Temperature Controlled Box – Hardware

During the design phase of this project, we experimented with several ideas about most aspects of the project. Once we agreed about designing a temperature regulator, we knew fairly early on that we were going to use a hair dryer as our heat source, as the magnitude of hot air would be extremely effective for such a small enclosure. This proved to be the case once the project entered the testing phase.

 

The cold source, however, took a bit more planning. Our first design consisted of a small thermos filled with an ice bath with tubing placed directly over the water, with the other end inserted in the control room, with a fan somewhere in the middle. This design was abandoned fairly early due to multiple issues, primarily the moisture concern and building complexity of the model. Additionally, we were concerned that the effective cooling of this system would be insufficient. Our final design was much simpler to construct and proved to be effective enough for our purposes. We would house several ice packs in a wooden box that would sit directly next to the control room, with the fan directly between the two. The input/output holes were placed near the top and bottom of the reservoir on opposite sides, as to allow maximum air exposure to the ice packs.

 

Moving on the circuitry of the system, we utilized the temperature sensor and LCD screen of the A3BU, as well as the following pins, whose functions are summarized:

 

J1_VCC – Cold Reservoir Fan Power / Potentiometer Power

J1_TxD – NPN Transistor Base

J1_SDA – Blue LED

J1_SCL – Red LED/Relay Switch

J2_ADC1 – Potentiometer Sensor

J2_GND – Ground

 

The circuit runs in three different modes – off, heat, and cold. In all modes, VCC and ADC1 are constantly active, in order to figure out the desired temperature based off the resistance of the potentiometer. Off occurs when no other pins are active, and the actual temperature equals the desired temperature. The desired temperature is changed by rotating the potentiometer dial, which signals to ADC1. When the desired temperature is greater, SCL activates which both switches the relay outlets (turning on the hair dryer), and the red LED is powered on, indicating that the system is in heat mode. When the desired temperature is less, both TxD and SDA come on. TxD enables flow through the transistor, allowing VCC to power the fan, and SDA powers the blue LED, indicating cold mode. Once obtaining a desired temperature, the system will not rerun a heat or cold mode until the actual temperature drops below or rises above 2 degrees of the ideal (assuming the ideal temperature had remained constant).This circuit can be viewed in full in the schematic.