Ramps 1.4 giving improper temp readings

I am getting the following read out in pronterface:

ok T:135 B:357

The odd thing is that I get the same even if I unplug the thermisters. It is like it isn't even picking up a temp reading from them at all. I verified the pin layout from: [reprap.org] which is in sprinter. I am not sure how to proceed?

It is on a knock off Ardunio mega 1280 running sprinter firmware.

The board is driving the motors, but there are also issues with the endstops which do seem to be wired correctly.

I am thinking that one of the boards may be toasted? Thoughts? Suggestions?

... check for shorts and correct/meanuíngfull voltages at the pins in working condition (e.g. if the voltage changes with changing temps and/or activated endstops).

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Just a follow up ... I unplugged the ramps board and tried wiring a thermister to gnd and analog 8 10, 13, 14 on the arduino. I am pretty sure it is a dead board as the readings never changed.

Edited 1 time(s). Last edit at 01/19/2012 03:57AM by zomie.

... could it be an issue with the internal or external pullup-resistor?

If you haven't activated the internal pullup and wire a resistor from the pin to GND you'll only measure GND-level.

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Sounds like the motherboad setting in Configuration.h does not match your version of RAMPS. For v1.4 you need to set it to 33.

for the analog pin to read the thermistor it uses the charge time of a capacitor to calculate it.(it can't measure resistance directly) The ramps board has the resistor and capacitor hardwired into it. Look through the RAMPS 1.4 wiki page and make sure all the smt resistors and capacitors are present and wired properly.

The only other hint I can provide is that I would get similar readings from the thermistor when the RC circuit +5V was removed but it still had a ground.

Trace out the circuit and use a multimeter but be careful not to short anything out.

Well, I ordered another ramps board and arduino combo and am getting the same issue. It is very damn odd.

I even disconnected the ramps board and left the arduino bare and I get the same readings back on the new arduino.

It is defined as board 33 too ...

Any other ideas?

Try swapping the thermistors of the bed and the hotend and see is the readings switch also. Maybe your thermistor leads are shorting out somewhere.

I've only had this problem once, I was using a breadboarded version of ramps. When the board was not getting 5V from the arduino, it would give me readings like this no matter what the temp was.

Yeah they don't switch out.

Zomie, Interested to hear if you have solved this issue? I am now having a similar issue. After a few weeks of running fine, I now get a temperature reading of T:252 from the RAMPS/ARDUINO, this is regardless of thermisters being plugged in or not. I was about to order a new set of boards but I read here that it made no difference for you, is it a firmware issue? Did you manage to solve this issue?