Intelligent transformer temperature monitor circuit module design

A company is given to ATMET 89C51 microcontroller core temperature intelligent monitor, monitor with automatic temperature recording a three-phase power before phase, a record
Intelligent transformer temperature monitor circuit module design - schematic

high temperature and other data and black box function. 89C51 microcontroller is ATMETs 8-bit Flash microcontrollers, the biggest feature is the on-chip containing 4KB re-programmable Flash memory, 128 8B internal RAM and two 16-bit timer/counter, in the development process is easy to modify the program and is compatible with MCS-51. For LED control driver, use PS7219, and its interface with synchronous serial peripheral interface (SPI), can drive eight digital control (using one of five), because having 15 8RAM PS7219 internal function control register, easy to find address of each digit individually controllable refresh the display brightness can be CNC, each with a flashing light to enable full control and functional testing, which simplifies hardware design, CPU port line savings and reduction occupy CPU time. Because the work status settings, parameter settings and other key composite keyboard the way, thus has fewer keys, keyboard keys are designed as standalone interface through level detection input lines can easily determine which key was pressed. Communication with the host meter using MAX232 chip, this chip has a dual driver/receiver, chip contains a capacitive voltage generator to provide EIA/TIA-232-E level on a single supply each a receiver to EIA/TIA-232-E level input is converted to 5V TTL/COMS level, there are some special instruments need to save the data, the preparation of EEPROM circuit design and power monitoring circuitry to achieve the above functions. Output driver circuit ULN2003 drive, this chip has seven Darlington, the collector can collect a maximum current of 500mA, due to internal connected with freewheeling diode can be driven relay inductive load. Preamble signal processing circuit : CD4052 is 4 to 1 multiplexer dual analog switches, which are four groups input three-phase winding temperature signal and the ambient temperature signal 3-way (optional), switching between these signals by the program through the microcontroller the port line control. Because the detected temperature signal is a slowly varying signal. In order to effectively improve the anti-jamming capability of the instrument, so be RC low-pass filter. In order to increase the input impedance and high common-mode rejection ratio, the first preamplifier stage using differential connection, R4, R5, R6, R7, R8, R9 resistance should be carefully selected to match the two pairs, and the selection of micro amplifier drift, low offset, high-gain high common mode rejection ratio of the chopper-type auto-zero op amps TIL7650. Level 2 inverting amplifier magnification by RW2 multi-turn potentiometer adjustment.

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