how far from the elements is the temp sensor?
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Sounds pretty good, if you're using arduino environment for programming you can easily add PID control which should stabilize the temp around the set point pretty well.
If you temp sensor is above your petri dish, I would worry the petri is blocking heat, and that the underside of the petri is actually warmer than you want. If you have a second temp sensor, it'd be worth it to put that below the petril, and see if the two sensors report different results.
I have code for a water bath that uses an arduino and an LM35; you might
be able to re-use some of that code if you like?
In particular, there's an LM35 reading function and some basic
temperature controls, and some failsafe code built in.
It's on github here: https://github.com/cathalgarvey/KettleKontroller
And it's attached. Currently set to 55C for the G.stearothermophilus I'm
trying to culture, you'll have to change that if you want to use it as-is.
Also if you're using it as-is, you'll need to play with "HeatPulseDur"
and "RestPulseDur": they cover how long to turn the heater coil on and
off during heating. Kind of like coarse pulse-width-modulation; you can
use different settings to get different rates of heating out of any
given setup.
Right now, it's pin A0 for LM35 input (with the LM35 on +5V), and heater
control is on pin 13 (In my case, controlling a relay which turns a
kettle on and off)
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Great call! :)
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...It's made of a very big christmas coffe cup ...
...The circuit is designed to be as secure as possible. And it is getting tested. ...
The lack of a durable surround for the heater is going to cut sales
down to a very few.
On 04/22/2012 03:07 AM, Mega wrote:
> Maybe, some shop sells cheap cooling boxes?
There are no retailers for partial products, just warehouse companies.
This kind of thing needs some design time and testing and thought.
You're not done yet.
On 04/21/2012 Mega wrote:
> 20€. Say 25. (I keep looking for cheaper parts, although here they
>> are already quite as cheap as possible)
Oh, you can do much better. A 1 Watt heater system can be run by a $0.5 microcontroller
and a $1 DC power supply, and $0.30 worth of passive parts, $0.75 for PCB,
and case parts of decent non-flammable materials for $1 and kit purchasing
time of $0.25 per each ==> $2.80 USD per kit. You could profit at a selling price of
$5 if industrious, profit less at a selling price of $10 if lazy. 20 eur is a
very low volume selling price for what you offer.
I'm not as pessimistic about diybio equipment evolution as byowired, but
to sum it up, you haven't mentioned anything novel or high value that
I'd design into a product yet. And your price ... ehh?
John
I dont think that styrofoam is a bad idea. Plenty of bird-egg incubators use it, and those are considered safe. If you really wanted to go safer you could use a thermal shutoff switch like those used in mcus to prevent damage.
I think that as in any situation you have a responsibility you not harm others and do your due dilligence, but out seems that you have taken that into consideration.
That said, I do not know what the market for incubators is, but dont be afraid to be entrepreneurial.
--A
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US http://search.digikey.com/us/en/products/PIC10F204T-I%2FOT/PIC10F204T-I%2FOTCT-ND/718268
> A relaise, that can stand 1A is not as cheap as you said, at least in my country. I looked for the cheapest components.
Use FETs. They handle that level of power if switched quickly by the 50 cent micro and cost $0.25.
Yes, and they switch very quickly, but may need some careful selection to shut off
completely when using a single DC supply voltage for everything...
Will you show us a sketch or schematic of your circuit? What temperature sensor
do you use? Are you using nichrome wire to heat? How many A2D or comparator inputs
are you using on your microcontroller?
Well commented code examples at http://wiki.sgmk-ssam.ch/index.php/Hands_On_AVR#SGMK_tiny
that have the main code chunks of a heater control done already.
John
John
That is $1 each in ones qty, so maybe you could use the inherent
temperature dependent volts in circuitry you already have. Often microcontrollers
take a known steady small current diode junction in the chip and arrange to
switch its voltage to the input of
the measuring ADC, with which you can use
a look up table of temperatures. A little more work in code and testing and
a whole dollar off! No big loss in accuracy for the range you care about.
Degrees C +/- 0.5 degree is easy. If there's not an internal convenient diode volts
to measure, you can add a diode and resistor to +DC power supply as your temp sensor
attached to a comparator/ADC input.
John
For reproducible results, it's nice to offload variables and pay the
extra 50c for a decent IC package.
Here's a good write up of using a diode for temp sensor.
It needs a volt reference, so pick a micro that has one of those.
Most MSP430 have one. (See below)
http://www.rst-engr.com/rst/articles/KP90APR.pdf
Here is some thermostat write up, and code for MSP430:
He uses a micro with a $2.50/ qty one price though...so some reading of the
datasheets of the minimal MSP430G2230IDR in 8 pin SOIC pkg for 0.76 USD qty ten, $46/qty 100
That one has internal temp sensor and 4 channel ADC 10 bits.
I need to start something with that one!
John
It's the physics behind all the temp sensors, the differences are in the implementation details.
Why would you pay more for a method or mechanism if you can't get any better results
than with the low cost method? You don't just always pay more, you shop for a low accuracy need for low dollars
and hi accuracy for hi dollars. Precision, or fine grained resolution, is inexpensive,
and you can transfer the accuracy from another temp probe to your machine and get repeatable results
without a temp standard built in.
This particular MSP430, for example, MSP430G2230IDR, has a nicely engineered diode temp sensor
inside, that can be switched in to one of its ADC channels to read the temperature of the chip.
The diode will have a small batch to batch random variation, but will always repeat very closely
as temperature differences happen. There is a temperature compensated volt reference for the
ADC so volts measured are truly accurate. Temperature repeatability of .01 deg C is probably
possible, although that's not accuracy, and would only agree that closely on long equilibration
soak times after a temperature change.
All you need is to put the chip in the stirred air you want to heat and you're accurate
to a very reasonable precision, and you could get better accuracy by calibration.
Repeatability and precision are easy to get with silicon microcontrollers.
That one I mention costs $46/qty 100, or 46 cents each and has four channels of 10 bit analog converter.
Is 0.1 degree C inherent reference standard accuracy necessary for incubation? No...
repeatability is nice, an easy cal feature is nice... Your code can have a mode where
when you press a calibrate button, it changes its look up tables to use what your external
fancy temp sensor reference standard says. The code could take input as up/down buttons
to adjust the temperature lookup table while controlling temp at 35 deg C. You would put the tip
of your hi res. platinum temp probe in the incubator for the calibration for a few minutes for each
up/down command until stable at 35.0 deg C. Then it will repeat, and be a transfer standard
for the cal thermometer for many months or years with as good accuracy and precision
as the cal thermometer even though it does not have an internal temp standard that
accurate. It does need a very stable, repeatable volt standard inside or on board, and
to make no changes to the chips used to keep its cal.
John
I want to watch RH for my incubators, this seems like the best option due to resistance to damage at 100% RH :
http://www.sparkfun.com/products/10167
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OK, that's a $10, $8 sensor. We had a $2.80 bill of materials going for this incubator so far...
You might want to use that if 92% RH was optimum and you needed that. But...
it's a little out of line price wise, so....
With an incubator that stirs air for even temperatures, it will have some flow of air you
can use to advantage to measure RH by definition. The definition is pretty much a differential
temperature between wet and dry with plenty of air flow over the wet especially since
max evaporation, ( as in swinging a wet bulb thermometer around and around for a while),
has some relation to temperature drop in various humidities, and you can create a look up table of
values to do the translation. So, in an incubator, you rig a diode voltage vs. temperature sensor
($0.25 for the first one, $0.11 for the second), for wet and dry using a 1N4007 diode
for each, (and ones from the same manufacturing batch), measured by and ADC channel
all coming from the 46 cent MSP430G2230IDR microcontroller I mentioned earlier, and referencing the same
precision voltage accuracy standard MSP430G2230 has built in, and you get the same result, accurate
rel. humidity, as you get with a $10 sensor.
The $2.80 and climbing bill of materials incubator version may lack some kind
of convenience feature the sensor has, but for incubation purposes, it will hold RH
and temperature rock steady if you have some kind of movable door to let air flow across
a wick into some distilled water, or not, by degrees, in a negative feedback control loop
via the code and the above mentioned measuring sensors and ADCs.
The bill of materials is climbing higher now since we have added more performance to
the requirements, but the system is set up for heaters, and controlling one more is easy,
so we can consider Ni-Ti springs as a wet/dry door mover and be climbing the performance
hill for cheap! All that's left is ways to make 3D shapes in water proof materials
inexpensively. Then you can make the swirl chamber for air flow, and wet dry areas
with a wick and H2O reservoir, and a snazzy outside look in 3D. How much would
that 3D enclosure cost?
For 3D enclosures, I've been thinking the well proven rapid prototype method of
ink jetted water/glue holding together starch could be good for some low volume
first articles -- you can harden starch with cyano-acrylate, (crazy glue). Or 3D
print the negative shape to get a mold, harden with cyano-acrylate, coat with something
for durability and mold release, and use it as a mold till it wears out and print another...
A good material for an incubator would be HDPE. For some shapes with low accuracy requirements,
your incremental cost of producing slow low pressure molded HDPE part of about 250 grams
could be (scrap price sm vol $2/kg) x.25kg + molding effort/costs $0.4 = $0.9.
That boosts the kit BOM total to maybe $4. (with a little mfrg infrastructure put in place)
John
John
when designing something like this, you have to ask yourself what will happen if a component fails or you have some bizarre software bug that will allow the heater to run non-stop.
I don't think needing to autoclave the incubator is really a good
idea, unless you're talking about it being pretty small. Sprayable
with ethanol or bleach without dissolving should be a pretty good rule
otherwise. Or maybe disposable.
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Anything with sitting water needs autoclaving after time.
On Mon, Apr 23, 2012 at 9:14 PM, Simon Quellen Field <sfi...@scitoys.com> wrote:
> So you can spray the shoelace with bleach.
> :-)
>
>For that matter, filling the humidifying tank with hydrogen peroxide
> instead of water would seem to also work fine. The wet bulb won't care
> if it is wet with peroxide instead of water.
>
That sounds like a good point for keeping the water clean, longer...
but at some point, life finds a way to get grimy
I'm just thinking of my combined incubator/centrifuge/liquid handler machine,
where the turntable for holding vials doubles as the fan.
Still, that reversing idea to change function might work in that setting also...
Hmmmm....
Yes, RH is hard to benefit from if it has to be sterile.
What need is that?
Instead, could you control RH enough in a vapor permeable vial that is soaking in the desired temperature
so as to decouple temp from humidity?
Otherwise you might as well call it a flow cabinet incubator with UV, HEPA filters, etc.
and it gets large and unwieldy.
Won't mold grow on a RH sensor too? How do you sterilize it?
Toss it out every month at $10 + installation swap out costs? Naahh...
Maybe UV, HEPA filters, etc *is* what you need. They could be small,
and keep the sterile zone separate from the RH sensor and keep it accurate
by maintaining a good flow around the through the filters.
Controlling RH and temp sounds complex. Probably will be starting with
a machine to process vials, rather than open dishes of culture needing
a warm humid breeze.
You could be pessimistic, imagining what is not.
I'm not thinking of any junk assemblages. Who mentioned any?
Sorry, my opinion is just that shoe strings and unnecessary buckets of
water is a bad option to take if you're trying to do biology, not
spend hours on something that will get grimy, or if the wick reservoir
spills.
Like I said, /I want RH control and sense/, this is not necessary for
doing a petri here or there, or an eppendorf of media.
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OK. It sounds like you're not suggesting how to make an incubator
in general, but a specific research experimental setup.
could you control RH enough in a vapor permeable covered
vial/dish/box that is soaking in the desired temperature
so as to decouple temp & RH from sterility?
> Now, let's look at ways to make cheap autoclavable humidity sensors <http://www.youtube.com/watch?v=Ui300HzoTOQ>.
http://www.johnsondiversey.com/Cultures/en-NZ/OpCo/Products+and+Systems/Categories/Wettex.htm
"Wettex Sponge Cloth is manufactured from a special blend of cotton, cellulose and salt. The cellulose provides excellent
absorbency whilst the salt is dissolved and rinsed away in the manufacturing process, leaving pores or hollows which improve the
high level of absorbency even further. "
So, is there some residual salt in Wettex sponge cloth?
I wonder how long it might stay calibrated?
Calibration is a good thing. You can make it easy if you put some work into
the code and the machine to be calibrated. It doesn't have to be a drag.
Really measuring things is the foundation of science.
I've heard about filtering things to sterilize them a few times
recently... is this a new thing? I don't recall it being possible to
do this when I worked in a lab way back when, but maybe it was and I
just never did it (or forgot). It seems like any filter small enough
to get viruses out would also impede airflow so much that you'd need a
tremendous pressure differential to get any throughput.
-Dan
And maybe hard to get humid air through without it getting wet and clogging?
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As to humidity control; I won't get into the mechanics, because it's not
something I know a great deal about. But, a cheap hack to avoid standing
water from getting contaminated is to add 1g/L CuSO4.7H20 (Blue Copper
Sulphate) to the water. Copper Sulphate is a pretty effective biocide,
so this tends to prevent anything growing in it.
However, reading through MSDSs one day, I discovered that copper
sulphate is considered "extremely toxic to the aquatic environment"; try
to avoid washing it down the sink. Just let it dry out and re-use if
possible after autoclaving.
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We grow mesophiles like E.coli at 37C because, for most of them, that's
the ceiling for comfortable growth. Higher temperatures mean more
reactions per second, meaning faster growth. However, any higher than
this ceiling, and heat-shock starts to get induced. While the cells will
survive, their gene expression profiles will change markedly.
So, if you and I set our incubators to 37C, and mine hits 36.5 while
yours hits 37.5, that could have a significant effect on our experiments
with the same DNA constructs. If any protein folding effects are
interrupted by heat-shock, you'll have reduced apparent expression. If
we're using heat or chemically induced promoters, you'll seem to have
higher expression at the same temperature.
At the very least, you'll have faster growth than I will at the same
apparent temperature, even controlling for all other factors.
If this were unavoidable I wouldn't complain, but for the difference of
�0.5, it's not worth skimping on accuracy. Science is about good
experimental control and reproducible results. If our equipment has such
significant error, you and I can't really compare or reproduce one
anothers' work; that's bad science.
On 24/04/12 00:23, Simon Quellen Field wrote:
> This is an incubator, guys.
> What organism do you know that maintains its temperature to 0.1C?
> Why would you think that was important for anything you are going to
> incubate?
>
> Let's suppose that you need to incubate something for 10 hours (600
> minutes).
> Suppose you set one incubator for 310 kelvin, and another for 310.1.
> Thus one is to get 186,000 degree minutes, and the other gets 186,060 degree
> minutes.
>
> You open them both, and immediately the air temperature changes by 11
> degrees
> to 26, the temperature of the Petri dishes full of agar.
>
> It takes both incubators 20 minutes to settle down to their set temperature.
> You have an average of 5 degrees below the set point during those 20
> minutes.
> That is 100 degree minutes off already, which is more than the 60 degree
> minutes
> by which the two incubators have been set.
>
> But more to the point, suppose we are incubating E. coli.
> Let's look at some of the protocols in
> One says to incubate at 37 Celsius for
> 18 to 24 hours. Another of
> them<http://www.neb.com/nebecomm/products_intl/productC2988.asp>says
> to expect a 2-fold loss
> of transformation for
> every 15 minutes that a 1 hour incubation at 37 Celsius. A
> third<http://openwetware.org/wiki/Maxiprep_of_plasmid_DNA_from_E.coli_protocol>calls
> for incubating
> at 37 Celsius for 30 minutes, then incubating 'at room temperature' for 10
> minutes.
>
> It does not look to me like anyone is calling for one tenth of a degree of
> accuracy in
> temperature. But more to the point, given that how long the cultures are
> incubating
> is so variable, being off by a couple degrees does not seem like it is
> going to make
> any difference.
>
> If it *does* make a difference, is temperature the right thing to be
> measuring?
> If the reason we incubate at 37 for an hour is to get a certain density of
> critters
> per milliliter, why not incubate until the optical density is some
> particular value?
>
> Maybe we shouldn't bother with electronics at all.
> Run some hot water from the tap and adjust the temperature to 37.
> Get a 5 gallon insulated beer cooler and fill it with water from that tap.
> Put your Petri dish in a zip-lock bag, set it in the water, and close the
> cooler lid.
> Take it out an hour later. The water temp is still 37.
>
> But that takes all the fun out of building the device. So let's use the
> device to
> do *sous vide* cooking, or to incubate chicken eggs (which will hatch in 21
> days
> even if you are off by 10 degrees). Your *sous vide* pork chop will come
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OK. That's a decent reason, but I maintain you can have your 0.1 deg C
without an absolute reference built into a bought part and escalating
bill of materials. It can be calibrated into
the complete system/instrument with a trustworthy reference standard of temperature.
And cal won't need to be done often. Planning to check calibration never
and trust a reference standard built into the machine would be bad science also.
John Griessen
But if I need a reference, and I only have one incubator, I'll still need to buy at least one good temp sensor. So I guess we should be talking about two designs, a reference or golden standard, and "slave" devices which get calibrated against that, as our lab needs grow
It's not the error in my own samples that matters, so much as the
variance between incubators. Also, it's not about the cells' survival;
it's about maintaining them at a known growth state.
We grow mesophiles like E.coli at 37C because, for most of them, that's
the ceiling for comfortable growth. Higher temperatures mean more
reactions per second, meaning faster growth. However, any higher than
this ceiling, and heat-shock starts to get induced. While the cells will
survive, their gene expression profiles will change markedly.
So, if you and I set our incubators to 37C, and mine hits 36.5 while
yours hits 37.5, that could have a significant effect on our experiments
with the same DNA constructs. If any protein folding effects are
interrupted by heat-shock, you'll have reduced apparent expression. If
we're using heat or chemically induced promoters, you'll seem to have
higher expression at the same temperature.
At the very least, you'll have faster growth than I will at the same
apparent temperature, even controlling for all other factors.
If this were unavoidable I wouldn't complain, but for the difference of
€0.5, it's not worth skimping on accuracy. Science is about good
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It's not the error in my own samples that matters, so much as the
variance between incubators. Also, it's not about the cells' survival;
it's about maintaining them at a known growth state.
We grow mesophiles like E.coli at 37C because, for most of them, that's
the ceiling for comfortable growth. Higher temperatures mean more
reactions per second, meaning faster growth. However, any higher than
this ceiling, and heat-shock starts to get induced. While the cells will
survive, their gene expression profiles will change markedly.
So, if you and I set our incubators to 37C, and mine hits 36.5 while
yours hits 37.5, that could have a significant effect on our experiments
with the same DNA constructs. If any protein folding effects are
interrupted by heat-shock, you'll have reduced apparent expression. If
we're using heat or chemically induced promoters, you'll seem to have
higher expression at the same temperature.
At the very least, you'll have faster growth than I will at the same
apparent temperature, even controlling for all other factors.
If this were unavoidable I wouldn't complain, but for the difference of
€0.5, it's not worth skimping on accuracy. Science is about good
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Well put Simon. My motivation in talking about calibration was indirectly
also about the idea of not focusing on just one criterion, but measuring,
like you are saying.
I'll be thinking of ways to make combo instruments that let you automate
more observations going on during any process involved.
On 04/24/2012 11:54 AM, Simon Quellen Field wrote:
> makes a great loaf of bread in the winter or the summer, because
> my protocol is not to measure the temperature and time accurately, but to knead
> it after the volume doubles.
I use a bread machine and it falls down on things like this. I've thought of
how small the market would be for an open bread machine with a light beam
dough rise sensor instead of a timer for when to knead many times as I got
small bricks instead of loaves of bread. Some extra ingredients change the speed
of rising -- winter or summer too. It would be a flop of a product, so few use
bread machines. Unless they don't use them because they're so hit and miss as they are now...
On 04/24/2012 11:58 AM, Simon Quellen Field wrote:
> Having an accurate thermometer in the lab is a good thing.
.
.
it can be used to set the
> calibration point of the incubator for each run, giving you some confidence
> that nothing has gone out of calibration in the incubator between runs or
> during cleaning.
Even frequent calibration can be easy if designed for. I can see a cal port
in the side the incubator machine that lets you put a temp probe there to
get good readings without cooling off or upsetting the system. A cal port
for a temp probe should be low on the machine so a probe resting on the lab
bench stays put with its end in the calibrate port. It might be a spring loaded
door with a notch for the temp probe, or it could be a simple plate of plastic
with a notch that users can file to fit, replace with generic material if lost,
and slides in a groove with no spring closer.
John
--
> On Tue, Apr 24, 2012 at 1:20 AM, Cathal Garvey <cathal...@gmail.com>
> wrote:
>> Higher temperatures mean more
>> reactions per second, meaning faster growth. However, any higher than
>> this ceiling, and heat-shock starts to get induced. While the cells will
>> survive, their gene expression profiles will change markedly.
What Cathal is saying here is a combination of things, that the temp
effects the growth rate so you could look at colony size delta with
vision processing or cell density with a light meter, but gene
expression IS heat dependent... when free energy levels are over a
protein or ribozyme's threshold (whatever that may be), stuff can
happen in a marked way (i.e. HSPs)
Yes, you fit its curve at one point to calibrate. If using a look up table,
that means recalculating all the values adjacent to the new zeroed in value
at the thermometer temp according to the transfer function so
they'll be ready to use.
But in chemistry reactions are directly related to temperature, so its not really a proxy
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