Tag Archives: BrownOut

.NET nanoFramework RAK11200 – Brownout Voltage Revisited

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The voltage my test setup was calculating looked wrong, then I realised that the sample calculation in the RAK Wireless forums wasn’t applicable to my setup.

I reassembled my RAK11200 WisBlock WiFi Module, RAK19001 WisBlock Base Board, RAK1901 WisBlock Temperature and Humidity Sensor, 1200mAH Lithium Polymer (LiPo) battery, SKU920100 Solar Board test setup, put a new 9V battery (I had forgotten to turn it off last-time) in my multimeter then collected some data. A=ReadValue(), C= ReadRatio(), E= measured battery voltage.

Excel spreadsheet for calculating ratio

I updated the formula used to calculate the battery voltage and deployed the application

public static void Main()
{
    Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} devMobile.IoT.RAK.Wisblock.AzureIoTHub.RAK11200.PowerSleep starting");

    Thread.Sleep(5000);

    try
    {
        double batteryVoltage;

        Configuration.SetPinFunction(Gpio.IO04, DeviceFunction.I2C1_DATA);
        Configuration.SetPinFunction(Gpio.IO05, DeviceFunction.I2C1_CLOCK);

        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Battery voltage measurement");

        // Configure Analog input (AIN0) port then read the "battery charge"
        AdcController adcController = new AdcController();

        using (AdcChannel batteryVoltageAdcChannel = adcController.OpenChannel(AdcControllerChannel))
        {
            batteryVoltage = batteryVoltageAdcChannel.ReadValue() / 723.7685;

            Debug.WriteLine($" BatteryVoltage {batteryVoltage:F2}");

            if (batteryVoltage < Config.BatteryVoltageBrownOutThreshold)
            {
                Sleep.EnableWakeupByTimer(Config.FailureRetryInterval);
                Sleep.StartDeepSleep();
            }
        }
        catch (Exception ex)
        {
...    
}

To test the accuracy of the voltage calculation I am going to run my setup on the office windowsill for a week regularly measuring the voltage. Then, turn the solar panel over (so the battery is not getting charged) and monitor the battery discharging until the RAK11200 WisBlock WiFi Module won’t connect to the network.

.NET nanoFramework RAK11200 – Brownout Voltage

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My test setup was a RAK11200 WisBlock WiFi Module, RAK19001 WisBlock Base Board, RAK1901 WisBlock Temperature and Humidity Sensor, 1200mAH Lithium Polymer (LiPo) battery and SKU920100 Solar Board. The test setup uploads temperature, humidity and battery voltage telemetry to an Azure IoT Hub every 5 minutes (short delay so battery life reduced).

The first step was to check that I could get a “battery voltage” value for the RAKWireless RAK11200 WisBlock WiFi Module on a RAK19001 WisBlock Base Board for managing “brownouts” and send to my Azure IoT Hub.

RAK19001 Power supply schematic

The RAK19001 WisBlock Base Board has a voltage divider (R4&R5 with output ADC_VBAT) which is connected to pin 21(AIN0) on the CPU slot connector.

RAK19001 connector schematic

The RAK19001 WisBlock Base Board has quite a low leakage current so the majority of the power consumption should be the RAK11200 WisBlock WiFi Module.

RAK19001 leakage current from specifications

I used AdcController + AdcChannel to read AIN0 and modified the code using the formula (for a RAK4631 module) in the RAK Wireless forums to calculate the battery voltage. (UPDATE This calculation is not applicable to my scenario)

RAK11200 Schematic with battery voltage analog input highlighted

When “slept” the RAK11200 WisBlock WiFi Module power consumption is very low

RAK11200 low power current from specifications
public static void Main()
{
    Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} devMobile.IoT.RAK.Wisblock.AzureIoTHub.RAK11200.PowerSleep starting");

    Thread.Sleep(5000); // This do debugger can attach consider removing in realease version

    try
    {
        double batteryVoltage;

        Configuration.SetPinFunction(Gpio.IO04, DeviceFunction.I2C1_DATA);
        Configuration.SetPinFunction(Gpio.IO05, DeviceFunction.I2C1_CLOCK);

        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Battery voltage measurement");

        // Configure Analog input (AIN0) port then read the "battery charge"
        AdcController adcController = new AdcController();

        using (AdcChannel batteryVoltageAdcChannel = adcController.OpenChannel(AdcControllerChannel))
        {

            // https://forum.rakwireless.com/t/custom-li-ion-battery-voltage-calculation-in-rak4630/4401/7
            // When I checked with multimeter I had to increase 1.72 to 1.9
            batteryVoltage = batteryVoltageAdcChannel.ReadValue() * (3.0 / 4096) * 1.9;

            Debug.WriteLine($" BatteryVoltage {batteryVoltage:F2}");

            if (batteryVoltage < Config.BatteryVoltageBrownOutThreshold)
            {
                Sleep.EnableWakeupByTimer(Config.FailureRetryInterval);
                Sleep.StartDeepSleep();
            }
        }

        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Wifi connecting");

        if (!WifiNetworkHelper.ConnectDhcp(Config.Ssid, Config.Password, requiresDateTime: true))
        {
            if (NetworkHelper.HelperException != null)
            {
                Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} WifiNetworkHelper.ConnectDhcp failed {NetworkHelper.HelperException}");
            }

            Sleep.EnableWakeupByTimer(Config.FailureRetryInterval);
            Sleep.StartDeepSleep();
        }
        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Wifi connected");

        // Configure the SHTC3 
        I2cConnectionSettings settings = new(I2cDeviceBusID, Shtc3.DefaultI2cAddress);

        string payload ;

        using (I2cDevice device = I2cDevice.Create(settings))
        using (Shtc3 shtc3 = new(device))
        {
            if (shtc3.TryGetTemperatureAndHumidity(out var temperature, out var relativeHumidity))
            {
                Debug.WriteLine($" Temperature {temperature.DegreesCelsius:F1}°C Humidity {relativeHumidity.Value:F0}% BatteryVoltage {batteryVoltage:F2}");

                payload = $"{{\"RelativeHumidity\":{relativeHumidity.Value:F0},\"Temperature\":{temperature.DegreesCelsius:F1}, \"BatteryVoltage\":{batteryVoltage:F2}}}";
            }
            else
            {
                Debug.WriteLine($" BatteryVoltage {batteryVoltage:F2}");

                payload = $"{{\"BatteryVoltage\":{batteryVoltage:F2}}}";
            }

#if SLEEP_SHT3C
            shtc3.Sleep();
#endif
        }

        // Configure the HttpClient uri, certificate, and authorization
        string uri = $"{Config.AzureIoTHubHostName}.azure-devices.net/devices/{Config.DeviceID}";

        HttpClient httpClient = new HttpClient()
        {
            SslProtocols = System.Net.Security.SslProtocols.Tls12,
            HttpsAuthentCert = new X509Certificate(Config.DigiCertBaltimoreCyberTrustRoot),
            BaseAddress = new Uri($"https://{uri}/messages/events?api-version=2020-03-13"),
        };
        httpClient.DefaultRequestHeaders.Add("Authorization", SasTokenGenerate(uri, Config.Key, DateTime.UtcNow.Add(Config.SasTokenRenewFor)));

        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Azure IoT Hub device {Config.DeviceID} telemetry update start");

        HttpResponseMessage response = httpClient.Post("", new StringContent(payload));

        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Response code:{response.StatusCode}");

        response.EnsureSuccessStatusCode();
    }
    catch (Exception ex)
    {
        Debug.WriteLine($"{DateTime.UtcNow:HH:mm:ss} Azure IoT Hub telemetry update failed:{ex.Message} {ex?.InnerException?.Message}");

        Sleep.EnableWakeupByTimer(Config.FailureRetryInterval);
        Sleep.StartDeepSleep();
    }

    Sleep.EnableWakeupByTimer(Config.TelemetryUploadInterval);
#if SLEEP_LIGHT
    Sleep.StartLightSleep();
#endif
#if SLEEP_DEEP
    Sleep.StartDeepSleep();
#endif
}

The nanoFramework.Hardware.Esp32.Sleep functionality supports LightSleep and DeepSleep states. The ESP32 device can be “woken up” by GPIO pin(s), Touch pad activity or by a Timer.

RAK11200+RAK19007+RAK1901+ LiPo battery test rig

After some “tinkering” I found the voltage calculation was surprisingly accurate (usually within 0.01V) for my RAK19001 and RAK19007 base boards.

When the battery voltage was close to its minimum working voltage of the ESP32 device it would reboot when the WifiNetworkHelper.ConnectDhcp method was called. This would quickly drain the battery flat even when the solar panel was trying to charge the battery.

Now, before trying to connect to the wireless network the battery voltage is checked and if too low (more experimentation required) the device goes into a deep sleep for a configurable period (more experimentation required). This is so the solar panel can charge the battery to a level where wireless connectivity will work.