Portable Monitor with STONE serial Touch Screen and ESP32

　　

　　Using STONE serial touch screen portable monitor, the hardware department decided to use NXP’s 32-bit microprocessor chip as the whole machine monitoring, ECG analysis, control center, by ECG bioelectricity acquisition amplification, right leg drive, import MIT ECG database to do an algorithm, but also monitor SpO2 sensor electrical signal, blood pressure, respiratory electrical signal amplification, and filtering processing, through high-speed baud rate communication, drive STONE serial touch screen to display waveform and parameter changes in real-time, and compare with a reference value to make a judgment, and monitor and alarm the changes of human body parameters. If there is a range deviation, it automatically issues voice prompts.

　　The new version of the STONE serial touch screen perfectly supports curve depiction and display, the communication protocol is simple and easy to remember, microcontroller engineers can use it after reading the manual, there are many examples of drivers in the command set, directly copied to modify the name and parameters can be used. Serial connection is simple, you can use the official adapter board, whether it is a direct serial connection or USB to serial, it is very convenient and easy to use.  The monitor displays multiple groups of vital parameters at the same time, especially 3 curves that are dynamically drawn and displayed at the same time very smoothly, and should be able to draw more groups of curve graphics at the same time, you can try as needed. Of course, the command set curve function has an example of multiple data pushed at the same time, but the actual use of the current hardware does not respond, I hope the official can be optimized as soon as possible. It may also be solved by updating the firmware. For this new version of the drawing curve function, I first tried how can not be tuned out, and finally learned that the serial screen has a new firmware, brushed the new firmware to see the “real face of the mountain”. Seeing the smooth ECG curve coming out of the serial screen with the firmware brushed, the mood is happy, huh ……

　　The design picture of this project is shown in Figure (1).  The interface is based on a STWI101WT-01 serial screen with 1024*600 resolution, the left side shows 2/3 of the waveform curve and the right 1/3 shows the value.

　　This article will focus on the creation and depiction of the curve chart view. It is completely according to the production process of the project demo, with no classification, maybe you feel messy, but it is the real process of real development.

　　First, we decided to fix the curve depiction of ECG.

　　 
Figure (1) Project Design Expected Interface

　　This demo simulates a 75bpm heart rate, which is equivalent to an 800ms heartbeat, i.e. one point every 40ms, one cycle every 20 points, based on the whole chart view control X axis divided into 100 equal parts, 4s waveform per screen, screen refresh rate 25Hz, looks very smooth. The line series element of this chart view control is set to smooth = false (ECG waveform is sharp), the lower envelope is not displayed, and the point marker is not displayed. area. Here see Figure (4), min = 0, max = 140 for the Y axis, the maximum value given in the program is 130, and the range is relatively full. See Figure (2) – Figure (7) for other parameters, which are set for chart view1 and its elements X axis1, Yaxis2, bar series1, and line series1. We choose transparent rgba (0,0,0,0) for the bg color of the chart view control, which reveals the base color (black), and other controls, such as view, have the same characteristics.
Figure (2) Property settings of chart view1
Figure (3) X axis1 property setting of chart view1
Figure (4) Y axis1 property setting of chart view1
Figure (5) bar series1 property setting of chart view1
Figure (6) The line series1 property setting of chart view111
Figure (7) line series1 property setting of chart view12

　　The programming code to simulate the ECG waveform (75bpm) according to the above settings is as follows.

　　First, define two variables as follows.

　　Then you want to take care of the CO2 curve, focusing on scan synchronization.

　　 

　　The 3 curves of this project, chart view2 is for the SpO2 blood oxygen sensor and chart view3 is for CO2 respiration.

　　Chart view2, chart view3 X axis are set min = 0, max = 100, and ECG chart view1 the same, curve sweep to keep synchronized, chart view2 Y axis2 max = 100, so the preparation of the program Y-axis value is given to 95 maximum, the algorithm is shown in the following program code.

　　Figure (8) shows the ECG waveform at the top and the CO2 waveform at the bottom (symbol round radius = 4)
Figure (9) shows the ECG waveform at the top and the CO2 waveform at the bottom (symbol round radius = 30)

　　The following CO2 waveform in Figure (8) is the effect of the above program when the attribute symbol round radius = 4 for line series3. We try to modify symbol round radius = 30, hoping that the curve transition is more rounded, but the test result is no different from Figure (8), see Figure (9), which shows that when the points are denser, the rounding effect is not obvious. This can only be achieved by changing the point coordinates.
Figure (10) with coordinates separating axes

　　Let’s take a look at the properties of the X axis in Figure (3) by using Figure (10). In Figure (3), when show = true for split line, the long vertical bar (separator bar) will be displayed; when show = true for line, the horizontal line of X-axis will be displayed (such as the horizontal line at the bottom of the top chart view); when show = true for tick, the thin line of the scale below the horizontal line of X-axis will be displayed; when show = true for label, the number below the horizontal line of X-axis (the value filled in data) will be displayed. = true, it will show the number below the horizontal line of the X-axis (the value filled in the data). That’s all.

　　Now it was down to the SpO2 curve and decided to use AD conversion.

　　Curve simulation using ESP32 ADC, it is 12-bit, full scale 4096. chart view2 Y axis max = 255, the ADC read-in value divided by 20, can meet the curve display. The full-scale SPO2 display is 100%, so the ADC read in value divided by 20 and then divided by 2.55 can be displayed in label2, the program because it is an integer number operation, the algorithm is corrected, please see the actual test ok program code. Use the function analogRead(32) in Arduino to read the AD conversion value of GPIO32 (also ADC-CH4) of ESP32 directly. The test can be done by a potentiometer, but also simply connect the ADC-CH4 pin to GND, to +3.3V, to +5V, or overhang to see the interference waveform, see video effect (shown at low when grounded, connected to +3.3V, +5V is the same high full amplitude, the overhang is a spurious curve), the right label2 control timely display ADC voltage changes. The code and algorithm code is as follows.

　　Fig. (11) The actual completed 3 groups of curves partially

　　See Figure (11) for a partial shot of the actual picture, and Figure (12) for the design interface in the computer. As in Figure (3), when the show = false of the split line of the X axis2 of the chart view2, the separator bar of the yellow SPO2 area in the middle of Figure (12) will turn off the display (like the real picture); the smooth waveform of the video display can be done completely as a real-time oscilloscope.
Figure (12) 3 sets of curves completed by computer

　　Reference Points

　　The structure of the STONE designer platform chart view control is shown in Figure (13). There is a detailed description in the official User’s Manual 8.1, including the explanation of each property and parameter; the instruction set 4.24 gives the method of data pushing, see Figure (14), and there are examples of instructions used in the program here.

Figure (13) Structure of the chart view of the curve control
Figure (14) Instructions for using the chart view of the curve control

　　2.  Arduino’s analogRead() read function for analog AD conversion. In the Arduino version 1.8.13 menu “Help”—“Reference” —- “learning —– “Analog I/O”, you can see the description of the analogRead() function As follows.

　　analogRead()

　　Description

　　The Arduino board contains a 6-channel (8 channels on the Mini and Nano, 16 on the Mega), 10-bit analog-to-digital converter. This means that it will map input voltages between 0 and 5 volts into integer values between 0 and 1023. This yields a resolution between readings of 5 volts / 1024 units or, .0049 volts (4.9 mV) per unit. analogReference ().

　　It takes about 100 microseconds (0.0001 s) to read an analog input, so the maximum reading rate is about 10,000 times a second.
Syntax

　　analogRead(pin)
Parameters

　　pin: the number of the analog input pins to read from (0 to 5 on most boards, 0 to 7 on the Mini and Nano, 0 to 15 on the Mega)
Returns

　　int (0 to 1023)
Note

　　If the analog input pin is not connected to anything, the value returned by analogRead() will fluctuate based on a number of factors (e.g. the values of the other analog inputs, how close your hand is to the board, etc.).

　　However, please note that here the ADC-CH4 of ESP32 is 12 bits and the return value will be 0 to 4096. For more details, please refer to the related link in the original article and the ESP32 manual.

　　

　　

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