Thermistors and the Spark Core

Hardware
61

Ok, I threw up a project on hackster. Let's start the conversation over there!

http://www.hackster.io/natewyatt/smartbbq

62

we arent going to get much community traction on hackster. why not a spark forum thread??

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63

This was a question I asked before.. what's the attraction of Hackster.io? Why not something larger like Instructables or learn.spark.io :smile:

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64

ha. i meant it a little differently.
i understand the attraction of hackster. once a project is nice polished and complete, we can drive people to that site. its better than instructables because we can eventually make a 1-click interface to allow people download the firmware to their spark core.

what i meant was that hackster isnt great for discussion. i think there are a few things that we can discuss about the hardware and software side of this projectā€¦

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65

Sorry, not sure why I didn't see this post until now. I've removed from hackster and reposted here: SmartBBQ: WiFi controlled 4 probe BBQ controller with blower output - Project Share - Particle

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66

I know this is an old thread, but I'm running into basically the same thing you got here Avidan. I've calculated and recalculated my constants. They work w/ a 5v reference but not 3.3v. I don't see how this has any effect on the constants. Anyone have any ideas?

67

i could have sworn we got it working after @BDub did some magic. but now im not remembering the results of the process.

i think it was a 0.1uF ceramic capacitor. do you still have it working @BDub?

68

Ok, I finally figured out the issue. It has to do with the reference voltage. @Avidan in your Arduino example when you wired 3.3v to your fixed resistor you also need to wire 3.3v to REF pin and add the following to you setup() block.

analogReference(EXTERNAL);

From my understanding the reference voltage for the uC on the Spark Core is fixed at 3.3v. When I measure it I was actually getting a slightly higher voltage. I scaled up the analog value based on my readings by adding this before proceeding w/ the calculations.

aval = (double) aval * 1.027;

So now my question is if this is the best way to compensate for the fixed reference voltage? @BDub, it sounds like you have some experience w/ this, do you have any insight?

Thanks!

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69

I donā€™t know if itā€™s relevant in this situation, but moving my supply voltage to a wall wart (instead of powering the Spark via USB) made a huge difference. Where my temps used to swing several degrees, now Iā€™m only seeing 1-5 bit changes for the thermistor (and single bit changes for the TMP36).

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70

Hi, my readings are all over the place despite harvesting a range of coefficients (heatermeter, forums etc).

Iā€™d like to revive this to ask if my breadboard is on target.

71

What is the external power supply for? Doesnt seem to be hooked up correctly

72

its not an external power supply, its the thermistor plug in. in this case, they look very similar.
http://ecx.images-amazon.com/images/I/21iJhsOiboL.jpg

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73

yep, as Avidan said, its the thermistor probe (ET73)

74

iā€™m intending tonight to take measurements of the various points (10k resistor, 3.3v* to GND, actual voltage across resistor, resistance of the probe from A0 to GND) per a post I found in the analog readings thread.
it just seems Iā€™ve done the generally right things. tonight iā€™ll run the sensor to A7, use the ground from that side for the cap and shorten the 0.01cap.

iā€™ll also introduce some delay between the measurement calculations of R and T etc.

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75

im looking forward to hearing your resultsā€¦its almost bbq season.

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