Affordable Speeding and Vehicle License Plate Recognition System

With the pandemic and fewer cars on the road, it seems like there is even more speeding occurring at even faster speeds. Somebody is going to get hurt.

It would be nice to have a simple way to capture information about the speeders including their license plate to share with the police. But license plate recognition systems cost between $5,000-10,000, way too much for my budget. However, here’s a much more affordable approach. For around $350, you can make your own detection system using an old smartphone phone, a free app, and a radar sensor from OmniPreSense. The total solution is easily mounted to capture the speeding vehicle including a picture with all the relevant information. The license plate is easily readable from the image captured. It is still a bit manual to read out the licenses but at least it will not cost $1,000s to get this information.

1. Android Radar Gun App (free)
2. Android phone or tablet with USB-OTG splitter support
   1. Manufacturer: LG G4 (used)
   2. Price: $60
   3. Supplier: Ebay
3. USB-OTG splitter cable
   1. Manufacturer: TVxStream, model 8541671592
   2. Price: $6.24
   3. Supplier: Amazon
4. USB micro cable, 10” , right angled connector (x2)
   1. Manufacturer: various
   2. Price: $7.50
   3. Supplier: Amazon
5. OPS243-A Radar Sensor
   1. Manufacturer: OmniPreSense, model OPS243-A
   2. Price: $209
   3. Supplier: Mouser
6. 30,000mAHr battery
   1. Manufacturer: various
   2. Model: 30,000mAHr battery pack
   3. Price: $32.99
   4. Supplier: Amazon
7. All-weather enclosure
   1. Manufacturer: Bud Industries, model: PTS-25338
   2. Price: $29
   3. Supplier: Digikey
8. 3D printed sensor mount (custom design)
9. Double Sided Velcro tape

Download the radar gun app onto your smartphone or tablet. The app is free. It asks for usage of your camera and location. The location is added to the information overlaid on the images by the app. The app will place the date, time, speed, and location if available as part of the image that is captured. The older LG G4 phone used didn’t have a SIM card so no location information was available. But, I was able to hotspot it to my phone to get location information.

1. Do a trial placement of the phone/camera, battery, and radar sensor in the enclosure to figure out how they will fit together.
2. The radar sensor needs to “see” the road, so it needs to be facing the front of the enclosure (top lid).
3. The LG phone is a bit large and the camera likewise needs to look out into the road. Because of this the phone needs to be in the top lid. The phone should be orientated like you would normally hold it for a picture so the overlaid time, date, speed, and location information in placed correctly.
4. The USB connector/cable requires space as well. It was a little tight so we ended up using right angled USB micro connector cables for more clearance inside the enclosure.
5. The battery is also a little large but it can go in the back/bottom of the enclosure.

1. To position the radar sensor correctly I had a friend design a 3D printed mount. It'll hold the radar sensor in place when mounted.
2. The system is going to be mounted around 7-10 ft. high so it is above any parked cars and also keep it out of site or reach of a passerby. As such, the mount has the sensor angled looking down 10 degrees, so it looks into the road better to pick the cars up.
3. Make sure to install it so the sensor will be looking down into the street and not up into the sky. You'll miss detection of cars if that were the case.
4. The design file for the radar sensor mount is provided here.

1. The phones camera needs to see the road which requires cutting a hole in the enclosure. The LG G4 camera lens size was measured at 10 mm so a 3/8 in. drill bit was used.
2. Position the camera in the backside of the enclosure lid and mark its position. Take an appropriate size drill and drill a hole in the top lid where the marking was made. Once the hole is done you can turn the camera on the phone and aim it through the hole to see if it has a clear picture. My original size and drill point was a little off so I used a file to take away a bit more of the enclosure plastic.
3. Use Velcro to mount the camera into position so it can see out the hole in the enclosure lid. This won't be water proof but maybe that'll be a future update to the design.

1. The cables should be connected as shown in the picture here. The key is the USB-OTG micro or C connector goes into your phone and provides a Type A female and a USB micro female connector for the sensor and battery.
   1. USB-OTG splitter micro male to phone
   2. USB-OTG splitter Type A female connector to regular USB-micro cable to radar sensor
   3. USB-OTG splitter female micro connect to regular USB-micro cable to battery
2. If there's a space constraint, you can use USB cables with right angle connectors.
3. I’ve read someplace you should plug the USB-OTG cable into the phone first so we'll do that just to be safe.
4. You may want to have everything connected (phone, sensor, battery) as you do the next steps or reconnect them as you install them.

1. Use Velcro on the underside and bottom of the battery to keep it secure in the enclosure.
2. The sensor snaps into the 3D printed mount and connect the USB micro cable if not done. We had to use the right angled USB micro connector for the sensor connection for proper clearance.
3. The battery will charge the phone and sensor at the same time. I used a 30,000mAHr battery. Offline I had measured the total current consumed by the phone and radar sensor at 400mA. The battery will thus provide around 75 hours or 3 days of operation.

1. Using Velcro again to lock the phone in place making sure the camera can see out the hole. You can turn the camera on to see that its mounted correctly with a good view through the hole.
2. Connect USB cable and provide phone power.

1. Start the phone
2. Open the app and swipe to the 2nd screen
3. Set the speed limit for the street and threshold for when to take a picture. In my case I used 25mph street speed and 35mph trip speed.

1. Carefully close the lid and tighten down the screws.
2. Everything is powered on so move to your location near the street for mounting.
3. I had a piece of metal plate which I mounted to the back of the sensor to allow tie-wraps for connecting to the pole.
4. The pole location is around 3 ft. from the street and I'm mounting it facing roughly North so it won't be looking into the sun at all.
5. The sensor is mounted around 7 ft. high and angling the sensor to look into the road. I angled 10-20 degrees looking into the road from from parallel to the road so it can catch the cars correctly. The radar will report the speed very accurately (+/-1mph) but they will have an error in the reported value based on the cosine angle between where the sensor is looking and the cars location. Angling the system into the road 10-20 degrees keeps this error to a minimum (1-2%).
6. The enclosure is an all-weather enclosure although we have a hole in it for the camera. We will limit its usage to non-rainy days. We will have to work on protecting the camera from the rain in a further update.

1. I left it up for a few hours initially to see how it performed.
2. When the battery should be done or your desired time, take down the system, open it up, and see who you've caught.
3. There they are, our local speeders. A reported negative speed is a car going away from the sensor while a positive speed is towards it. That helps for the case of two cars in the picture to know who's doing the speeding.
4. I’ve blurred out the license plate here, but they were very readable along with the noted date, time, and speed. Now, where's that police info email address....