ADuC831 DS1921G AD8203 Datalogger Circuit

Data logger project ADuC831 Datalogger Circuit data measurement in processes and followed by a microprocessor equipped with a datalogger based on one from the economical I51 series microcontrollers. Data logger control was implemented via RS232, RS485 or USB interface. The Datalogger is equipped with analog modules for temperature and atmospheric pressure measurements. The measured data is stored on the SD card files that can be processed on a computer. The datalogger can be powered by a voltage battery at least 5.5 V. The used parts, including their parameters, are described in the thesis. Further the thesis deals with the description of circuit design and software for the microcontroller and PC.

Temperature recorder DS1921G Thermochron iButton This miniature clock battery serves to record the temperature. It contains an internal lithium battery and is perfect for use to record long-term temperature. When setting the maximum interval between individual logs can record values for almost a year (362 days).

Analog Devices ADuC831

The processor is the most important part of the datalogger. If it is large enough internal memory into which you can write during program run, and has an A / D converter, then can itself serve as datalogger. If we decide not to use the outside AD converter, then you need to select a microcontroller containing an AD converter, which has a sufficiently large resolution, is sufficiently fast and accurate. Another
demand is low consumption, for example, with sleep mode microcontroller, in which the stream is discharged in the order of units or tens microamp. RS232 should be used for communication, so it is advisable use a UART. Because I chose an SD card for data recording, which I must have power supply 2.7 – 3.6 V, the hardware will be easier if the microcontroller is to support the same voltage. At this voltage they have microcontrollers less power consumption, which will also increase battery life. After considering the previous requirements, the ADuC831 microcontroller was selected by Analog Devices.

Real Time Clock PCF8583

Real-time clock saves a large amount of battery power because it is possible
thanks to them, the microprocessor snooze and turn off all the peripherals until it is given
time. At the same time, after setting the carrier, the current time and date. For this function he was
the PCF8583 is selected.

SD Card from SanDisk with 2GB capacity The SD (Secure Digital) card is memory based on the flash EEPROM. SD card has been developed to safely store consumer electronics audio and video data. Card communication is via a 9-pin interface consisting of a clock pin, for selecting data or command communications, four pins of data and three feeds.

To connect a data logger to a PC, you need to use the converter because most computers does not have an interface that can be directly connected to a microcontroller. The RS232 connection to the COM port is common computers. However, the RS232 is not compatible with the microcontroller voltage, so we have to use a TTL level converter to RS232. Because the supply voltage of the microcontroller is 3 V, we use a converter that can be powered from this relatively low Tension. For example, this is a MAX3232ID converter. To get the tension

MAX485 CONVERTER

For connection of devices in environments with high electromagnetic disturbance or it is not a good idea to use the RS232 line for a long distance. It uses it voltage levels that can change over long lines. RS232 would therefore should not be used at a distance of more than 15 m, where there is an increased risk incorrect transmission. The RS485 uses a pair of wires that are wired in a counter phase for data transmission and the receiver evaluates the voltage difference. This makes galvanic department and line is capable of transmitting data between devices with different potential. Therefore, the line can be up to 1600 m long. RS232 also supports communication

A FT232R circuit from FTDI is used to convert USB to RS232 A chip that can convert the communication between one capacitor and one capacitor USB and RS232 bus.

PT100 CONNECTION

There are specialized circuits for measuring temperature using Pt100 or Pt1000, such as AD70 from Analog Devices, but they are in the Czech Republic difficult to access and therefore expensive. The AD70 would be an ideal solution – it can be powered voltage 5 V, integrated current sources and voltage reference. With this the accuracy of the circuit is greater than 1 ° C.

Standard analog inputs are 0 to 20 mA, 4 to 20 mA and 0 to 10 V. Company Analog Devices produces AD8203, which can be used as a converter current to voltage. AD8203 works as a differential converter, it can also be used as a 0-10 V voltage converter for voltage ranging from 0 to 2.5 V. Unfortunately, it is also unavailable in the Czech Republic. That’s why it was designed again connection from available components. Therefore, standard inputs will be processed re-used TLC271 operational amplifiers. These amplifiers are connected as voltage amplifiers and resistor values are selected so that the output is as close as possible range 0 – 2.5V.

PRESSURE SENSOR MPXH6115A Measurement of atmospheric pressure can serve to predict the weather, but also to determine the height of airborne vehicles above the terrain.

THERMISTOR NTC 2322 641 10 K Temperature can also be measured using a thermistor. Thermistor is a component whose resistance the temperature changes more than that of metal temperature sensors. The measurement is not therefore need to use bridge connection.

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