Teardown Tuesday: Radar Gun

In this Teardown Tuesday, we are going to take a look at the inner workings of a radar gun!

If you're a speeder or a sports player, you may have experience with one of these! Radar guns are used everywhere from law enforcement to sports. 

The Bushnell Velocity Speed Gun

In this Teardown Tuesday, we are going to take a look at the inner workings of a radar gun that is intended for sports. This is a Bushnell Velocity Speed Gun that operates on 24GHz (K-Band).

Opening It Up

The opened up radar gun

Opening up this radar gun was easy! There were eight standard-sized Phillips screws holding its casing together. With the screws removed, the two-sided enclosure simply pulled apart. The with the shell open, the radar horn, trigger switch, and three PCBs are revealed!

Circuit Boards

There are three circuit boards inside of the radar gun. They are labeled "Filter Board", "Digital Board", and "Trigger Board". These are connected through a pair of five-conductor Youngshin AWM 2896 ribbon cables. These cables are about 50mm long and can be used at voltages up to 30V.

The Youngshin ribbon cable

The filter board is mounted to the radar horn via four machine screws. This two-layer board contains a “pre-amp” board, a few surface mount ICs, and a large inductor.

The filter PCB

The pre-amp board is soldered onto the filter board. It contains the K-Band transceiver, a few passive components, and two transistors. The bottom layer of this PCB is a large ground plane. A ground plane also covers a large portion of the top layer of the PCB.

The pre-amp PCB

The digital board contains the ‘brains’ of the radar gun, a TI microcontroller (more on that later).
The board also contains the power supply and LCD. Additionally, this circuit board contains several unpopulated components and a programming header.

The digital PCB

There is not a lot on the trigger board, only a positive battery terminal and the spring switch for the trigger.

The trigger PCB

Radar Horn

The radar horn

In order to receive the radar signals, the radar gun relies on a relatively large radar horn. The horn appears to be cast zinc that is coated with a chromate conversion coating, giving it a gold appearance. The radar horn has places for six machine screws and two indexing pins for the radar transceiver.

Radar Transceiver

\

The MACOM radar transceiver

In order to emit and receive, the radar gun relies on a K-band transceiver. This transceiver is manufactured by MACOM, part number MACS-007801 (PDF). This transceiver operates at 24.100GHz to 24.150GHz and has an output power of 5mW.

Inside of this die-cast package, there is a Gunn diode oscillator and Schottky diode. According to MACOM’s datasheet (see the link above), the intended applications for this transceiver include police radar and presence-sensing applications. Below is the functional block diagram of this component.

The block diagram of the transceiver

Microcontroller

Controlling all of the functions of this radar gun is a Texas Instruments MSP430F413IPM microcontroller. This microcontroller is in an LQFP-64 package and is intended for application where analog signal processing is required.

According to TI, the built-in comparator and timer make this microcontroller ideal for industrial meters, counter applications, and handheld meters.

The Ti MSP430 microcontroller

LCD Display

The LCD

This radar gun uses a large custom segmented LCD display. This display is controlled through an 11-pin interface and contains 25 segments. There are 21 segments for the large numbers, a “Transmit” indicator, an “MPH” indicator, a “KMH” indicator, and a low battery indicator.

The LCD on

 

Radar guns are some of the few devices a consumer can purchase that rely on a radar. The radar transceiver and antenna can be costly due to the fact that devices likes these are often relatively expensive.

Thanks for taking a look at this Teardown Tuesday! Stop by next week for another teardown.