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QO-100 ground station monitor and control shield using the new Arduino UNO R4 WiFi board. Customisable for generic IOT use also.

I finally found time to address a pending project which had been relegated to the back burner. The original idea was to just substitute the two existing forward and reverse analogue power indicators which I had fitted to my homebrew QO-100 satellite terminal. It quickly became an experimental IOT project opening up many customisable opportunities.

Operating some distance from the ground terminal by ethernet, to curtail coaxial cable losses to the antenna, meant that it was not possible to keep an eye on the SWR meters whilst operating. A more practical remote SWR monitoring solution was needed.

The initial idea was just to remotely read the state of the SWR whilst transmitting from the shack and thus have an immediate warning if something was amiss. This plan quickly avalanched into a bigger project. As well as the state of the SWR, some other equipment parameters could be collected.

The fastest way found to develop a unit to perform this task was to use some already familiar systems. Namely Arduino or ESP32/ESP8266 hardware, C+ coding and then why not incorporate the help of the Internet Of Things.

Using a dashboard means all types of parameters can be neatly displayed and accessed from the shack operating position. Coupled to an IOT service, a dashboard can be accessed from any location and by other users if desired.

Guest dashboards can be created by the administrator and shared so other users can view certain data. Including for example the Maidenhead grid locator when roving, for any grid hunters following the operation.

Reading SWR
A common type of SWR meter used in amateur radio markets contains a dual directional coupler. Directional couplers sample a small amount of power in one direction. A forward and a reverse (or reflected). Later, a diode is used to rectify it before applying to a meter.

The 2.4GHz power amplifier which I used in the transmitter has feedthrough capacitors to test points reading the forward and reverse voltages. This equates to reading the forward and reflected powers at the PA output to the antenna. Although I don’t imagine it to be a precision instrument it is enough to gain an idea of power transfer from the PA to the helix uplink antenna.

In this case, full power from the PA equates to about 3V measured from the directional couplers. Your milage may vary. Plotting the measured values on a graph showed a non linear curve, which tapered slightly towards maximum transmit power. This however is not a problem as we rely more on the relationship between the forward and reverse voltages themselves. Assuming that each side of the directional coupler are reasonably twined with similar components, the two voltage representations will be good enough to derive a basic SWR measurement.

The QO-100 ground station transmits the uplink on 2.4GHz which is an ISM band freely used by many services.
After testing various setups whilst using the narrow band transponder of Oscar 100, no interference was experienced to the Arduino UNO R4 WiFi from the transmitted uplink signal. Your mileage may vary and factors such as uplink power level, device location, distance to router or access point, Tx antenna lobe pattern and signal quality should be considered.
Microcontroller choice.
Does choosing to use the newest Arduino make sense? Well I needed an excuse to try the new UNO R4 board out. Alternatives would have been ESP32, ESP2866 or M5Stack based hardware which I’ve used in previous projects and were also an option. However the uniformity, availability and cost of the Arduino were advantages. In typical Arduino fashion, online information was abundant even for such a new board. It had a built in display and although this LED matrix was a spartan alternative to an LCD or colour OLED screen, its grid of 12x8 LEDs was enough to show what would be needed. It was clear, bright and already included on the board. It would certainly be a big improvement from my dated needle meters currently being used.

The Internet Of Things.
Since IOT is ideal for monitoring and controlling almost anything, the opportunity here lent itself to adding more sensors to gain more information. Other parameters were experimented with and in so doing, added the possibility to access ambient and location data also. Hence, we are not limited to just the ground station equipment parameters, such as antenna SWR and equipment voltages.

Coupling this new UNO R4 microcontroller board with the possibilities afforded by the Arduino IOT Cloud, a feature set was drawn up.

- Numeric display SWR meter.
- Forward and Reverse analogue LED bargraph.
- High SWR warning buzzer.
- High SWR warning red LED.
- Four individual Voltage measurements.
- Current measurement up to 6.4 Amps.
- Temperature, humidity and pressure measurement.
- Global Navigation Satellite System functionality.
- Scrolling Voltages displayed showing Bus, PA, USB1 and USB2 values.
- Scrolling ambient displayed showing Temp, Humidity, Pressure and Maidenhead Locator grid.
- Connection to the Internet Of Things.
- Dashboard monitoring and control.
- OT dashboard accessible with a computer browser.
- IOT dashboard accessible with a smartphone app.
- Graphical representation of data values.
- Dashboard saved data history.
- Dashboard GPS coordinate mapping.
- Lat/Long coordinates and Maidenhead grid displayed.
- Simple homebrew shield installs neatly atop the UNO R4 WIFI.
- Shield solder pads accommodates both through hole or SMD components.
- Two push buttons on shield to test or control (to dashboard also).
- Two green LEDs on shield to test or monitor (from dashboard also).
- Header pins make available many GPIO pins.
- Jumper pins to set program configurations.
- Arduino Reset pin accessible on upper shield PCB.
- PCB shield can be used with other sketches and for other uses.
- Second I2C port availability as first is used for ADC.
- QWIIC/STEMMA connector on I2C port for neat daisy chaining modules.
- Shield allows for future flexible features for changes and experimentation.”

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