This is how the transceiver nodes on the breadboard look like after adding a 7333 voltage regulator. A portable version with a touchscreen and fed from a 9V battery has been created.
You can read Part 1 here: https://arduinoenigma.blogspot.com/2025/12/experimenting-with-lora-using-reyax.html
In the previous post, it was determined that without a voltage regulator, the RYL998 would brown out the Arduino Nano. After a lot of research, we settled on a LDO (Low Dropout Regulator). The 7333 is an inexpensive part that can be fed 5V and it will produce 3.3V on its output.
The 7333 has two different pinouts. The following diagram shows the 7333A 3.3V voltage regulator:
And here is the circuit using the 7333B, the difference in the pinout is the location of the VIN and GND pins are swapped.
This circuit was prototyped on the breadboards, the modules reset to factory defaults using the AT+FACTORY command, reprogrammed with AT+ADDRESS=1 to have addresses of 1 and 2. One node was program to send data and the other one receives it. The nodes are stable at full transmit power even though one Arduino uses its 5V output to power the other node, so it it powering another Arduino and two voltage regulators. This proves the voltage regulators have enough built in margin.
The picture below shows the 7333 in the breadboard.
Once the circuit was proven on the breadboards, it was moved to a GIKFUN Prototype Shield ($15 for 3). It has the voltage regulator and the voltage divider to convert Arduino Software Serial TX from 5V to the 3.3V the 998 expects. The ICSP header with the long legs is needed for the SEEED Touchscreen and must be ordered separately, try searching for "6 PIN Double Row Straight Female PIN Header 2.54MM Pitch pin Long"
Here is the assembled node using an Arduino Uno, a custom shield and a touchscreen.
This shows the location of the antenna. The goal was to protect it against damage, but it may have been placed in a sub optimal location. The antenna is located between a metal part and the Arduino, a better location might be on the other side, using connectors, it can be extended out so it is exposed.
A sketch running on the handheld device was written to display a received message on the screen. A node in the breadboard sends AT+SEND=0,5,DATA! to the 998. The 998 on the shield receives the data and puts out on the serial port +RCV=1,5,DATA!,-17,11. The sketch on the handheld uses the first three characters to identify the receive command. Once the +RC command is received, the rest is displayed. The last two parameters, -17 and 11 show the Received Signal Strength Indicator (RSSI) and Signal-to-Noise ratio (S/N). The RSSI starts at 0 when the nodes are very close to each other and goes down. The S/N starts at 11 and goes down to -15. After a new message is received, the rectangle below the message toggles between red and green.
The breadboard was left inside a building and the handheld was taken out for a walk. The rectangle kept toggling between red and green while the RSSI and the S/N decreased. At 684 ft and with a signal strength of -111 and a signal to noise ratio of -15, it stopped toggling. The 684 foot range was through multiple buildings and trees.
How to convert the RSSI and the S/N to a cell phone style signal strenght indicator with 5 or 6 antenna bars? One idea is to disregard the S/N and convert the RSSI range of 0 to -111 to a range or 0 to 6 antenna bars. The other idea is to add the RSSI and the S/N together, it ranges from (0,11) to (-111,-15) and then convert to antenna bars.
Another experiment can be run by moving the module out so the antenna is exposed.
Next is to design a PCB and send it to Oshpark for manufacturing.
Source code is at https://github.com/arduinoenigma/REYAX-RYLR998-Tests
(To be continued...)
No comments:
Post a Comment