23 replies to this topic

[Chris Walker]

Have you tried using a pull down resistor? Quickly looking at all the example circuits on the datasheet for the LM35, it looks to me like they have some kind of path to ground.

Also, according to the neduino processor datasheet, only AD0-3 have pull up resistors, A4-7 do not?

A4 and A5 are not GPIOs. They are dedicated analog inputs. So no pull-up resistors.

Chris

[Marius]

I have a 100k pull-down on the pin. Maybe I should go a bit lower?

[sterned]

I am able to reproduce a similar situation to what Marius has encountered, the LM35 reading jumps around inconsistently for me from the analog input pin. When I put a voltmeter on the wire (while everything is still connected as is on the board, bridging voltmeter terminals from A5 to netduino ground - same as sensor ground) it is a very steady 196 mV, which is exactly as expected. During the constant 19.6 mV from the voltmeter, the netduino is jumping significantly, +/- 150% of the 196 mV reading. Here's the crazy part, when I disconnect my laptop from wall power, and run off batteries, the analog input pin falls exactly in line with the reading I get directly off the sensor. Plug the laptop back in and the analog input goes haywire again. I can reproduce at will by cycling the switch on my surge protector. Any ideas what would cause this or how to remedy it?

[sterned]

I should add that at the moment, I've only gotten so far as to be able to spit my "temperature" out to the immediate window via a debug.print statement. I'm running off of two different Toshiba Sattelite laptops, which both produce exactly the same results.