On 11-03-17 09:13 AM, jb-electronics wrote:
Gaston, thanks for your view as well, but I think I don't really get it. Even if the LED is not linear, so what? The current meter should still show the correct value, right?
I think the issue is that an LED - Like a neon Light will change the resistance it shows in a circuit as the current varies. if you are trying to set up a circuit to test an ammeter it is more straightforward to use anly resitive components.
The input impedance angle is based on teh fact that the A to D will itself act as a resistor in parallel with the resistor that you are using to create the voltage drop. Thus your resistor may look like a slightly smaller value to the rest of the circuit.
The Old VTVM meters got around this by using a grid which did not draw (very Much) current)
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