Provides cost-effective AT89S51 analysis solutions for multiple embedded control application systems

The system hardware configuration is based on the AT89S51 microcontroller. The AT89S51 is a low-power, high-performance CMOS 8-bit microcontroller, which contains a 4Kb ISP (In-system programmable) Flash read-only program memory that can be repeatedly erased and written 1,000 times. The device is manufactured using ATMEL's high-density, non-volatile storage technology, is compatible with the standard MCS-51 instruction system and 80C51 pin structure, and has a built-in watchdog (WDT) circuit.

The powerful AT89S51 can provide cost-effective solutions for many embedded control application systems. The punch press controller designed with this single-chip microcomputer has the following features:

Figure 1 Hardware block diagram of the controller

● The controller adopts the PLC design concept, with high reliability and strong anti-interference ability.

● The 6-digit seven-segment LED display on the panel can be used to adjust parameters and display count values ​​during operation.

● Modular design, compact size, easy to install.

● Taking advantage of the ISP function of AT89S51, programs can be downloaded on-site to realize the functions of a programmable controller.

Hardware Design

The hardware structure of the controller is shown in Figure 1. It mainly consists of keyboard display circuit, EEPROM circuit, power-off detection, program download interface, photoelectric isolation input and output modules. The power supply module is a switching power supply designed with TOP220Y with +24V and +5V output. When the system is powered off, the power-off detection circuit sends a signal to AT89S51, and the system immediately stores the parameters and count values ​​in the EEPROM circuit.

The keyboard display circuit is shown in Figure 2. In order to save I/O port lines, the lower 3 bits of P0 port are reused here. The working principle of the circuit is introduced below: When displaying, first set P3.3 and P0.0~P0.5 to high level, and then output the code corresponding to the display content to the common cathode digital tube through the serial input and parallel output shift register 74HC164 in turn, and then set the bit selection to be displayed to low, delay 1ms, and then set the bit selection to be displayed to high. As long as the frequency of this dynamic scanning is high enough, this controller uses 80Hz, due to the visual persistence characteristics of the human eye, the display function can be realized without flickering. When scanning the keyboard, set P3.3 to low level, then the output of 74HC164 is all low level, which prevents interference with the display when scanning the keyboard. When no key is pressed, the read P0.0~P0.2 are all low level. When a keyboard is pressed, the corresponding input will be read as high level. Then, the delay de-jitter method can be used to determine which key is pressed, and then go to the function program of the corresponding key. The display scanning, keyboard scanning and key debounce of this controller are all completed in the timer interrupt.

Figure 2 Keyboard display circuit structure schematic diagram

The photoelectric isolation input circuit is shown in Figure 3. The input terminal and the COM terminal are connected with a voltage-free contact or an NPN open collector transistor. For reliability, the input current is 7mA, then the input is ON. When the input current is lower than 1.5mA, the input is OFF. The output circuit uses a photoelectrically isolated relay output to electrically isolate the internal circuit of the controller from the external circuit to prevent external interference.

Figure 3 Photoelectric isolation input and output circuit [page]

Specific applications

The punch press control wiring is shown in Figure 4. When working, the 6-digit digital tube on the panel displays the count value. When you need to set parameters, press the function key for 5 seconds to set the single action duration, the number of times lubrication is required, the lubrication duration and other parameters in turn.

Turn the selector switch to the single stroke position. When the slider is within the upper dead center range, press the left and right buttons at the same time, then the double valve is energized and the slider reciprocates once. When the cam turns to the braking position, the controller de-energizes the double valve and stops the slider at the upper dead center.

Figure 4 Punch control wiring diagram

When the selector switch is in the inching position, press the left and right buttons at the same time, the controller will energize the double valve and move the slider. Release the buttons and the controller will de-energize the double valve and the slider will stop immediately.

Summarize

The punch press controller designed with AT89S51 microcontroller described in this paper has been tested and run reliably and has strong anti-interference ability. It can effectively prevent the punch press from continuous punching and ensure the safety of the operator by coordinating with software algorithm design and photoelectric protection. In addition, AT89S51 microcontroller has unique advantages such as rich instruction system, compactness, low price, flexibility and easy expansion, which greatly improves the cost performance of the whole system in the designed punch press controller.