Teardown Tuesday: What’s inside a Bluetooth Radar Detector?March 22, 2016 by Alex Udanis
Ever wonder what's inside a radar detector? In this week's Teardown Tuesday you'll find out!
In this Teardown Tuesday, we're going to take a look inside of a radar detector! We are going to look at a Cobra iRad 500, this radar detector is unique in the fact that is designed to pair with a cell phone's Bluetooth connection and have the phone display various alerts as opposed to a display on the device. When this radar detector originally came out its MSRP was $130.
Inside of this radar detector's relatively simple package, there are a lot of electronics! For example, there are 4 separate circuit boards, around 25 screws, and +10 IC’s. It didn’t take much to open up this radar detector, I removed four Phillips screws and it was open. The electronic components came out in a very nice module that can be seen below.
The electronics in the radar detector
On the bottom of the electronics, a the main microcontroller can be seen. An interesting observation is that the female header, that can be seen by the ARM microcontroller, protrudes from the bottom of the plastic enclosure and is then covered by the FCC ID label.
The bottom of the main circuit board
The top of the radar horn
The big star of any radar detector is its wave guide or ‘radar horn’. The radar horn is used to direct radar waves to the detection circuitry. After taking out even more screws, the radar horn comes apart into two sections revealing a circuit board.
The radar detection circuitry
This board contains the Superheterodyne receiver that is used to detect 3 bands of radar; X band (8 to 12GHz), K band (18 to 27GHz) and Ka band (27 to 40Ghz). This circuit board contains gold traces as opposed to the typical copper ones. Additionally, this circuit board is made with a special substrate intended for RF applications.
The secondary board on the bottom of the radar horn
Attached to the bottom of the radar horn is another circuit board. This secondary circuit board amplifies and processes the signal detected by the receiver. The two circuit boards are connected to each other through 4 pins that were soldered into place. The radar horn assembly connects to the main board through a 2x4 header pin. These circuit boards were de-soldered and can be seen in the image below.
Both circuit boards in the radar horn.
The dual linear regulators
Due to the radar detector's application of being always plugged in, the device employs several linear regulators to achieve the voltage supply rails that the electronics inside need to function. The device uses two 7800 series linear voltage regulators to generate a 5v and an 8v rail. Additionally, a third regular smaller regulator is used create a 3.3v rail.
The Bluetooth module
One of the unique features of this particular radar detector is the in the inclusion of a Bluetooth module to send data to a smartphone equipped with the iRadar app. At the heart of the Bluetooth module is a CSR BC417143B Bluetooth SOC. This IC is designed to reduce the part count that is needed when implementing a Bluetooth radio.
The Bluetooth IC
The top of the circuit board has several IC's and passives on it, the bottom of the circuit board also contains circuitry. Taking up most of the real estate on the bottom of the Bluetooth module is an MX29LV800T flash memory module made by Macronix International.
The flash memory IC
Another interesting aspect of this radar detector's design is the amount of components that were included in order to produce the sound effects. The first component is a speech synthesizer, originally this part was made by OKI Semiconductor. In 2011, OKI changed its name to Lapis Semiconductor. The radar detector uses an IC labeled L22422. This is very similar to the Lapis Semiconductor ML22420. An interesting note is that both that the ML22420 and L22422 have built-in audio drivers for speakers up to 8 ohm. This radar detector uses a separate audio amplifier to power it's 8 ohm speaker.
The audio synthesizer and serial flash
Paired to the speech synthesizer is a 16M-Bit serial flash, Macronix MX25L1606E that contains all of the audio clips that the radar detector produces. The audio synthesizer takes and uses the data from the flash memory to produce the sound effects. The audio signal from the voice synthesizer is then passed onto an amplifier that powers the speaker inside of the radar detector.
The audio amplifier and supporting circuitry
Due to the radar detector's application of being in a car with other sources of noise, its audio has to be loud. The dedicated amplifier IC drives an 8 ohm speaker. At max volume, the speaker is surprisingly loud for its size.
The speaker on the radar detector
Wrapping It Up
There's a lot more to this radar detector that wasn't mentioned in the article. Including the two lenses that direct the IR light from LIDAR guns into photodiodes. The photodiodes detect the pulses that LIDAR guns use to determine the speed of a vehicle.
Also worth a mention is that an ST STM32F100R8T6B Cortex-M3 microcontroller powers the entire device. This is a 32-bit microcontroller that can run up 24MHz.
There are numerous different types of radar detectors available, but the design of this detector is pretty typical. Some variations on this design include dual radar horns, GPS modules, and color screens.
Thanks for looking at this week's Teardown Tuesday. Stop by next Tuesday for another teardown!
We're always looking for new things to teardown, if you have any suggestions or would like to contribute an item for a future Teardown Tuesday click here for my email address.
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