Team:Rotterdam HR/Hardware Temperature Controller
Temperature Controller
Hardware: Temperature Controller
The idea
To make sure the only thing influencing the gas production from the bacteria is the amount of carbon monoxide, we wanted to make a temperature controller. This will keep the temperature stable independent of the temperature outside the system (within a reasonable range, ±70 degrees Celius of target temperature). To achieve this, we used a peltier element with a control system of our own design.
Architecture
Building a complex system like a temperature controller is easier said than done. So, we first designed the architecture of the system, thereby dividing the system into smaller parts and the interfaces between these parts. These parts can then be designed individually, as long as you keep their interfaces in mind, and be assembled afterwards.
Peltier element
The first step was selecting 
the Peltier element, since all other parameters of the design depend on the
specifications of this element. But first, what is a Peltier element? A Peltier element is a semiconductor that
conducts heat from one side of it self to the other. It basically moves thermal energy when a voltage is applied
and a current can flow through it. The Peltier element needs energy to move the thermal energy, the energy it
needs is electrical energy. A side effect of this behaviour is that it also generates its own heat on the "hot"
side. We say "hot" side because when the direction of the current to the Peltier element is changed, so will the
hot and cold side of the Peltier element change.
We selected an element that is capable 
of moving a 150 watts of thermal energy, the TEC1-12715(seen on the first
picture connected to a heatsink). To work at full power, it requires 15 Amps at 15 Volts. This means it will also
produce 225 watts(15 Volts x 15 Amps) of thermal energy. The combined thermal energy that will be produced at the
hot side is 375 watts. This 375 watts of power needs to be dissipated, this means that when you’re cooling the
test tube, you also have to cool the hot side of the Peltier element. The second picture is the heatsink that
will be connected to the "hot" side of the Peltier element.
Power supply
Because the system will use over 225 watts, we used a standard PC power supply. Because designing a power supply
ourselves would be an entire project on its own. And in the theme of iGEM this would bring no significant value
to the table.
These PC power supplies can deliver this amount of power easily, albeit at 12 Volts. It also has built-in 3.3 and
5 Volt power supplies, which we use to power the logic of our controller.
DC-DC Converter
But how do we get 15 Volts from 12 Volts? For this purpose, we designed a DC-DC boost converter using the
TPS43061. This will convert 12V at 18.75A to 15V at 15A.
A DC-DC converter is a power converter most commonly found in power supplies and phone and/or laptop chargers. We
made a boost converter this means it will boost the input voltage to either a set or adjustable higher voltage
level.
Temperature sensors
To measure the the internal and external 
temperature of the case we needed something to measure
with.
For this we choose the DS18B10, which is a digital temperature sensor with a measuring range from -55°C to
125°C.
The temperature sensor is a necessary component in any temperature controller, because you first need to know
whether the temperature needs to be adjusted in the first place.
Fan control
As we cool the environment of the bacteria down, by transporting the heat from this environment to the outside environment, we need to dissipate this heat. We achieve this by thermally connecting a heatsink to the opposite side of the Peltier element. Passive cooling alone will not suffice, so we needed a fan to actively dissipate this heat and hooked it up to the heatsink. The first picture shows the fan connected to our own designed and 3d-printed case and added heatsink. With the casing closed, the air can flow nicely through the heatsink, this will add to it's cooling capabilities.