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Can UNO32 read negative voltage?
12-06-2012, 05:59 PM,
#1
Can UNO32 read negative voltage?
Can UNO32 read negative voltage?
If not would it be a problem if there are negative voltage spike on the line I am monitoring with one of the analog input?

I am monitoring a line with 3v spike (spike is around 5 us) and I have seen using a scope that there are also negative spikes (-3v 5 us). I tried using a diode to block the negative spike but I think the spike is too weak or the diode is not fast enough because even the positive spike was not able to pass the diode. I plan to just connect it to one of the analog in, I'm just worried that it might damage the A/D the Pinguino.
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12-06-2012, 06:39 PM, (This post was last modified: 12-06-2012, 06:40 PM by pingotg.)
#2
RE: Can UNO32 read negative voltage?
I don't think it can but look at the Microchip device data sheets (*). I would not be surprised to find such a spike could damage the chip!

(*) that's the ones from Microchip - for some reason people seem to ignore these vital data sheets!!!

John
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12-06-2012, 10:26 PM,
#3
RE: Can UNO32 read negative voltage?
Really... No...


But you can always use an operational amplifier as the lm324 and adding a dc signal, which allows to see when the signal is in-3v 0v view, this would be increased by a 3V dc signal, however this would generate a problem you when you're in 5v 8v and you could see this would damage the microcontroller, then you must make a minimum of one voltage divider leading 8v to 5v, or use the same package that has 4 operational, and give a negative gain for attenuating the signal, either of 2 things is valid ... This process is called signal conditioning, we can not always connect your sensor directly to microncontrolador, we usually prepare it ...
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13-06-2012, 01:42 PM,
#4
RE: Can UNO32 read negative voltage?
Most micro-controllers have diodes to supply and ground to protect the inputs. If you have a series resistance to reduce the maximum spike current, the inputs are probably safe - e.g. 10mA shouldn't break anything. If you want to measure a negative voltage, you should invert it. If the voltage that you are measuring has a negative offset, you may be able to shift it positive using an opamp buffer.
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14-06-2012, 05:31 AM,
#5
RE: Can UNO32 read negative voltage?
Thanks everyone for replying! I'm glad to know that there is a protection diode. I did proceed with my project measuring the signal directly without an OP amp, I just used a voltage divider (9k/11k ratio) and it worked.
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11-12-2012, 07:42 PM,
#6
RE: Can UNO32 read negative voltage?
Ok, first of all the spike is never too weak. The diode that you are using probably doesn’t support switching at that high frequency. Secondly most of the microcontrollers have protection mechanisms but not all so please do check your data sheet to see what limits they have provided to be measured with the ADC.
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