What's inside a Bluetooth-enabled breathalyzer?
The breathalyzer ready for use. Image courtesy of Amazon.
Opening It Up!
After checking to see if it actually works (you know, for science) it was time to open the breathalyzer. The breathalyzer was simply opened by removing two small Phillips head screws. The plastic shell could then be separated revealing the electronics inside of this compact device.
The breathalyzer exposed!
Circuit Board
The top of the breathalyzer’s circuit board
The PCB in this breathalyzer is very small. On the top of the PCB, there are many of the large components, such as the Bluetooth module and the power supply for the inductor. This PCB contains surface mount and through hole components on both sides of the PCB.
The PCB is a two-layer board with green solder mask and white silkscreen on both sides. The bottom of this PCB contains the microcontroller and many other small surface mount components.
The bottom of the breathalyzer’s circuit board
Microcontroller
The 8051-based Silicon Labs microcontroller
At the heart of this breathalyzer, there is a Silicon Labs C8051F850 microcontroller. This microcontroller is in a 20-pin VFQFN exposed pad package and is based around an 8051 core. The 12-bit ADC inside of this microcontroller is used to read the voltage from the sensor.
Bluetooth Module
The punch through designs Bluetooth module
In order to send data back to the smartphone application, this device uses a precertified Bluetooth module. The Bluetooth module used is manufactured by Punch Through Designs, part number LBM313.
This Bluetooth module is designed to be very low powered. Punch Trough Designs intends for this module to be used in various mobile accessories such as health monitors.
An interesting note is that this Bluetooth module is also used on the LightBlue Bean development board.
Alcohol Sensor
The alcohol sensor
According to BACTrack, this device relies on a sensor that is ‘semiconductor’ based. The sensor is a metal can package with three leads coming out of it.
Inside of this package, there is a heating element and a sensing resistor. The heater requires a fair amount of power, over 100mW. There are no part numbers or other identifying features on this sensor.
Does it work?
Typically police and certified breathalyzers cost 100s and even 1000s of dollars. So how does a $40 breathalyzer stack up? Let's find out!
Let's test it out! Image courtesy of Amazon.
In short, this breathalyzer gave erratic results. While completely sober and waiting the recommended 15-minute period after eating or drinking, the device produced results that ranged from a 0.010 BAC to a 0.029 BAC over several sequential tests.
After several drinks and the waiting period, this device produced results from 0.000 BAC to a 0.059 BAC. While I didn’t have a calibrated breathalyzer to compare to, the sequential test results varied. An interesting note is that in this product's literature it lists that this device “estimates”.
Image courtesy of Amazon.
Tons of consumer electronics are Bluetooth-enabled and the number grows every day. Many of these devices use a pre-certified Bluetooth module for cost savings. There are several other teardowns on All About Circuits that show this to be the case:
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