Incorrect Thermistor Temperature Readings/Settings

Hello,

I recently bought this j-head hotend from amazon, and connected the thermistor to my Arduino Uno just to test it out because I thought that I may have to play around with some of the settings. I guess I was right, because when I connect to the printer in pronterface or repetier host, they both give me a value of 618 degrees.

The thermistor should be a 100k NTC 3950 Thermistor.

I checked the resistance with my multimeter, and it registered 100k Ohms like it should. If I disconnect one of the wires, the temperature reading in pronterface drops significantly (58 degrees), but then jumps around which is expected because nothing's conncected.

I have attached a picture of the settings in teacup configtool, and the reading in pronterface. I would appreciate any advice, thanks.

How do yo connect your sensor? Directly to your UNO?
You need a voltage divider with 4k7 ohms to measure it correctly.
When there is no divider the input gets full 5V which could be the 600°.

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Ah, I see. I had it connected directly to my UNO, I didn't know about the voltage divider.

Ok, two follow up questions:

1) What is a voltage divider? Is it just a simple 4k7 ohm resistor, or another circuit that I would have to build?

2) Could I change my R2 value to 0 in Teacup and not use a resistor (if that's what the voltage divider is)?

A note about the second question- I did try changing R2 from 4700 to 1000, but the temperature on pronterface said 636 degrees.

Of course your temperature stay at 636. The ADC measures the voltage and not the current. While your voltage is constant, 5V, the ADC is constant.

[en.wikipedia.org]

Z1 is 4k7
Z2 is your thermistor
VIN is 5V
VOUT is the ADC-input
GND is GND.

---

Triffid Hunter's Calibration Guide

--> X <-- Drill for new Monitor

Most important Gcode.