SSTV Capsule V2 for High Altitude Balloons

After several attempts we have finally succeeded and in the simplest way possible. This project has been above 30km high sending images in real time using SSTV technology. All of this using free to use PMR walkies. So if we could send images in real time, what are you waiting for? Maybe it doesn't have to be from the stratosphere.... but you could possibly send them from a tree to keep an eye on the all-knowing birds. Or simply test what the International Space Station currently uses to send postcards during its events.

But this has certainly been the best evolution of our project that we presented here in 2017.

As always, here are the components you need to test your project. These are the ones I used, but if you have other radio equipment for example there would be no problem to replace it... in the end we only need to send audio.

On the other hand, regarding the batteries to power the system, we will talk about them later. The link I have left would be the best option but it doesn't have to be the only one. In fact in my last successful flight, I didn't use that system and I didn't find any problem either.

List of components:

-1 x PMR 446 walkie set Not to be confused with model 462 (Link)

-1 x ESP32-CAM + programmer (Link)

-1 x Switch (Link)

Option A power supply:

-1 x 4xAA battery holder (Link)

-4 x Lithium Batteries (optional) (Link)

Option B power supply:

-1 x Lithium Charger TP4056 (Link)

-1 x DC-DC 5V booster (Link)

-1 X Lithium battery 3,7v 1500mah (Link)

I can confess that since I was a child I dreamed of being an astronaut one day, I remember with excitement the first publications in magazines about the ‘successful’ project of the first robot on Mars. I was fascinated by the fact that from the ground they could control the robot from more than 54.6 million kilometres away. At the same time, the International Space Station project began in 1998, which to this day houses astronauts carrying out research projects orbiting at an altitude of 400 km. It turns out that from the ISS and recurrently, the astronauts send small commemorative postcards in SSTV format, I will not go into detail but if you are interested in knowing more about the operation of this system I leave you a link where it is perfectly explained.

In this project we are going to take advantage of the radio system and the SSTV technology to send images in real time from the stratosphere or wherever we have the transmitter.

For this project we propose the use of PMR walkies, surely you have seen them at some time as it is very common to find them in shopping centres or sports shops. These radios have the particularity of not needing a licence to use them, for this reason it is not allowed to modify their antenna or increase their power from 0.5w. However, although the boxes promise a range of 3-5km, we will be able to send signals up to 30km. This is because the signal travels directly from the transmitter to the receiver as it is at a high altitude and does not have to pass through buildings or mountains, in other words there is a direct line of sight between transmitter and receiver.

When you dismantle the radio equipment you will find a board very similar to the one in the image. All we need is the circuit on the top of the walkie next to the antenna. Don't lose sight of the rubber button panel as we need to set up the radio correctly.

The first step before wiring the circuit is to program the esp32-cam, this way we ensure that the code is uploaded without errors and works correctly. To program the esp32 we must do it from the Arduino IDE. As in all cases, as it is a non-generic Arduino board, it will be necessary to download the necessary files. In the following link, you can find all the necessary information to configure it correctly.

Once the esp32-cam has been configured and its correct operation has been checked, it is time to update the code so that it is able to send the images, encode them following the ‘Martin 1’ mode of SSTV and broadcast them through the IO14 pin of the module.

Card manager: https://dl.espressif.com/dl/package_esp32_index.json

You can find the necessary code in the following link, just unzip the folder and run the code with the Arduino.

By default the program sends the images every 10 minutes, this value can be found in line 17 of the code. Before connecting the rest of the components, you can check that it works correctly by connecting the speaker that you previously removed from the walkie to the IO14 and GND pins. At this point, when you power the circuit with the USB cable, it should take the picture and soon after start emitting sound through the speaker. If this happens, Bravo, you have just converted a picture into sound, now you just need to connect it to the radio.

It is very important to check the version of the board manager you have in your Arduino IDE, the code provided is only compatible with the version shown in the image 2.0.17. If you use an updated version of the firmware, it will return an error.

Now that the sstv is working, it is time to connect the microcontroller to the radio. In order to do this, some modifications must first be made to the configuration of the radio equipment.

Transmitter configuration:

1-Chanel 8 / 0

2-VOX 1

3-TO OFF

4-RO OFF

Explanation:

1-Choose the transmission channel/Subtone: By default you can choose channel 8 and disable the subchannel.

2-Activating the VOX: Normally the walkie starts transmitting when the PTT button is pressed, by activating the vox function we allow the walkie to start transmitting automatically when it detects a sound.

3-Deactivating the TO, we prevent the walkie from beeping when pressing the keys.

4-Disable the end tone: By default the walkie emits a characteristic sound at the end of the communication. It is not compulsory, but I prefer to deactivate it.

If you have doubts about the frequency assigned to each channel, you can consult the following table.

Now that the microcontroller and the radio are configured, it is time to make the connection. To do this you will need to use some wires to make the necessary connections.

1-Solder the microphone: The first thing to do is to unsolder/remove the microphone that is built into the walkie by default. To do this I recommend that you heat both points at the same time and remove the microphone with a pair of pliers.

Once the microphone has been removed, you can make the rest of the connections. I will now show the two options that appeared at the beginning:

Once the correct functioning of all the components has been checked, the correct thing to do is to design a pcb that incorporates all the components. To do this, we take advantage of the two holes that the walkie board incorporates, in this way we create a fixed and resistant structure. The pcb will incorporate all the necessary components that will be connected to the walkie through the 4 necessary wires.

Below you can see the images we received in real time from the stratosphere more than 30km away. As you can see, the audio from the walkie is picked up directly from the mobile phone without any cables. This caused some interference due to the ambient noise, but it serves as a sample to check the performance of the system.

To decode the images easily and quickly, I recommend the Robot36 application from the android Playstore.