Attempting to build warm stage for microscope - New to Arduino/electronics

Hey all,

I am trying to make a warm stage for an inverted microscope - basically its a method to keep live cell samples at body temperature (37C) whilst running assays. I plan to use an LM35 and two heat pads from Sparkfun (with MOSFET) to supply the heat. Im hoping the LM35 will be suitable to measure temp accurately enough and switch on/off the pads in response to correct temp. I aim to work in temps between 35C and 45C.

Full disclosure: totally new to arduino (have run through some of the basic tutorials) and electronics in general. I'm a scientist by training (parasitology), but fond of taking a McGyver approach to save costs - basically we don't have the £10,000+ to buy a professional temp controlled stage/chamber. I had been reading up on many of the brewing solutions for temp controlling, but would really like to keep it as simple as possible.

Cheers

You may encounter problems with delays, because the temperature of the probe will increase or decrease slowly, not immediately when the heaters are switched on/off. The placement of the sensor is important, so that it will reflect the temperature of the probe, not that of the heaters or other material.

Eventually you can use two temperature sensors, to measure both the temperature of the heaters and the probe. In the best case you'll get a somewhat constant difference between the heater and probe temperature, so that you can increase/decrease the heater temperature by the difference of the actual and intended temperature of the probe.

Please provide an sketch of your intended device, with the placement of the heaters and sensors, and which materials are used between the heaters and the probe.

Hej DrDeitrich, thanks for the response. I’ve uploaded my rough schematic - had thought about wrapping the slide holder with the pads (as they are flexible), but as the xy stage was “misplaced”, the slide holder is manually moved around and would eventually damage the pad. So the idea is to make a small(ish) box (25cmx35cmx10cm) and suspend the two pads from the top. The LM35 will be near the biochip and the pads would then heat the air inside the box. Humidity is not an issue as the biochip is closed and the media is pumped over my cells.

If I had a way of being convinced that wrapping the slide holder was better, that would be the easiest way to do it, but just not sure i can control the temp as easily as heating the air, but if anyone has suggestion, they are greatly appreciated.

Cheers

Bump

Hi, I can't understand your schematic, perhaps it is not being rendered correctly on my phone. I see nothing labelled, for example.

What about a ds18b20 temp sensor? These are digital, pre-calibrated and are available in stainless steel probes, which could be submerged into your "media" (whatever that is... liquid/gel?)

Paul

Hi, I can't understand your schematic, perhaps it is not being rendered correctly on my phone. I see nothing labelled, for example.

Paul
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Hi Paul, not sure why the labels arent showing...

The temp sensor is not submerged in liquid. I want to heat the air in the box that will surround the stage/biochip - essentially a smaller version of the larger commercially available microscope incubators which are crazy expensive.

I think, like others said before, the biggest problem is that when it takes 2 to 3 minutes for the temp sensor to reach the ambient air temperature, the temperature inside the incubator could get notably higher than intended before the heating pad(s) are switched off.

I would use two temp sensors (as DrDietrich already suggested), one measuring the temperature of the heating pads and the other to measure the temperature inside the incubator. The idea here is to limit the heating of the heating-pads so that their temperature does'n exceed for example 40C. If the temp of the incubator would not get high enough with that setting, the pad temperature could be adjusted with a potentiometer. The code could of course be written so that it adjusts the heating pad temperature automatically with no need for a pot - but thats beyond my capabilities, I'd use the potentiometer.

Could it be better to measure the temperature of the biochip instead of the ambient air? Or the temperature of the media pumped on the cells? The latter would give the advantage of a much faster sensor response. And furthermore, should you heat the media instead of the air?

I would use the DS18B20 temp sensors, they are inexpensive, very accurate and there is no need to calculate the temperature value from voltage, you get the temp directly in centigrades.

The heaters don't need to be controled with a crude on/off. You can PWM them and have sketch adjust the duty cycle to maintain the desired temperature. The problem will still be the lag between changing the duty cycle and the resulting change in temperature.

GardenElf:
I would use two temp sensors (as DrDietrich already suggested), one measuring the temperature of the heating pads and the other to measure the temperature inside the incubator. The idea here is to limit the heating of the heating-pads so that their temperature does'n exceed for example 40C. If the temp of the incubator would not get high enough with that setting, the pad temperature could be adjusted with a potentiometer. The code could of course be written so that it adjusts the heating pad temperature automatically with no need for a pot - but thats beyond my capabilities, I'd use the potentiometer.

I'm trying to keep it simple as I am learning as i go with this stuff and had though 1 sensor was easier than 2.

Could it be better to measure the temperature of the biochip instead of the ambient air? Or the temperature of the media pumped on the cells? The latter would give the advantage of a much faster sensor response. And furthermore, should you heat the media instead of the air?

The chip not very big (2cmx2.5cm) it seemed easier to measure the air in the box. I basically want to make a smaller, cheaper version of this (for example http://www.wpi-europe.com/products/microscopes-and-cameras/miscellaneous/microscope-incubators.aspx). The chip is designed for micro volumes, so its not feasible to warm the media directly. The media is kept at 37C, but the samples we use are field isolates and have limited supply, therefore we only use 120ul maximum. So once the sample is added to the chip, it would start to cool. our current solution is a halogen bulb/hair dryer combo which doesn't exactly give us any fine control...

I would use the DS18B20 temp sensors, they are inexpensive, very accurate and there is no need to calculate the temperature value from voltage, you get the temp directly in centigrades.

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