of 1.97v on their board btw those pins. It says nothing of the measurement btw 5v and data pins.

Have we figured something out... ?

by **adafruit_support_bill** » Mon Dec 03, 2012 9:27 pm

Have we figured something out... ?

If we believe the evidence, you are in clear violation of the laws of physics. :shock:

The voltage between pin 1 and pin 2 plus the voltage between pin 2 and pin 4 must add up to the voltage between pin 1 and pin 4.

The 1v/1.8v measurement is consistent with what you measured across the resistors. But it doesn't add up to the 5v you measure between 1 and 4. This is really a pretty fundamental law and a very simple circuit. I can only conclude that there is something wrong with the measurements.

Not sure what to suggest here. Maybe post photos of your meter settings and how you are taking the measurements?

by **andrew nordyke** » Mon Dec 03, 2012 10:02 pm

: IMG_1602 copy.jpg (402.44 KiB) Viewed 1025 times

Oh jeez.. well hopefully in the end we can blame my amateur multimeter skills. I've attached the three readings that I came up with. Btw 1 & 4 = 5v / 3 & 4 = 1v / 1 & 2 = 1.8ish volts

Please tell me I clearly have no idea what I'm doing, haha

by **andrew nordyke** » Mon Dec 03, 2012 10:05 pm

heres the other two photos

low voltage for both data pins (1v)

low voltage for both data pins (1v)

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