Wrong temp reading on RAMPS 1.4

Hi all!

I have just finished my RepRap build. I bought a full kit, including soldering from MakerGear.com

When i started to power up, I started to talk with the people in the norwegian reprap forum, reprap.no

I started with after advice from the people there to use Sprinter firmware, so I uploaded that after I changed the firmware from 1.3 to 1.4...
I downloaded pronterface for the communication with the printer.

I have not connected the atx powesource yet, only usb, i have not connectet the heatbed to the RAMP pcb, and i have only one thermistor, that is to the hot end, the kit did not include a thermistor to the heat bed, and after some reading i couldn't find any concrete demands on that the heatbed needed one..

I connected the printer with com4 and the right speed, i pressed the "Get temp" and it gave me a reading of 45 degrees and the heatbed on abot 70 degrees.. (don't remember the exact numbers) keep in mind i have not connected any power to the printer, and the heatbed is not connected, and neighter is the thermistor for the heat bed..


Is there somting I am doint wrong, or is the card busted?


Thank you all


-Kjetil Hansen

The Arduino microcontroller gets power (5V) from the USB cable and the thermistor circuit doesn't need the 12V power from the the ATX power supply to work. So, with RAMPS plugged in to the Arduino, you will get temperature readings. But, unless you have the correct thermistor tables in the firmware, the temperature readings will be wrong.

You do need a thermistor on the bed if you want to use RAMPS to control your bed temperature.

brnrd Wrote:
-------------------------------------------------------
> The Arduino microcontroller gets power (5V) from
> the USB cable and the thermistor circuit doesn't
> need the 12V power from the the ATX power supply
> to work. So, with RAMPS plugged in to the Arduino,
> you will get temperature readings. But, unless you
> have the correct thermistor tables in the
> firmware, the temperature readings will be wrong.
>
> You do need a thermistor on the bed if you want to
> use RAMPS to control your bed temperature.


The funny thing about that is that the table does not have a thermistor connected, but still gives me a reading... And somone told me that the 100k thermistor i have is defult in the sprinter fw...

what can it be??