Analog inputs issue on standalone ATMEGA2560

[darcy_d]

Hi all, I have recently built my own board for a project which uses a atmega 2560. Have had the pcb's made and have uploaded my code and got it all working but have noticed a few issues with the analog readings.

I have 10k pulldown resistors on some sensors to be able to show when the sensor wire is broken or been disconnected. They are pressure sensors and hall effect sensors so read 0.5v - 4.5v in normal operation so when disconnected i'd expect to see 0v.

Some of the sensors do indeed read 0v when disconnected but some read 1.1v and this has been confirmed with my multimeter the pin does indeed read 1.1v or thereabouts ( 1.05-1.09) on the multimeter).

Given this, I am assuming it has to be pcb related but nothing stands out to me. I have read a bit on the Aref having a possible 1.1v reference internally if booted that way or along those lines so am wondering if its something to do with this ( only reason i can see 1.1v being shown) as i don't have Aref connected to anything on the MCU.

Is there a logical explanation to this or something wrong with my pcb design?

Thanks,
Darcy

[camsysca]

Problem likely is evident in the schematic you didn't post. I don't draw schematics in my head from paragraphs of text, so I'm sorry, I can't help you more.

[darcy_d]

Sorry couldnt see where to upload pictures,

[darcy_d]

[camsysca]

Well, I asked for that. It's not a schematic in my books, but I'm old school. I would call that a point-to-point wiring diagram.
Hopefully someone will come along to help you. I'm out.

[darcy_d]

Its to make reading them a lot easier using named nets rather than showing each individual wire which would get overly complicated to read.

A single net goes Analog input - Sensor wire which is linked to resistor to ground thats all for each one. If you want ill draw it seperate but this is the schematic straight from my pcb software that i designed so thats all i have but ill redraw a portion of it from scratch to help people that dont understand this.

[darcy_d]

This is a basic version of how each analog input is connected and how the pulldown resistor is wired.