Timeline for Analog thermistor readings are wrong
Current License: CC BY-SA 4.0
30 events
| when toggle format | what | by | license | comment | |
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| Jun 13, 2019 at 11:48 | vote | accept | marsisalie | ||
| Jun 12, 2019 at 13:49 | comment | added | Dave X |
Looking at your referenced diagram, you are connecting AREF to 3.3V, but don't have an analogReference(EXTERNAL) in your code. arduino.cc/reference/en/language/functions/analog-io/… says not to do that since it shorts the external and internal references together during the analogueRead(). Maybe that could be causing some odd transients during the ADC switching?
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| S Jun 12, 2019 at 9:28 | history | suggested | brasofilo | CC BY-SA 4.0 |
Grammar. Highlighted text instead of redundant "question". Removed "edit". Added tag to enable syntax highlighting
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| Jun 12, 2019 at 5:09 | review | Suggested edits | |||
| S Jun 12, 2019 at 9:28 | |||||
| Jul 29, 2017 at 9:59 | comment | added | Majenko | @NickGammon Looking at the edited question with the code included it is plain that the resistor is not the problem either - so there is nothing about my comments that can be converted into a correct answer, and I won't post an answer I know to be blatantly incorrect. | |
| Jul 29, 2017 at 7:53 | comment | added | Majenko | @NickGammon even after he negated (correctly) my supposition. The thing about VCC is wrong and cannot be the answer. The mentioning of the wrong resistor value in a calculation I take as a copy and paste from original source not his modified source. With no clarification on if that actually is incorrect in his code I have no valid answer to post. | |
| Jul 29, 2017 at 7:48 | comment | added | Nick Gammon♦ | @Majenko - the OP has asked you to post your supposition as an answer. It can't get much clearer than that. :) | |
| Jul 29, 2017 at 7:44 | comment | added | Majenko | @NickGammon it is pure supposition at the moment. It looks to not be the correct answer so far, so doesn't deserve to be an answer. | |
| Jul 29, 2017 at 6:32 | comment | added | Nick Gammon♦ | @Majenko - comments under questions are for clarifying the question. If you think you have an answer it is preferable to post it, so it can be accepted and/or commented on. | |
| S Jul 28, 2017 at 11:12 | history | suggested | Sonali_B | CC BY-SA 3.0 |
coreected spelling ,fixed grammer,improved formating
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| Jul 28, 2017 at 9:21 | review | Suggested edits | |||
| S Jul 28, 2017 at 11:12 | |||||
| Jul 15, 2017 at 13:37 | answer | added | Edgar Bonet | timeline score: 4 | |
| Jul 14, 2017 at 13:07 | answer | added | dannyf | timeline score: 0 | |
| Jul 14, 2017 at 6:08 | answer | added | Jot | timeline score: 3 | |
| Jul 14, 2017 at 2:53 | comment | added | marsisalie | @Jot Sketch was added | |
| Jul 14, 2017 at 2:52 | history | edited | marsisalie | CC BY-SA 3.0 |
added sketch
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| Jul 14, 2017 at 1:28 | comment | added | Jot | @Majenko, for a thermister plus resistor the VCC drops out the calculation. It is relative to VCC. In the calculation the 5.0 could be used, and the actual voltage may vary, it may be 4.0 or 5.5V, it does not matter. That's the beauty of a thermistor. However, the slightest deviation in the calculation and the curve will change. EtienneGodin, where is the sketch ? (it is 1024 ADC steps, not 1023). | |
| Jul 13, 2017 at 23:34 | comment | added | marsisalie | @Majenko if you wish to summarize your intervention as an answer, I would choose your answer to close the question | |
| Jul 13, 2017 at 22:16 | comment | added | Majenko | True, that is... Don't forget 10K should be 6690, of course... | |
| Jul 13, 2017 at 22:15 | comment | added | marsisalie | @Majenko thank you for confirming this possible path for resolution; I suspected this for a while but since it was not really defined in examples, I tried to look for other issues I guess. It was overviewed in examples because the calculation cancels out; for example ADC value = R / (R + 10K) * Vcc * 1023 / Vcc become ADC value = R / (R + 10K) * 1023 | |
| Jul 13, 2017 at 21:57 | comment | added | Majenko | You must be referencing VREF somewhere in order to calculate the resistance. After all, the resistance is measured by the voltage drop across it, and to convert the raw 0-1023 value of the ADC to a voltage you need to calculate it with respect to VREF. If you use the wrong value you will get the wrong result. 5V is not 4.91V. | |
| Jul 13, 2017 at 21:50 | comment | added | marsisalie | @Majenko (1) Assuming 5V, measured 4.91ish; but in my sketch (working on it) I don't seem to reference the VREF at all, like example sketches - maybe I should check it out in greater depth; (2) Good point, yes the thermistor is at the end of a long wire. But yet, if I measure using the ohmmeter directly on the cable, (fig 1, result in green) the thermistor is still at the end of the same long wire, like when the arduino read (fig 1 in orange) | |
| Jul 13, 2017 at 21:24 | comment | added | Majenko | 1. Are your calculations assuming a VREF of 5V, or do you know the real reference (VCC by default) voltage? 2. Is your thermistor at the end of a long wire? | |
| Jul 13, 2017 at 21:09 | history | edited | marsisalie | CC BY-SA 3.0 |
added COEFFICIENT values, thermistor and resistor specifications
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| Jul 13, 2017 at 20:59 | comment | added | marsisalie | @Jot yes I have the exact values for this, I will update my post with the relevant info. This site is awesome isn't it (thinksrs). Will check for the sketch too | |
| Jul 13, 2017 at 20:53 | comment | added | Jot | What is the exact value of the 7k resistor ? Do you know the type of the resistor, to be able to find the A, B, C and β values in the datasheet. This online calculation might be useful: thinksrs.com/downloads/programs/Therm%20Calc/NTCCalibrator/… Please show your sketch. | |
| Jul 13, 2017 at 17:52 | comment | added | marsisalie | @dandavis OK I will try this thank you for suggestion, will post an update when done | |
| Jul 13, 2017 at 17:41 | comment | added | dandavis | try plotting VREF over same timeframe as read with a dmm, do you see distortion? | |
| Jul 13, 2017 at 17:28 | review | First posts | |||
| Jul 13, 2017 at 18:44 | |||||
| Jul 13, 2017 at 17:24 | history | asked | marsisalie | CC BY-SA 3.0 |