low cost radar speed sign - led display signs

Do you have a speeding problem?
Interested in defining a solution?
You used to want to build your own low
Radar speed sign?
I live in a street where a car is driving too fast and I am worried about the safety of my children.
I think it would be safer if I could install a radar speed flag that shows the speed so I can slow the driver down.
I searched the internet for the price of buying the radar speed logo, but I found that most of the logos cost more than $1,000, which is quite expensive.
I also don't want to go through the long process of installing the logo in this city because I heard it could cost more than $5,00010,000.
Instead, I decided to build a low
Cost solution yourself and save some money while having some fun.
I found the omnipiresense, which provides a lowcost short-
The distance radar sensor module is perfect for my application.
The shape of the PCB module is very small, only 2. 1 x 2. 3 x 0.
5 inch, only 11 grams in weight.
Electronic products are from
Inclusive and complete-
As a result, there is no power cord, bulky electronics, and a lot of power supply is not required.
The range of large objects like cars is between 50 and 100ft (15m to 30m).
The module accepts all speed measurements, processes all signal processing, and then simply outputs the raw speed data through the USB port. I use a low-
Cost Raspberry Pi (
Or Arduino, or something else with a USB port)
Receive data.
With a little bit of python coding and some big low
Cost led installed on the board, I can display the speed.
My display board can be attached to a pole on the side of the road.
By adding a sign at the top of the display that says "radar check speed", I now have my own radar speed sign to get the driver's attention and slow them down!
All of this is under $500!
I started with the main control hardware, the Raspberry Pi.
The assumption here is that you already have a Raspberry Pi with an operating system and have some experience coding Python.
Raspberry Pi control OPS241-
Radar sensors that receive the reported speed information.
Then convert it to display on large LED 7-Segment Display. a.
I would like to place all electrical components other than radar sensors and LED displays on a single enclosed electronic PCB board installed on the back of the display board.
This makes the board invisible and also far away from the elements.
In this way, only two cables are needed from the back of the board to the front.
One cable is a USB cable that powers the OPS241
A module that receives the measured speed data.
The second cable is drive 7-Segment Display. b.
The PCB board needs to allow enough space for the Raspberry Pi that occupies most of the area.
I also need to make sure that I can easily access several of its ports once installed.
The port I need to access is the USB port (OPS241-
Module A speed data)
Ethernet port (
Develop/debug PC interface for Python code, HDMI port (
Display Raspberry Pi window and debug/develop)
And micro USB ports (
5 v power supply for Raspberry Pi). c.
To provide access to these ports, holes that match the port position on the Raspberry Pi are cut in the enclosure. d.
Next, I need to find space for the breadboard with independent electronic components to drive the display LEDs.
This is the second largest commodity.
There needs to be enough space around it, and I can jump from Raspberry Pi to it and output the signal to the head that drives the LEDs.
Ideally, if I had more time, I would have soldered the components and wires directly to the PCB board instead of using the breadboard, but that was good enough for my purposes. e.
I plan to have a display drive head next to the breadboard on the edge of the PCB so that I can keep my wire short in length and also so that I can cut a hole in the lid, and plug the cable into the connector. f.
Finally, I set aside space on the PCB for the power block.
The level converter and display drive need 5 V and the led needs 12 V.
I connect the standard 5 v/12 v power connector to the power block and then route the power signal from that block to the breadboard and the LED head.
I made a hole in the lid so I could connect the 12 V/5 v power cord to the power connector. g.
This is what the final electronic PCB plan looks like (with cover off)
: I use 4 spacers, screws and nuts to install my Raspberry Pi on a perforated and plated PCB board.
I like to use the plated PCB board so that I can weld the components and wires if needed.
A maximum of 3 can be obtained by Raspberry Pi GPOs. 3V each.
But the LED display needs a 5 v control signal.
So I need to design a simple, low
Cost of circuit to level-
Take the Pi control signal from 3. 3V to 5V.
The circuit I am using consists of 3 Discrete FET transistors, 3 discrete resistors and 3 integrated inverters.
The input signal comes from the Raspberry Pi GPOs and the output signal is routed to the title connected to the cable from the led.
This signal is converted to the ldd clk of the gpo23 SparkFun, the LDD latitude of the gpo4sparkfun, and the ldd ser of the SPIO5 SparkFun.
To show the speed, I used two large LEDs I found on SparkFun. They are 6.
It should be readable from a distance.
To make them more readable, I covered the white background with blue tape, although the black might provide more contrast.
Each LED requires a serial shift register and latch to hold the control signal from the Raspberry Pi and drive the LED segment.
SparkFun is very well written.
Do it here.
Raspberry Pi sends serial data to LED 7-
Segment Display and control latch timing.
The drive board is mounted on the back of the LED and cannot be seen from the front. The OPS241-
The radar sensor was scanned into a 3D print stand made for me by a friend.
Or, I can screw it straight to the board.
The radar sensor is mounted on the front of the board, near the LEDs.
The sensor module is equipped with an antenna (
Gold patch on top of board)
While the spec sheet says the antenna pattern is very symmetrical in both horizontal and vertical directions, it might be nice to rotate it 90 °.
When mounted to the pole, the radar sensor goes outward along the street.
Tried several different heights and found it to be around 6 (2 m)
Be the best.
A little higher, I suggest that it might tilt down a bit.
There are two power supplies for this logo.
One is the power supply of the converted hard disk that provides 12 v and 5 v. The 7-
For led and 5 v signal levels, 12 V is required for segment display.
The converter board takes 3.
As mentioned above, 3 v signals and levels from Raspberry Pi transfer them to 5 v for display.
Another power supply is a standard mobile phone or tablet 5 v USB adapter with USB micro connector for Raspberry Pi.
To keep the radar sensors, LEDs and controller boards, everything is mounted on a piece of wood that is 12x24x1.
The Led is mounted on the front side with the radar sensor, and the controller board is mounted in the housing on the back.
The wood is painted black to help make the LEDs more readable.
The power and control signals of the LED are routed through a hole in the wood behind the LED.
The radar sensor is mounted on the front side next to the LEDs.
The USB power and control cable of the radar sensor is wrapped on the top of the board.
Tie a few holes in the top of the board
Wraps provides a way to install the circuit board on the pole next to the "radar check speed" sign.
The controller board is bolted together with the power adapter to the back of the board.
Python running on Raspberry Pi is used to pull the system together.
The code is located on GitHub.
The main part of the code is configuration settings, reading data via USB
The serial port of the radar sensor, which converts the speed data to display and displays timing control.
Default configuration on OPS241-
The radar sensor is fine, but I found that some adjustments are needed to start the configuration.
These include changing from the m/s report to the mph, changing the sampling rate to 20 ksps, and adjusting the static noise settings.
The sampling rate directly determines the maximum speed that can be reported (139mph)
The report was accelerated.
The key learning is the squelch value setting.
At first I found that the radar sensor did not pick up the car in a long range, maybe only 15-30 feet (5-10m).
I think I might have set the radar sensor too high because it's about 7 feet above the street.
Lowering it to 4 feet doesn't seem to help.
Then I see the squelch setting in the API documentation and change it to the most sensitive (QI or 10).
With this, the detection range increased significantly to 30-100 feet (10-30m).
It is quite direct to receive the data through the serial port and convert it to send to the LEDs.
At 20 ksps, the speed data is reported at 4-
6 times per second
It's a bit fast and it's not good to make the monitor change so fast.
The display control code was added to look up the fastest report speed per second, and then the number was displayed.
This makes the report number delayed for one second, but it doesn't matter, or it's easy to adjust.
I myself tested driving a car through it at a set speed and the reading matched my speed relatively.
OmniPreSense said they have tested the module and it can pass the same test as the standard police radar gun with an accuracy of 0. 5 mph.
All in all, this is a great project and a great way to build for the safety of my street.
There are some improvements that can make it more useful, which I will discuss in the article belowon update.
The first is to find a larger and brighter LEDs.
The data sheet shows that these are 200-300 mcd (millicandela).
Definitely need something higher than this, as the sun can easily disappear in daylight.
Alternatively, adding a shield around the edge of the led prevents sunlight from shining.
If it is to be released permanently, it is necessary to produce weather proof of the whole solution.
Fortunately, this is the radar, the signal is easy to pass through the plastic housing, only need to find a suitable size, also waterproof.
Finally, adding a camera module to the Raspberry Pi to take pictures of anyone who exceeds our street speed limit would be awesome.
I can use on-
Get on WiFi and send alerts and pictures of speeding cars.
Adding a timestamp, date, and detected speed to the image will really complete the task.
Maybe there's even a simple app that shows the information well.