The main electrical component used in the pacifier is the RFduino microcontroller. Similar to a standard Arduino, the RFduino can be programmed using Arduino software, which provides students with a familiar platform and coding language. The benefit of using the RFduino is its small size, built-in Bluetooth capabilities, and the availability of both prototyping and surface mount versions of the chip.
The next three components included in the design were sensors to monitor temperature and breathing rate, as well as a luminometer to measure light produced by Luciferase.
Both the temperature and breathing rate were monitored using small NTC thermistors. The thermistors were then used in voltage divider circuits to monitor the changes in resistivity through an analog input on the microcontroller. One thermistor is placed in the tip of the nipple to monitor temperature, and the other placed underneath the child’s nose to detect changes in temperature corresponding to their breathing.
The luminometer was constructed using a light to frequency sensor (TSL237T) which has the ability to detect individual photons as they come in contact with the sensor. By counting photons over a set period of time, a rate can be calculated to measure the amount of light in an enclosed environment. To detect such small amounts of light, the sample must be isolated in a dark container for these measurements.
Additional hardware components included in the final design were a battery holder for a 3V coin cell battery, a switch to turn the pacifier on and off, and a location to connect the RFduino microcontroller to a desktop computer so that it could be properly programmed. The final schematic for the hardware design is shown below.
To include all the required components in the pacifier, a printed circuit board (PCB) was designed using EagleCAD. Due to such limited size constraints, surface mount components were used where possible. This allowed for both sides of the board to be used so that the components could overlap and reduce the amount of space required. Since both sides of the board were used, the layout of the components was also designed such that anything that needed to be accessible (light to frequency sensor, connections to the RFduino, on/off switch, and battery holder) were placed on the top of the board. All remaining components were placed on the bottom so that users could not access them or interfere with the wiring. A single hole was also drilled in the board so that it could be attached with a screw to the back half of the pacifier casing. Any additional wire connections, such as those required for the thermistors, could then be contained between the bottom of the board and the back of the casing.
The EagleCAD layout of the PCB and the completed board are shown below.