Just wanted to say a big thanks to all of the people working on this. I’m not sure if someone already has mentioned this, but I was thinking it’d be good to be able to calibrate your probe without the need to change the code. I found the equations to solve for A, B, and C via this site (it’s in the javascript alex_cal_draw.js) and came up with the following:
double A, B, C;
void setup()
{
Serial.begin(115200);
double R1, R2, R3, T1, T2, T3;
R1 = 51000; // resistance in ohms
T1 = 22.45; // temp in celcius
// Boiling water at 700ft altitude
R2 = 3297;
T2 = 99.3;
// ice water
R3 = 155500;
T3 = 0;
T1 = T1 + 273.15; //convert all temps to kelvin
T2 = T2 + 273.15;
T3 = T3 + 273.15;
C =((1/T1-1/T2)-(log(R1)- log(R2))*(1/T1-1/T3)/(log(R1)-log(R3)))/((pow(log(R1),3)-pow(log(R2),3)) - (log(R1)-log(R2))*(pow(log(R1),3)-pow(log(R3),3))/(log(R1)-log(R3)));
B =((1/T1-1/T2)-C*(pow(log(R1),3)-pow(log(R2),3)))/(log(R1)-log(R2));
A = 1/T1-C*(log(R1))*(log(R1))*(log(R1))-B*log(R1);
}
Those were my values for the IKEA Fantast thermometer. Right now it’s all being calculated in the setup and values are hard coded. But there’s no reason we couldn’t make a few buttons where you put your probe in boiling water, then hold a button for 5 seconds, ice water, etc. It could all be done via a smart phone or web interface and then just store the values in non-volatile memory. This would allow people to calibrate if they swap out probes, or if it seems to be less accurate over time (not sure if thermistors loose accuracy over time).
Also we could make it really smart, and detect the altitude of the core based on IP, then use that to calculate the actual temp of boiling water.
I connected the tip and NC switch to analog in and the sleeve to gnd.
I believe I've set this up how you suggested. Assuming I did, this will affect my R when calcuting temp. Should I use low tolerance(1-2%) resistors for the 1Ks?
Makes sense and sounds like a good best practice. I have updated.
I'm thinking you mean right after J5 input, in which case I have added them and that totally makes sense. Hopefully I'm not misunderstanding.
Bah, right you are. Fixed
I picked a connector here that seemed to be the most common among commercially available "smoker" fans/blowers and also added standard header pins in to more easily allow connecting anything else. Ideally the fan would use the barrel connector.
Also now that I'm using 1K resistors I changed the 2 330 blower output pull downs to 1K's for less parts.
Thanks for all the feedback! Would you mind giving it a once over before I start putting together the pcb?
You can leave it floating… it’s perfectly ok… unless you put a big long wire on it out to an external switch, then you are probably going to want to mimic the other switch connections with a series 1k resistor for ESD, but no extra 10k pull up.
EDIT: This is a good point, all products that get enclosed like this one should… will need some way to access the MODE and RESET buttons. RESET is easy enough… MODE is a little trickier. I guess start thinking about it now There is a plan to get the function of the MODE user definable to one of the digital inputs if I remember correctly.
Ok, I don’t plan on attaching an antenna to it, so I’ll leave it floating Ya, I figured I’d leave paper clip size holes above mode and reset on the enclosure for now.
That's how a lot of the router manufacturers (and tons of other projects) do it! It doesn't seem to bother the hundreds of thousands (if not millions) of customers who have devices like that in their home already!
It is portred to the Spark, and it compiles correctly.
You can uses NUM_THERMOMETERS to determine how many NTC’s you want to measure.
I use the code in a project where I control a woodburner that heats my house.
Enjoy!
Marcus
It proves it works with peltier elements. BTW you can find peltier elements on DX.com for $6,-!
The principle is simple, a peltier element generates a voltage difference when the temp on 1 side is a lot higher / lower than on the other side. So you need a cooling ‘element’ (Sorry I don’t know the correct English term).
The energy generated is more than sufficient to drive your ventilators and a Spark.
About the connectors, in a greasy environment I would opt for a fixed connection, or if you really want a connector, use an RCA audio connector.
These connectors have a bigger contact surface.
Succes!
Marcus
@Hypnopompia and I visited their booth at Maker Faire. We considered plugging a Spark into the USB on the stove, but they had just emptied it and were going to have to refill it and reignite it. Then, of course, there was no reliable wifi at the Faire for the Core to connect to…
The BioLite stuff is very interesting–their smaller product has been in stores for some time but I have never seen one in the “wild” and I camp every month. It’s a great concept, but a little big and bulky and heavy for outdoor gear. It is interesting that they are running a kickstarter for a “base-camp” larger version when they already have a product out and in lots of retail stores. That might tell us something about their revenue stream. The new product might shift their target audience to hunters and preppers who don’t care about weight and bulk, which could be a smart move.
I live in Sweden, so I have no change to see the product in real life. My impression is that the product is basically designed for 3rd world countries. You might know that every year 2 million people die due too cole mono oxide poisoning. The stoves they make are high efficiency burners that don’t produce any emissions, that save lives. The burning principle is based on the http://en.wikipedia.org/wiki/Rocket_stove principle. A very interesting technique!
Having a Peltier element to power the ventilator and your phone is a nice extra!
I have built a “rocket-style stove” out of a used mini-beer keg. These stoves are well insulated, burn for a long time and pump out heat, but carbon-monoxide still comes out, like any burning process. I have always thought of these stoves as more efficient primarily due the the insulated fire box. All the heat goes up the flue, which is an advantage.
I don’t see the stoves as being particularly safe from a CO poisoning perspective. They burn hot and tend to have very little smoke due to secondary combustion of gasses, but they are not magic. I see the BioLite in particular as being aimed squarely at the First World problem of charging your smartphone while camping.
Hi,
We’re not in a debating club but here are some links. This where I got my info from:
And much more documents like those.
Off course there will be carbon-monoxide produced by the stove, only far less then from a bad burning open smoldering fire in a badly ventilated hut, or tent. That’s what I meant, bad badly communicated
@marcus the peltier devices are cool. I may come back and visit them later as an optional way to power this device. If you want to try to put something together that would be cool.
I finally got the PCB put together for this project and there were a few minor schematic tweaks since I last posted. I still have a few tweaks to make to the PCB layout(trace widths and silkscreen) before sending to a fab house by Monday.
There is a plan to get the function of the MODE user definable to one of the digital inputs if I remember correctly.
Ya, I figured I’d leave paper clip size holes above mode and reset on the enclosure for now.
but here are some links. This where I got my info from:
