Hi,
I am using Mega2560 , trying to read Analogue value from an active device.
When I connect the load I am getting a drop in voltage from 4.2 to 5 V, It stays at 4.2 V. I have also noticed that the analog input is drawing more current than it is supped to.
I solved the issue using an non inverting op-amp.
is there any way I can do with out an-amp?
DO any one has any suggestions ?
Yes.
Post the wiring, the code & the datasheet for the 'active device'.
analog input is drawing more current than it is supped to
Analog input on a Mega is specified at 100 megOhm so it will draw virtually zero current (certainly not enough to measure without lab equipment). If there is a voltage drop it has nothing to do with the analog input. It must be external circuitry (the "active device" has very high output impedance).
I second simplesolutions. We need to see the details of the project.
Thank you for your reply.
I had a Zener 5.2V diode to protect from overvoltage. But this starts conducting at 4.2V but low current.
The device I used was the current limiter to 1 mA.
I took it off and all worked well.
This was the issue:) cheers thanks.
To protect the input from overvoltage or negative voltage, you can put a 10K resistor between the source and the analog input.
That will limit the current through the input protection diodes to a reasonably safe value, up to source voltages of about +/- 10 V.