"For toxic gases, everyone's first idea is to" avoid ". However, contrary to their wishes, it really exists in our daily life and will trigger this" minefield "accidentally. For the general public, toxic gases exist in coal gas, incompletely burned briquettes / natural gas, etc; For some workers who work in chemical enterprises all year round, the emission of toxic compounds and toxic gases involved in the industrial process is more common, and inadvertent leakage may threaten their health and even life at any time. Therefore, it is very necessary to have a toxic gas detection device in these places, which can let people know whether the concentration of toxic gas has reached the dangerous level at any time, so as to prevent accidents. Today, aiban.com recommends a low-power and portable carbon monoxide toxic gas detection scheme based on electrochemical sensor - ADI eval-cn0234-sdpz circuit board (click here to buy this development board on ADI's official website).
ADI activity recommendation
ADI cn0234-sdpz development board application for trial
Award winning Knowledge Q & A: defending life -- questionnaire survey on ADI low power and portable toxic gas detection solutions
ADI eval-cn0234-sdpz unpacking
Eval-cn0234-sdpz circuit board adopts the simple and environment-friendly packaging style with distinct ADI logo. The accessories in the packaging box include eval-cn0234-sdpz circuit board, adapter board, co-ax carbon monoxide sensor, software / data CD and an instruction for use.
The carbon monoxide sensor is packaged separately and uses the electrochemical carbon monoxide sensor of alpha company.
Electrochemical sensors can provide many advantages for instruments detecting toxic gas concentration, and most sensors are designed for specific gases. The available resolution is less than one millionth of gas concentration and the required working current is very small, so they are very suitable for portable power supply instruments. The parameters of this CO sensor are as follows.
The principle of the CO sensor in this paper is to allow the gas to diffuse into the sensor through the film and interact with the working electrode (the specific principle can refer to the circuit description provided on the ADI official website). The sensor and the development board are in-line connected and can be plugged in and out, which is very convenient. Perhaps considering that the circuit can be slightly adjusted to adapt to different kinds of sensor schemes in the later stage.
ADI eval-cn0234-sdpz hardware
The eval-cn0234-sdpz circuit board can be separated from the adapter board. They are connected through a 10PIN expansion interface, as shown in the figure below. It can be found from the schematic diagram that the main signals of the 10PIN interface include power supply, GND, SPI and I2C. It is confusing here. These signals are expanded with an adapter board, but the adapter board is only an adapter board, It doesn't make sense to "follow" these signals without a subsequent board. What's going on?
Let's sell a small pass here. Let's first understand some functions of eval-cn0234-sdpz circuit board, and then judge whether there is something missing in the whole set of carbon monoxide detector device?
Recommendations for ADI sensor development board:
ADI WSN accelerometer sensor development board It can easily add remote detection and monitoring capability to its products through scalable wireless network, and apply humidity, optics and temperature
ADI aducm360 uctrl temperature sensor development board A low-power, fully integrated 24 bit data acquisition system integrates dual core, high-performance development board on a single chip.
ADI adxrs453z position sensor evaluation board An angular rate sensor (gyroscope) for stable applications in industry, instrumentation and high vibration environment.
Eval-cn0234-sdpz motherboard is very small, but not exquisite. The PCB adopts a common 4-layer board design, the upper and lower layers are signals, and the middle two layers are power supply and stratum respectively. In terms of power supply design, eval-cn0234-sdpz can supply power through two AAA batteries or through external power interface. It supports 2.5 ~ 5.5V voltage source. The specific power supply mode can be switched through on-board power switch.
In addition, the special place is that the eval-cn0234-sdpz circuit board also leads to the expansion interface compatible with aducf101 wireless RF board card (sub GHz wireless technology, evaluation article: Building Automation / industrial field reform - ADI wireless sensor network development kit ev-adrn-wsn-1z evaluation), which can realize signal acquisition and transmission through wireless mode, This fully considers the possibility of various application needs on the market. The portable or wireless detector scheme is very considerate.
On the back of the eval-cn0234-sdpz circuit board, we can understand the whole power supply scheme of the board. The design of the power supply part of the board fully considers the safety and low power consumption: firstly, the reverse connection protection circuit of MOS transistor is designed at the power input end of the board; Secondly, in addition to two AAA batteries, the board also provides external input power supply, which is due to the step-down / step-up DC / DC regulator adp2503 adopted by the board.
(the circuit diagram is for reference only, and the device label may be different from the real object. For details, please refer to the schematic diagram officially provided by ADI)
Adp2503 is ADI's own step-down / step-up DC / DC regulator product, which supports an input voltage of 2.3V ~ 5.5V and an output voltage of 2.8V ~ 5.5V. At present, the on-board output voltage is designed as 5V output. From the official specifications, the characteristics of adp2503 are as follows:
Support 600mA current output
Switching frequency: 2.5MHz
Quiescent current: 38 μ A
In addition, this series also has a similar product with the model of adp2504, which can support greater 1A output current. Other characteristics are consistent with adp2503. Engineers in need can go to ADI's official website to check the device specification for detailed parameters (adp2503 / adp2504).
Recommendations for ADI sensor development board:
ADI WSN accelerometer sensor development board It can easily add remote detection and monitoring capability to its products through scalable wireless network, and apply humidity, optics and temperature
ADI aducm360 uctrl temperature sensor development board A low-power, fully integrated 24 bit data acquisition system integrates dual core, high-performance development board on a single chip.
ADI adxrs453z position sensor evaluation board An angular rate sensor (gyroscope) for stable applications in industry, instrumentation and high vibration environment.
The 5V voltage output by adp2503 regulator is inductively isolated and supplied to the analog acquisition front end of eval-cn0234-sdpz circuit board to avoid unnecessary interference. From the schematic diagram of circuit board officially provided by Adi, the analog front end acquisition circuit of eval-cn0234-sdpz circuit board includes reference voltage source Adr291, dual channel micro power amplifier ada4505-2, 16 bit ADC ad7798, refer to the following schematic diagram.
Adr291 (specification) low noise, micro power consumption, precision reference voltage source (2.5 V)
Ada4505-2 (specification) dual channel 10 μ A. Rail to rail I / O, zero input, crossover distortion amplifier
Ad7798 (specification) 3-channel, low noise, low power consumption, 16 bit Σ-Δ Type ADC, built-in on-chip instrument amplifier
(the circuit diagram is for reference only, and the device label may be different from the real object. For details, please refer to the schematic diagram officially provided by ADI)
The input voltage of adr291 is provided by the 5V voltage stabilizing source output by Adi adp2503 regulator, and the output 2.5V reference voltage source is provided to the dual channel micro power amplifier ada4505-2. As we all know, portable measuring instruments like this attach great importance to the battery life, so many engineers will consider low power consumption as the primary goal. In typical low power consumption tests, it is usually measured once, and then the system enters the standby state. However, in this circuit, the time constant of electrochemical sensor is very long, Therefore, the measuring circuit must be powered on for a long time. In this circuit, because an important characteristic of the electrochemical sensor itself is slow response, a dual channel micro power amplifier ada4505-2 can be used to reduce the power consumption during the operation of the circuit (the CO detection principle can refer to the official circuit description).
Ad7798 is a 3-channel, low noise, low power consumption, 16 bit Σ-Δ Type ADC, a high-precision ADC with built-in on-chip instrument amplifier, but the author doesn't quite understand it when it is used in the current circuit. I really think some are overqualified. Is it just to improve the accuracy? Perhaps a more affordable 12 bit ADC product is more suitable for this portable device.
In addition, in the eval-cn0234-sdpz circuit board, we know that the 16 bit ADC ad7798 is used to digitize the output voltage. However, from the specifications of the ad7798 and the official schematic diagram, the ad7798 finally outputs data through SPI signals, which are connected to the on-board 10PIN connector interface, but from the eval-cn0234-sdpz circuit board, This is the end of the circuit. This does not conform to a complete circuit. It should also need a master control board, which explains why there is an adapter board in the kit at the beginning. On the basis of eval-cn0234-sdpz circuit board, we also need a master control board for verification and evaluation.
Eval-sdp-cb1z main control board
ADI is officially equipped with a set of main control evaluation platform eval-sdp-cb1z main control board for eval-cn0234-sdpz circuit board, which is the control board of ADI's own system demonstration platform, as shown in the figure below.
Eval-sdp-cb1z main control board card characteristics:
Blackfin Processor adsp-bf527
USB 2.0 interface, connected to PC
JTAG interface
32MB SDRAM
120pin connection base * 3
Configurable peripheral interfaces: SPI, sport, I2C, GPIO, timer, etc
Since this article focuses on the eval-cn0234-sdpz circuit board, eval-sdp-cb1z is only used as the main control debugging board and will not be introduced in detail. Interested friends can visit the ADI official website for details.
Cooperate with the eval-sdp-cb1z main control board, connect through the adapter board, and then communicate with the computer. In addition, cooperate with the software environment provided by Adi, which is a complete set of carbon monoxide detection device system. The working hardware system block diagram is as follows.
Recommendations for ADI sensor development board:
ADI WSN accelerometer sensor development board It can easily add remote detection and monitoring capability to its products through scalable wireless network, and apply humidity, optics and temperature
ADI aducm360 uctrl temperature sensor development board A low-power, fully integrated 24 bit data acquisition system integrates dual core, high-performance development board on a single chip.
ADI adxrs453z position sensor evaluation board An angular rate sensor (gyroscope) for stable applications in industry, instrumentation and high vibration environment.
Compatible design scheme of eval-cn0234-sdpz circuit board
However, can such a carbon monoxide detection device really be called a low-power and portable application product?
Of course not! The hardware system scheme provided by Adi only allows engineers to better realize product evaluation and provides a general direction of hardware combination. The hardware scheme we really need to apply to the product still needs engineers to adjust and DIY according to their own needs. Just like the compatible design made on the eval-cn0234-sdpz circuit board, in fact, the set of CO detection device provided by Adi itself provides the possibility of a variety of hardware combinations:
If you need a low-power and portable toxic gas detection scheme, you can replace the 16 bit ADC on the circuit board with a mixed signal microcontroller integrating ADC function. In this way, the main controller and analog-to-digital conversion function are also available, which not only simplifies the circuit design, but also saves the material cost. Why not.
Of course, if the high-precision toxic gas detection scheme is pursued, the adr291 can be replaced by the reference voltage source adr3425 with lower temperature drift of ADI, and the micro power amplifier ada4505-2 can be replaced by two single channel ada4528-1 operational amplifiers, which can greatly reduce the noise and improve the accuracy, but such a scheme has a defect that it will increase the power consumption, However, if what you need is a high-precision solution and you don't care about the increased power consumption, there is no doubt that this choice is more suitable. Moreover, from the schematic diagram officially provided by Adi, the circuit board itself has a compatible design of this solution, which can meet the needs of different engineers and is very considerate.
Eval-cn0234-sdpz power on
Basically understand the ADI eval-cn0234-sdpz circuit board. We cooperate with the eval-sdp-cb1z main control board provided by Adi to actually experience this set of carbon monoxide gas detection device. It should be noted that when connecting the physical drawing, connect the 10 pin connector on eval-cn0234-sdpz to the adapter board (pay attention to the connection direction), and connect the 120 pin connector of the adapter board to the con a connector on the eval-sdp-cb1z SDP evaluation board (pay attention to the con a interface). The reference example is shown in the figure below.
To realize the communication between the main control board eval-sdp-cb1z and PC, we need to install the supporting software and driver provided in the CD-ROM of ADI suite on the computer side. From the readme file, it can be seen that the software is suitable for 32-bit windows system, but it has been proved that 64 bit system can also be installed.
After the installation of SDP evaluation software and driver, connect the main control board and PC through USB,
You can see the driver of ADI system verification platform in the computer manager,
At this time, open the software. If the communication is OK, you can see the prompt of correct connection in the adaptation window of the software, and directly select select
SDP evaluation software is an electrochemical sensor monitoring software specially made by ADI for Co. the interface style is very simple, basically does not need learning time, and there is no difficulty in getting started.
Recommendations for ADI sensor development board:
ADI WSN accelerometer sensor development board It can easily add remote detection and monitoring capability to its products through scalable wireless network, and apply humidity, optics and temperature
Our other product:
