Radar gun build
STEP 1: MATERIALS
Arduino Microcontroller
The A B USB cable
seven segment led displays
I am using LTS-4802BJR-H1 seven segment displaysHC-SR04
Ultra sonic sensor
Solder+Soldering iron
Printed board to solder toWiresResistors
2 resistors between 330 ohm and 1000 ohm.

STEP 2: THE CIRCUIT DESIGN

I recommend to make the circuit first on a bread board so as to test and make sure your equipment works.

1. Plug the HC-SR04 sensor into a bread board and make sure that the pins are not in the same column.

2. Put in your seven segment displays and pay attention to the orientation that is required so that each pin has its own column.

3. Add one of the resistor sides into the common anode with the other side in an unused column.

4. Wire the unused column of the resistor to the 5V line.

5. Repeat steps 2, 3, and 4 for the second seven segment display.

Here is a data sheet on the seven segment displays http://media.digikey.com/pdf/Data%20Sheets/Lite-On...

The seven segment display is a common anode display. Therefore, most of the logic for turning an LED on will be backwards; meaning that setting the pin to high voltage will turn it off and setting it to low will turn the LED on. Also this means that you must have the 5V from the arduino go into the common anode.

Caution: Do not forget to include a current limiting resistor or you will burn out your seven segment display.

STEP3
Solder to printed board

STEP4: HOOK UP TO ARDUINO

1. Plug in the pins to their respective spot .

HC-SR04 Sensor plug insDigital pin 2 which is the input of the TrigDigital pin 4 is the echo input5V to the VCCGND to GNDSeven Segment Display1st seven segment display (ones place) pins 30 through 36Skip pin 7 on the seven segment display as it is the decimal point and not used2nd seven segment display (tens place) pins 37 through 43Skip pin 7 on the seven segment display as it is the decimal point and not used.