wrong adc for extruder at room temp

I've replaced the r2 main board with a ramps 1.4/2560 board set. I kept the original extruder with its thermistor. I kept the original thermistor table (table 1 for Epcos 100k 4.7k pullup). I turned on the SHOW_TEMP_ADC_VALUES to see the ADC values when setting the ext0 temp. At room temp, I get an ADC value of about 319 which gives a temperature of about . I think I should be seeing something like 977. The resistance of the thermistor at room temp is 100k ohms, so I think a table for 100k thermistor should work as a starting point. I'm assuming that the ramps board has the 4.7k ohm balancing resistor. I have not changed the downtown board yet, although I have the modified version from partsbuilt.If the thermistor ground is not good I'm assuming that there would be fluctuations around the set temperature not a whole sale offset. Any ideas about how to fix the ADC offset so that I can then create a valid thermistor table.

 

The Robo thermistor table is for a thermistor with a Beta of 4100 which is very close to the the 3950 thermistor. I suspect Robo is using a 3950 thermistor because I use a 3950 table with the Robo thermistor or the Chinese 3950 thermistors and get the same results.

I have been using the Ramps 1.4 board for awhile. It does require the downtown board change because the ramps grounding is entirely different and you want an isolated thermistor on the hotend. It requires a code change for the different I/O and I use separate 12v for the fans and 24v for the bed/hotend. This requires a simple mod to the Ramps. You do need separate 12v and 5v supplies. I have this completely documented with the code you can just load from the LCD. I have posted so many things that my google drive is filling up. If there is a way to pm me I will send you everything.

You might contact Jonah@Partsbuilts.com. I have used his first proto's of the board replacement which just mounts the Ramps and step down Power supplies on a PCB that is plug compatible with the original R2 board. I have all of the documentation for that as well. The final board is in China right now and you might want to wait for it's release....it has some neat new features.