This MATLAB visualization calculates the dewpoint from temperature and humidity. The formula is given at https://en.wikipedia.org/wiki/Dew_point. The values are taken from your ThingSpeak channel at the time your webpage is opened. You must manually update the chart by refreshing your browser.
% Read Humidity and Temperature from a ThingSpeak channel to calculate dew point. % (C) 2020 Karl Berger % 21 November 2018 - changed to Matlab plot % 30 October 2019 - changed to Numminutes in thingSpeakRead % Script expects temperature in °C. It then calculates dewpoint in °C. % Calculated temperatures are converted to °F for charting. % If you read temperature in °F, you must first convert it to °C % before doing the dewpoint calculation. %%% ENTER YOUR CHANNEL ID chID = 286120; %% IoT Kits field definitions TempCFld = 1; % Temperature Field ID HumidFld = 2; % Humidity Field ID % Number of data points to plot dataMinutes = 2 * 24 * 60; % days * 24 hours * 60 minutes/hour % Read field data and time for Temperature sensor [tempC, time] = thingSpeakRead(chID, 'Fields', TempCFld, 'NumMinutes', dataMinutes); % Read field data for Humidity sensor humidity = thingSpeakRead(chID, 'Fields', HumidFld, 'NumMinutes', dataMinutes); % Calculate dew point % Specify the constants for water vapor (b) and barometric (c) pressure. % NOAA constants https://en.wikipedia.org/wiki/Dew_point b = 17.67; c = 243.5; % Calculate the intermediate value 'gamma' gamma = log(humidity / 100) + b * tempC ./ (c + tempC); % Calculate dew point in Celsius dewPointC = c * gamma ./ (b - gamma); % Convert temperatures to Fahrenheit for display dewPointF = (dewPointC * 1.8) + 32; tempF = (tempC * 1.8) + 32; plot(time, [dewPointF, tempF], 'Linewidth', 2) ylabel('Temperature (°F)') xlabel('2-day span') legend('Dew Point °F', 'Temp °F', 'Location', 'Best') grid on