"Have you ever taken your child to the hospital? I believe that besides injection and hanging water, taking body temperature is also a very noisy and unwilling thing for children. In particular, measuring with mercury thermometer is not only inefficient, troublesome, but also dangerous. (of course, mercury thermometer is not good for nothing, at least the measurement is accurate). However, with the rapid development of various electronic temperature measuring equipment, such as electronic ear temperature gun, Infrared electronic thermometer, etc. the reliability of electronic thermometer has been further improved and the measurement is more accurate. Some large general hospitals in China have begun to try to use electronic thermometer to replace the traditional mercury thermometer for preliminary temperature measurement. There is no unique couple. These operations are convenient and fast, The electronic thermometer with intuitive interface display has also become the first choice of most families, as one of the necessary "family guards".
So, such a popular electronic thermometer, can we DIY one ourselves? Of course, the answer is yes. For example, the ADI eval-aducm360qspz development kit obtained by aiban.com itself is a good reference development scheme for electronic temperature measurement. The evaluation board is based on ADI's single-chip data acquisition microcontroller aducm360 (aducm360 data manual).
Well, let's first understand what this evaluation suite looks like?
Accessories in the box include:
Eval aducm360mkz evaluation board
J-link ob simulator
USB cable, data CD (including ide tools, schematic diagram of development board, routine code, start-up guidance documents, etc.)
The packaging box of eval-aducm360qspz development kit belongs to a relatively "simple" type, so I won't say much. However, what surprises people is the accessories in the box, which is really "things can't be judged by appearance".
The first is the evaluation board eval-aducm360mkz, as shown in the following figure (left). Who could have thought that the board size is only 62mm * 21.6mm, which is too small and surprising. According to preliminary observation, the whole board is basically a "minimum system board" based on aducm360 microcontroller.
In addition, it is surprising that the development kit includes a j-link ob emulator in addition to the evaluation board and CD-ROM materials, which can not only save engineers the cost of purchasing the emulator, but also carry out rapid product development. It seems that ADI is very considerate about its own product development experience.
Aducm360 analog microcontroller
As mentioned above, eval-aducm360mkz evaluation board is mainly a simple development platform designed by aducm360 microcontroller. Why don't we start with the main controller to understand the functions of the board, as shown in the figure below
The specific model of the microcontroller carried on the aducm360mkz evaluation board is aducm360bcpz128 (aducm360bcpz128 data manual), which adopts 48 pin lfcsp package with a size of 7mm * 7mm. Its main characteristics are as follows:
Based on 32-bit arm Cortex-M3 processor, 128KB flash / EE and 8KB SRAM are integrated
Integrate an on-chip 32 kHz oscillator and an internal 16 MHz high frequency oscillator
Two 24 bit ADCs (ADC0 and ADC1) are integrated, the conversion rate is 3.5hz ~ 3.906khz, 50 Hz / 60 Hz synchronous noise suppression
Both ADCs adopt flexible input multiplexing, which can realize 6-channel differential or 11 channel single ended input channels
4 internal channels for monitoring DAC, temperature sensor, iovdd / 4 and avdd / 4 (ADC1 only)
Programmable gain (1 to 128)
Root mean square (RMS) noise: 52 NV (at 3.75 Hz), 200 NV (at 50 Hz)
Programmable sensor excitation current source
On chip 1.2V precision reference voltage source
A 12 bit DAC converter, NPN mode, can be used for 4 mA to 20 mA current loop applications
UART, I2C and 2 × SPI serial I / O, 16 bit PWM controller, 19 pin multifunction GPIO port
2 general purpose timers, wake-up timer / watchdog timer, multi-channel DMA and interrupt controller
It has a variety of low-power working modes, and the sleep power consumption is only 4ua
Operating voltage range: 1.8 V to 3.6 V; Rated operating temperature range: − 40 ° C to + 125 ° C
Regardless of parameters, aducm360, as an analog microcontroller with AD conversion function, can be mainly divided into two parts: one part is the data acquisition and conversion simulation part based on two ADC units (not limited to ADC function, such as the same DAC function), and the other part is based on arm Cortex-M3 processor, including flash The control unit part composed of some common peripheral resources such as SRAM is shown in the following figure (next page)
Simulation part
As we all know, data processing and conversion has always been the strength of ADI company. We also see that two 24 bit high-precision microcontrollers are integrated on the aducm360 microcontroller with the main analog-to-digital conversion function Δ-Σ ADC has a sampling rate of 3.9ksps. If you look at the internal structure of the microcontroller (as shown in the figure below), you can find that the two ADCs are connected to a flexible input multiplexer, so that the two ADCs can work in both fully differential configuration mode and single ended mode. The application is quite flexible and unlimited.
Let's look at the internal structure of the two ADCs (as shown in the red circle in the figure above), including two filters in parallel: a sinc3 or sinc4 filter in parallel with sinc2 filter. What are the benefits of adopting this design structure?
Let's start with the functions of these filters. We can adopt different configurations according to different application requirements, such as:
Sinc3 or sinc4 filters are used for precision measurement
Sinc2 filter is used for fast measurement and step change detection of input signal
In addition to the main ADC functions, the analog part also includes a 1.2V reference voltage source, a single channel buffered voltage output DAC, etc. it is not introduced here. For details, please refer to the chip specification on the ADI official website.
control section
At this time, let's look at the control of aducm360 microcontroller. This part is relatively familiar and easy to understand. ADI selects arm Cortex-M3 processor with a wide ecosystem as the main control. Engineers who have been working in the field of microcontroller for many years know more or less that m3 is the earliest M-series processing core launched by arm company, with low power consumption, stability and reliability, and has been used for many years, (Apple's coprocessor is also based on this processor) the performance is between M0 and M4. Compared with the well-known cortex-m4 processor, it can be seen as less support for DSP instruction set and FPU unit. It can be said that the Cortex-M3 processor selected by ADI for arm is the result of comprehensive consideration of applicability, power consumption, performance and other factors.
Aducm360 microcontroller positioning
After we have a preliminary understanding of the characteristics of the whole aducm360 microcontroller, the problem comes. Why is the microcontroller of ADI suitable for the field of temperature measurement at the beginning of the article? What is the specific measurement?
I believe many people have such questions. Before answering this question, let's take a look at some ADC products or development boards evaluated by Aiban before to see if we can get some inspiration from these products（ Mainly discuss ADC function)
The products listed here mainly include Ti ads1118 evaluation board (based on Ti) Ads1118), Omega brand digital thermometer (based on rich crystal fs98o22), weishirui intelligent tester wavexpert （ Based on Ti ads4225), these products have just been evaluated or disassembled by aiban.com in the past
According to the above products without application, we can simply divide them into two categories: one is the application of temperature measurement, and the other is the oscilloscope application represented by weishirui. We can compare the most basic parameters, resolution and sampling rate of their ADC functions, as shown below
From the table, we can see that aducm360 has the highest resolution, while ads4225 (ads4225 Data Book) as an oscilloscope application has the highest sampling rate. From the application results, we can simply summarize these points:
Oscilloscope is a high-speed system, which should deal with different signal acquisition, so it is suitable to use ADC chip with high sampling rate
The temperature measurement system is usually low-speed, so the narrowband ADC is more suitable (no waste of resources), but it is required that the ADC must have high resolution
Of course, in the actual product application, in addition to these two basic parameters, no code loss resolution and noise are important consideration indicators for ADC selection, which will not be explained one by one here.
From the above conclusions, we can also find that the electronic thermometer introduced at the beginning of the article is only the most basic temperature measurement scheme, and as long as the microcontroller with integrated ADC function is basically competent. And like ADI, aducm360 microcontroller integrates 24 bit high precision ΣΔ ADC belongs to the field of higher-end instrument level temperature measurement (of course, it is not limited to temperature measurement). If it is really only used as an ordinary electronic thermometer, it does catch up with the "chicken killing ox knife". Then, let's look back and see if the positioning of eval-aducm360mkz evaluation board will be clearer!
Eval aducm360mkz evaluation board
At the beginning of the article, we simply said that the evaluation board is like a "minimum system" based on ADI aducm360 microcontroller, but the actual evaluation board is really a complete temperature measurement reference scheme, isn't it incredible?
Let's take a look at the specific resources of the evaluation board, as shown in the figure below
The aducm360mkz evaluation board is powered by an external 5V voltage. The board card supplies power to the main microcontroller through an ADI 5V to 3.3V low voltage differential linear regulator. The board carries a PT100 (PT100 Data Book) RTD (resistance temperature detector) temperature measurement circuit. In fact, there are not many functions on the board.
PT100 is a standard of platinum thermistor temperature sensor. When the temperature is 0 ℃, the resistance value of Pt100 is 100 ohms. When the temperature increases, the resistance value of Pt100 will increase. For the specific temperature resistance relationship, please refer to the corresponding graduation table.
However, the evaluation board also leads to the expansion interface of microcontroller IO port. We can build a more perfect temperature measurement scheme according to the actual needs, such as adding K-type thermocouple, or adding Bluetooth module or WiFi module to form a high-precision intelligent temperature measurement scheme, We can also see many similar schemes in the market (of course, it may not have such a high-precision ADC), such as candy smart thermometer, pacifier thermometer, etc. the principle is basically the same, but it is applied in a more differentiated market.
The following figure shows a simple high-precision USB thermocouple measurement system based on aducm360mkz evaluation board: (next page)
Development and debugging
When it comes to development, everyone is no stranger. However, ADI seems to make development easier.
preparation
Open the supporting CD provided by Adi eval-aducm360qspz development kit (the information in the CD can also be obtained on ADI's official FTP < < need FTP download tool support >, and users can download freely), and you can see the corresponding ide tools and j-link drivers (as shown in the figure below)
After selecting the aducmxv1.3.exe executable file in the CD-ROM and installing it, you can get all the board and chip materials, start-up instructions, code routines and other resources provided by ADI. Is it more convenient and practical than searching and downloading on the Internet? Even friends who contact the development board for the first time can start to operate quickly.
Hardware debugging tools
ADI provides a supporting hardware development tool j-link ob, which supports non intrusive serial debugging and a UART communication interface (as shown in the figure below)
The interface of j-link ob adopts the 8pin interface design matched with eval-aducm360mkz evaluation board, and the design of jumping cap selection is also made on the signal line to facilitate the targeted debugging of engineers during actual development (its definition is shown in the figure below). From the introduction of official data, j-link ob can be completely used to replace the previous j-link Lite debugger.
Of course, the debugging of aducm360 is not limited to the j-link ob, but all the debugging tools commonly used in the industry. In addition to the power supply voltage and GND signal to the target board, the corresponding relationship between the data signal and the clock signal on the standard JTAG and SWD pins is shown in the figure below:
Integrated ide Tools & rich routines & elves
The biggest advantage of using Cortex-M3 kernel in ADI aducm360 microcontroller is that it is supported by a wide ecosystem, so the current third-party ide tools IAR and keil can be used (we can also see the ready-made installation program on the CD, which will not be introduced here). Moreover, ADI also provides quite rich code routines in these two IDE versions (as shown in the figure below)
However, I'd like to tell you about elves, another auxiliary development tool of ADI (it is provided in ADI CD (supporting FTP download tool), and another serial port download tool cm3wsd, which will not be introduced more)（ (next page)
If you want to evaluate the peripheral functions of a development board or microcontroller, what should you do? First of all, you must write a piece of corresponding code, and elves is a tool to generate a simple C function library. All engineers need to do is select the corresponding parameters for each function, and Elves will generate the corresponding C language source code that has configured the microcontroller register. Does it sound very mysterious?
Let's actually demonstrate that taking the Keil ide tool and UART function output as an example, the original code routine selects RTD_ Demo。
Open elves program, and the display interface is shown in the figure below. The specific operation steps are as follows:
① Select Add to add urtlib. H
② Select the function you want to generate
③ Set specific parameters
④ Then select Copy and paste to the original RTD_ By comparing the UART output function code in the demo routine (as shown in the figure below), it is clear that the code output by elves is indeed OK
Is it convenient? Elves' ultimate goal is to shorten the design cycle of engineers. If you think it is often needed, you can also add elves to the shortcut toolbar of the existing third-party IDE (keil tool as shown below, select tools - > Customize tools
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