ok I dont get this...
i was trying to lower the 5v pin voltage of arduino mega to something lower so i connect a diode (1n4007) to the 5v pin of mega, and measured with a voltmeter with respect to ground. i was expecting something between 4 and 5v, but i am getting 6V! :o
why is this?
Put a new battery in your DVM.
.
I dont have a new 9v battery right now, but i have measured the battery with another DVM (same cheap model) and it shows 8.5v or something like that... but, I dont know about the battery on that other DVM... (and if i measure the diode output with that other DVM, it gives different voltage but still ABOVE the 5v input...)
anyway I have just tried adding a load (led + 220 ohms resistor) to the output of the diode and now it seems to work ok... it reads 4.98v before the diode, and around 4.2v after, wich seems more logical to me...
but still i dont get why...
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ok thanks. will try to get a better one...
just trying to understand why it seems to work sometimes... i have now tried powering the arduino via usb and it works, but not if arduino is powered from a wallwart at around 9v...
thanks again
I'm actually also measuring slightly higher voltage that the input voltage on the end of the diode, with a 1N4001 powered off 5v bench supply.
I don't see as large a difference as you do, but I measure 5.04 before the diode and 5.21 after it.
Without any load on the diode, there's no way for it to be less than 5v, and I think it must be picking up noise or something, analogous to a floating pin? That's the only thing I can come up with.
Notice how when you put even the slightest load on it, you get something like 4.3 - it's just when there's nothign connected to the end that you get odd results.
If the output of the diode has a higher voltage, it implies that the input contains a substantial AC component.