Difficulty Level = 7 [What’s this?]

Several people in the FPV RC world (that’s First Person View Remote Control for the uninitiated) have contacted me about the possibility of using a Video Experimenter shield as an OSD solution (on screen display). People who fly RC planes and helicopters are increasingly using on-board video cameras to provide a first-person view of the flight, and they like to overlay GPS data onto the video image. Flying radio controlled drones has become a huge hobby (just look how big the DIYDrones and RCGroups communities are!).

I don’t have any RC vehicles, so I’m really on the outside looking in, but I thought I’d experiment to see how useful a Video Experimenter might be in overlaying data onto a video feed. I wrote a simple Arduino program that reads GPS data from the Arduino’s serial RX pin and overlays a heads-up display onto the video input. I think it turned out pretty nice:

Using a Video Experimenter as an OSD

All relevant info is displayed: current latitude/longitude, compass heading, speed (left), altitude (right), and distance home (meters) in the lower right. There’s also a home arrow in the center of the screen pointing toward the hard-coded home location. Note that the ground elevation is also hard coded in the Arduino program so we can calculate altitude.

Circuit Setup

I think there are two ways that a FPV solution could use this approach. If the vehicle is transmitting video and also transmitting GPS telemetry via an XBee radio, then the GPS data can be overlayed onto the video at the ground station. I had to configure the XBee radios to use the same baud rate as my GPS (4800bps).

Circuit for GPS overlay ground station

OR the Arduino and Video Experimenter shield could be onboard the vehicle itself. This way the GPS data is overlayed onto the video before the video is transmitted. In this case, the GPS module is connected directly to the Arduino RX pin, and there’s no XBee radios involved. An Arduino+Video Experimenter shield weigh 2 ounces or 57 grams (I knew you were going to ask that).

I need to be clear that this overlay software can’t run on your ArduPilot hardware. Processing video in an Arduino environment requires nearly all of the ATmega’s SRAM, so there’s no way that this is going to run on the same hardware as your autopilot code.

Again, I’m not in the FPV RC community and don’t have a plane, so I’m not entirely sure how feasible all this is. But a number of RC hobbyists have asked about the Video Experimenter and were enthusiastic about the possibilities. Comments are very welcome!

GPS Configuration

My EM-406 GPS module is configured to only output RMC and GGA sentences, and they are output once per second, so the display only updates at that frequency. It was important to limit the output to only the RMC and GGA sentences, because when using the Arduino video library (TVout), serial communication is accomplished by polling, and it can’t handle data too quickly. To limit the output to RMC and GGA sentences, I wrote these commands to the GPS RX line, with each line followed by a CR and LF character. The Arduino serial terminal works fine for this. Don’t write the comments, of course.

# enable RMC, output 1Hz:
$PSRF103,04,00,01,01*21

# enable GGA, output 1Hz:
$PSRF103,00,00,01,01*25

#disable GLL
$PSRF103,01,00,00,01*25

#disable GSA
$PSRF103,02,00,00,01*26

#disable GSV
$PSRF103,03,00,00,01*27

#desiable VTG
$PSRF103,05,00,00,01*21

If you have a MediaTek GPS module, I believe the correct command to disable all sentences except for RMC and GGA would be this:

$PGCMD,16,1,0,0,0,1*6A

I don’t know how fast of a data feed that the Arduino overlay code can handle, so some experimentation would be in order.

Download

Download the Arduino code OverlayGPS.zip. The awesome TinyGPS library is also required, so install it in your Arduino libraries folder. You also must use the TVout library for Video Experimenter that is required for Video Experimenter projects.

Difficulty Level = 9 [What’s this?]

This was a fun project I built using a perf-board Arduino with GPS receiver, some LEDs, some long wire, some clever code, and a car!

I have this friend that has a speeding problem. So I built this device for my friend so he’ll know when he’s speeding. How will he know? Because when the small perf-board Arduino device with a GPS module detects that his vehicle’s speed is over the speed limit, it turns on a police lights display that is mounted on the inside of his car’s rear windshield. When he sees those flashing police lights in the rear-view mirror, he’ll know he needs to slow down!

Police in the rear view mirror!

OK, it’s me, but you already figured that out. If you weren’t smart, you wouldn’t be here. Here’s a rundown of this project’s features:

• A simple perf-board Arduino circuit with an EM-406a GPS Receiver connected to the microcontroller
• A pair of CAT-5 cables running from the circuit to the back of my Honda Civic
• A small perf-board with red and blue LEDs and two white LEDs representing the headlights of a police car. This small board is mounted on the inside of the rear windshield using suction cups.
• The software running on the microcontroller is programmed to know the speed limit in different locations near where I live and drive. I did this by specifying “speed zones” which are polygons and a speed limit. The polygons are defined as a list of latitude/longitude vertices.
• Whenever the GPS module reports the current position and speed (every second) the code determines which bounding polygon or “speed zone” the car is located in. If the GPS receiver reports that the current speed is greater than the speed zone’s limit, the police lights are activated. If below the speed limit, the lights will be turned off.

The Hardware

Look at this nice clean circuit…

OMG don’t look at the bottom!

Read more…