Hi, I have a u12 providing power to an EI1040, and the 5v from the u12 is pulsing. I have uploaded a picture of the connections between the u12 and ei1040. A dc meter shows 4.99 vdc going to the 5v input, but a scope signal shows a pulse train of ~30Hz pulses.... which have a dc value of ~5v, but pulse on and off. This (pulsed) 5v is also setting the gain of the EI1040 to 10.
I'm thinking that the 5v in should be a dc value, and that maybe something is not right with the e12? (maybe a smoothing capacitor is open?).
Can you confirm that this pulsed 5v is correct or incorrect?
My end problem is that the output of the amplifer (which is connected to a strain guage) is jumping around, but should be steady. The strain guage seems to be reading correctly... (using an external power supply.)
If the 5v power in should be a dc value of 5 v, can you please confirm what I might need to repair this? The EI1040 is new (bought it about 2 weeks ago).
Thanks! Dan
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+5V on a U12 is the the USB supply voltage. Same as VS on all our newer devices. See item 1 in post #13 of old forum topic #4376 about bridge excitation options:
https://forums.labjack.com/index.php?showtopic=4376
It looks in your scope picture like voltage is pulsing by 500 mV. Is that right? I would say 50 mV is very normal, but 500 mV seems like a lot. If you disconnect everything from the U12 and just look at +5V on the U12 do you see the same thing?
Do you have software running that is making the U12 LED blink? I just measured the effect of the LED on my USB hub, using LJlogger.exe to turn the LED on and off, and the extra current of the LED causes a voltage drop of about 11 mV for me.
I just tried a couple of new tests.
1. After being unplugged for a while (several days), I plugged the interface box into the computer's usb port. The GND to 5V voltage on the amplifier module showed a ~200mV pulse... I'm expecting to see ~+5v.
2. I then unplugged the interface box from the computer usb port, and plugged it into one of my iphone charger modules. The GND to 5V voltage on the amplifier module immediately jumped to ~+5V, with little or no noise (no pulse waveform, etc)
3. I then unplugged the interface box from the iphone charger, and back into the computer usb port. Now the GND to 5V voltage was at ~+5V, with no noise (same waveform as when plugged into the iphone usb charger (#2).
Lastly, I unplugged everything overnight, and when I tried the 3 steps again, I got the same results (#1: 200mV, #2: 5V, #3: 5V).
I have attached files to show the oscope waveforms...
It seems that the usb port on the computer doesn't provide enough current to charge up some capacitors somewhere on the labjack board, but it can provide enough current to maintain a charge in the capacitors?
Any suggestions, hints, or recommendations?
I might have uploaded the wrong pics...
These are labeled.
There are a couple things we can try:
1) Use a powered USB hub. A USB hub with a separate power supply may be strong enough to power up your setup.
2) There may be a shorted / damaged component. Try removing the amplifier. Does that allow the USB port to power up the U12? If not, disconnect any other items from the U12. If removing the amplifier helped that we need to troubleshoot the amplifier.
USB ports can normally supply 500 mA, but not all ports are equal. Ports on laptops are particularly stingy.
Thanks for the suggestions.
The amplifier is new, I purchased a replacement before I posted the first comment. I'm thinking that's still good.
Let me try the powered USB hub... the portable is an old Compaq Presario running windows XP, and the application software. The easiest solution would be to use the computer-s/w setup as is, with a powered USB, if that indeed works as we hope. My thinking is that the USB port doesn't have the muscle to power up the interface box.
I'll let you know what happens.
Thanks again for your help. Dan