Drug Preservation Device

I. Executive Summary

In order to maintain the quality of prescription medicines, we designed and created a device that will sense and regulate the temperature and humidity of medicines as well as notify users if they have been exposed to dangerous conditions. In this report we will discuss the full problem we are trying to address, design alternatives we have considered, the design we ultimately chose, as well as the results of our device. The device uses a DHT22 to sense the temperature and humidity of the enclosed medicine and allows for an Arduino Nano 33 IoT to process the signals. If the medicine is reaching a critical temperature (10°C to 30°C is the optimal range), it triggers the H-bridge to change the polarity of the thermoelectric cooler to either heat or cool the device, depending on what's required. Whenever the temperature or humidity becomes too extreme (above 60% humidity or outside of the optimal temperature range), the Arduino will use its wifi capabilities to send a push notification to the user. Another backup notification system is used with LEDs but will be further discussed in the Design Selection section. Our device meets all the objectives requested by our client with the exception of continuous heating and cooling for 48 hours. It accurately senses temperature and humidity even at extreme temperatures (between -10°C and 50°C) and promptly alerts users if their medicine is being exposed to unfavorable conditions. It is portable and convenient for users of all ages who must take prescription medications.

​

II. Introduction and Problem Statement

When designing the Drug Preservation Device, the client stated that the device has to be able to fit inside a typical car cup holder and use a car battery for power without draining it for at least two days. There was also emphasis on designing the device to be affordable, or at least compared to similar products on the market. Additionally, to make the product easily marketed, it had to be aesthetically appealing and preferably black. The client also requested that the device be user friendly and safe, which meant the device would have to have sensors to notify the user if their medication was exposed to undesired conditions and be somewhat childproof to prevent accidents. The last thing the client requested of the design is that it be durable so users can rely on it and not have to worry about frequent replacements.

Based on the clients requests, we formed the problem statement: the goal is to design a device to preserve drug quality in unpredictable car temperatures to provide convenience for people who take daily medications. In order to achieve this goal, a few objectives were outlined. The first objective the device should fulfill is marketability and the metrics used to measure it are that the device costs less than $60 and is dark in color. The product also has to have an interior space that can store a cylindrical medicine container measuring up to 20mm in diameter and 75mm in length. Portability is also a key objective for user convenience so the entire device must fit snugly into a standard car cup holder and have a maximum height of around 22cm. The next objective the device needs to fulfill is to have a temperature regulating system. This system must heat/cool medicine to between 20°C and 25°C within 3-5 minutes after the device is turned on. After the initial temperature of the medicine is within the initial desired 20°C to 25°C range, the temperature regulating system must continue to heat/cool the medicine as needed in order to keep the medicines within the safe range of 10°C to 30°C. Similar to the temperature regulating system, there must also be a humidity regulation system. This system must ensure the humidity of the prescription drugs remains under 60% after the initial five minute period.

However, in case the medicines are exposed to unsafe temperatures or humidity, there must also be an indicator/failsafe system that will alert the user. Users must be notified if their medicines reach outside the desired 10°C to 30°C temperature range or are exposed to humidity greater than 60%. The device must be able to function accurately and measure correct temperature and humidity values even at -10°C or 50°C. The device must be powered by a standard 12-volt car battery and last up to 48 hours (max current of 1 amp for 48 hours straight) without draining it. The final three objectives are durability, reliability, and water resistance. We will determine durability by ensuring the product can withstand at least 100 drops from four feet (because the device will be used in a car). Reliability will be measured by ensuring the device functions accurately for at least 1000 uses. A standard use is defined by unscrewing the lid of the device and then screwing it back on and powering the device on for temperature and humidity regulation. Lastly, water resistance means there must be no exposed electrical components and it must be able to withstand common cleaning products. Additionally, there are a few constraints that must be considered. The design must be completed before December 10, 2021 and cost less than $300 to produce a prototype. The completed device must also be safe and therefore pass the IEC 60601 Medical Safety Test. This medical safety test is conducted by representatives who verify medical device’s integrity for at home use.

​

III. Design Alternatives Considered

The first function addressed was measuring temperature and measuring humidity. A few means considered were thermometers, infrared sensors, thermocouples, different temperature sensors such as DHT22 and TMP36, and humidity indicator cards. Another big function that required possible design alternatives was an indicator/fail safe system that could alert users that their medicines were exposed to high humidity and extreme temperatures. Different means discussed were LEDs, a buzzer, LCD screen, and phone notifications through a Wifi enabled microcontroller. For the function of storage, we discussed variations of aluminum capsules, a copper pipe, a pill bottle, and 3D printed inserts. To regulate temperature through heating and cooling we discussed fans, a heating lamp, steam, and thermoelectric coolers. To regulate humidity, we considered silica gel packets, baking soda, a sponge, and a dehumidifier. For the function of power, we considered a few alternatives/additional options to the client requested battery power. We discussed using a DC battery, solar power, and miniature windmills. A few other design alternatives were considered for the functions of durability, portability, safety, and water resistance and Appendix A has a complete outline of all these functions, means, and specifications.

​

IV. Basis for Design Selection

The biggest decision we had to make was in regards to the temperature regulation system. We found that thermoelectric coolers were the best means to both heat and cool the drugs when needed. In an attempt to save space and keep the device portable, we opted to use one TEC1-12706 thermoelectric cooler rather than two and use an L298N H-bridge to reverse the polarity of it. Our initial model was successful and the results are included in Appendix B. Similarly, with the goal of saving space and current draw we opted to use a DHT22 as our only temperature and humidity sensor because it combines both functions into one mean. We also decided to use silica gel packets to absorb humidity because they are small, effective, and really cheap and easy for customers to replace if ever needed.

Deciding on the enclosure components was just as important. We decided to 3D print the exterior of the device out of black ABS because it is a great insulator and will keep the internal temperature of the device more stable in extreme conditions. The SolidWorks assembly drawing is included in Appendix C. Additionally, it met the client's desire for having a black exterior and isn’t expensive to manufacture. The interior however needed to be conductive in order to allow for the regulation of its temperature and 3D printing with metal filament is much more time consuming and expensive. Therefore, we opted for an aluminum capsule to act as the interior because the conductive walls allow for proper temperature regulation and it came with a screw on lid which acts as an added safety feature.

Another key component during the design selection process was deciding on the indicator system that notifies users when their prescription medicines have been exposed to harmful conditions. We decided on using an Arduino Nano 33 IoT microcontroller with wifi capabilities. The wifi capabilities allowed us to write code that will send push notifications to users when their medicines are being exposed to these undesired conditions (see Appendix D for the link to our full code). Enabling push notifications is key for our device since it instantaneously notifies users and they will have the chance to get their medicines from the car before it is too late and they are no longer safe/effective. However, since not all users have a smartphone to receive push notifications and devices may not always be connected to wifi, we included an LED system for backup notifications. We included three LEDs: a green one to signal the device is powered on and functioning, a blue one to signal that the humidity is getting to an alarming level and the silica gel packet must be switched out for a new one, and a red one to signal that the medication has been exposed to either temperature or humidity levels that have impacted the medicine.

The last major design selection we made was to include a 9-volt battery as an additional source of power for the L298N H-bridge. While the device is mainly powered by a standard 12-volt car battery, the Arduino Nano 33 IoT only has a 3.3-volt output pin. The L298N H-bridge requires at least 7.5-volts to function, so an additional voltage supply is required to keep the TEC1-12706 thermoelectric cooler functional. A completed Bill of Materials and circuit layout diagram are included in Appendix E and Appendix F, respectively.

​

V. Evaluation of Results

To evaluate the integrity of our device and test if the DHT22 sensor was correctly calibrated, we ran five trials in different temperature conditions. We chose to focus on temperature testing rather than humidity testing because we know that silica gel packets are effective at absorbing moisture. We placed the device in a range of extreme temperatures that ranged from 6.3 degrees Celsius to 84.4 degrees Celsius using a combination of a heat gun and a freezer. Both internal and external device temperatures were then measured with an infrared thermometer and recorded below in Table 1 and displayed in Figure 1 for further analysis.

​

​

​

​

​

​

​

​

​

From the Internal Temp. and DHT22 Reading columns in Table 1 we can see that the DHT accurately senses temperature even at extreme temperatures. In Figure 1 we see that as the temperatures get more extreme the DHT becomes slightly less accurate, but is never more than 0.4 degrees Celcius off. This reassures us that the sensor is correctly calibrated. Similarly, from the External Temp. and Internal Temp. columns in Table 1 we see that even when the device is exposed to harsh temperatures, the interior of the device, and therefore the drugs, remain within safe conditions. These test results confirm the devices integrity and indicate that the metrics concerning temperature regulation are met.

Other metrics that are met by our design include being black in color, fitting into a standard cup holder, and being less than 22cm in overall height. Users are also notified through two different means. Push notifications are sent to users instantaneously when their drugs are exposed to harmful conditions and for those that do not have smartphones or incase of no wifi connection, there is a failsafe LED indicator system to inform users when their device is powered, in need of a new silica gel packet, or was unsuccessful in properly regulating their drugs. The interior aluminum capsule is 89mm tall and 38mm in diameter so it fulfills the metric and the clients request to have an interior large enough for most prescription drugs. The completed prototype has no exposed electrical components and has withstood common cleaning products such as Lysol wipes and is therefore properly water resistant. The device also withstood one hundred drops from four feet, meeting the durability objective. In addition to meeting many of the objectives, we also met two of the constraints we faced. The prototype was completed before December 10, 2021 and it cost less than $300 to produce.

As with all prototype projects, we have established a few design changes to propose for future production based on testing and evaluation. Our current notification system is fully functional for all users who download the IF This Then That (IFTTT) application and sign in to a specific account. In order to make this specification available to all future users, we would suggest designing an app that functions the same but is available to all users without a specific account login. Additionally, we would like to improve the enclosure by adding a feature to secure the silica gel packet rather than just placing it into the interior as it is right now. This would make the device more secure and prevent the silica packet from just falling out. Another structural change we propose to make is adding a switch for the nine volt battery powering the H-bridge. From our temperature testing results in Table 1 we learned that the enclosure is very well insulated so the H-bridge and thermoelectric cooler only need to be powered for short periods of time, if at all. The H-bridge has a total power dissipation of 25 Watts (per the data sheet) and therefore an average power consumption of 1 kWh. A fully charged 9-volt battery can supply 2.5 kWh so after 2.5 hours of usage, a new 9-volt battery is needed to keep the temperature regulation system functional. We estimate that the thermoelectric cooler only needs to be powered for five minutes every hour. This means the H-bridge only needs to consume at most 0.083 kWh and only after 30 hours of usage a new battery is needed. By adding a switch, the device would be able to function 1,200% longer than currently.

A few other objectives/constraints we weren’t able to fully meet are child safety, medical safety, and reliability. While our prototype features a screw on lid that provides some safety, we propose altering the lid to be fully child proof. In regards to medical safety, we believe our device would pass the IEC 60601 Medical Safety Test however this certification requires a certified professional to inspect the device and give the official approval. Before mass production, we suggest attaining this certification. Similarly, we anticipate the prototype's reliability since we believe the device will function accurately for at least 1000 uses, where each use is defined by opening the device and leaving the medicine exposed for up to five minutes to the outside environment and then powering it on for temperature and humidity regulation. However, the device must be tested 1000 times in a variety of environmental conditions to be fully confident in meeting this metric. Lastly, the current material cost for the prototype is $82.50 and could therefore not be sold for the clients requested $60 with a profit. We do anticipate mass production will severely decrease the material cost as parts will be bought in bulk and therefore we do not suggest compromising the devices integrity in exchange for using cheaper materials such as 3D printing filament that is weaker than ABS.

​

VI. Appendix

​