How to Make an Explorer Probe for Rockets With DHT11 and an ESP8266

With probes reaching the deepest parts of our solar system and making important discoveries—and drones giving perspective in places that we could never go—it is clear that electronics play a central role. So, why not get yourself involved with discovery and adventure? In this DIY hacking series, we will build a small explorer probe that is designed to sit in a small rocket (such as a water rocket), land, and relay data back to a server using RIOTOUS.

Schematic

How Does the Explorer Probe Work?

The magic behind the explorer in this project is achieved at two fronts: hardware and software. The hardware for this project has been designed to be as simple as possible, as to reduce the chance of damage during flight and landing (we all remember how the Beagle 2 Mars lander went). The circuit itself only consists of the needed modules connected to the main controller (PIC18F25K20), a DHT111 temperature/humidity sensor, an ESP8266 Wi-Fi module, and some power circuitry based on the AMS1117 3.3V regulator.

The DHT111 module is mounted externally, as to save space on the PCB (the PCB needs to be as small as possible). The module must be stored in the shade and kept away from water, so it is advised that the probe has air vents to allow the probe to measure the air temperature and humidity. But also to try and prevent water from entering the probe. The ESP8266 module is mounted externally, as to improve the reception for the receiver. The ESP8266 module, despite using Wi-Fi, has an incredible range (with the right transceiver) of up to 1130 meters. Therefore, the module should be mounted on the top of the probe to improve the chance of detection by the receiver. The power circuitry not only contains the needed decoupling capacitors, but also some protection diodes. D1 prevents damage to the circuit if the input polarity is wrong, and D2 prevents large voltage spikes on the VCC power-line from damaging the regulator.

The software for the probe is based on the RIOTOUS framework, which stands for real-time internet of things of unusual size. It is designed to allow internet access for small microcontrollers while still keeping RAM overheads low. The code is rather simple, and it contains all the instructions needed to make the DHT111 work, make readings, and then transmit those readings to a server of your own choice. However, this tutorial does not handle the server side (our receiver), and that will be covered in part two, where we will build a command center, including a dish to find our probe. To learn more about RIOTOUS, see the AAC projects below:

Construction

Powering the probe is entirely up to you, but this project uses coin cells because they are lightweight and very portable. However, coin cells do not last long and are more suited for one-off launches where data is only expected to be relayed back for a day or so. A more long-term solution would involve small solar cells that charge a battery and then turn the probe on once enough charge has been stored.