Production of Internet Timer Based on PLC

ADSL is the most widely used broadband access method. Many users use ADSL

The routing function of MO-DEM enables multiple computers with PLC-based Internet timers to share Internet access to reduce Internet access fees. For the various tariffs provided by network operators, there are Internet access time issues except for users who use monthly packages.

Generally, the Internet timekeeping is realized by computer timekeeping software. These software are all for single computers that access the Internet by dialing. There is no good timekeeping method for using the routing function of ADSLMODEM to realize the sharing of Internet access by multiple computers. Because when ADSLMODEM works in routing mode, as long as the MODEM power is turned on, the MODEM will automatically dial up to connect to the network. Therefore, to calculate the Internet time, the power-on time of ADSLMO-DEM must be calculated.

The author used PLC to make an Internet timer device to monitor and control the shared Internet time.

Now let's take the example of two computers in a small office sharing the Internet. The standard is 240 hours per month, and the usage time is set from 8 am to 24 pm.

2. PLC wiring

Schneider's NEZATSX04CD06R8A small PLC (with clock function) and IHMI are used here

TSX08H02M two-line Chinese text display. PLC wiring is shown in Figure 1, the power supply is AC220V. ADSL

The power supply of the MODEM is controlled by the output contact Q0.0 of the PLC, the alarm output is controlled by the Q0.1 of the PLC, and the start time is controlled by the input contact 10.0 using a double-control switch. The two switches are installed in two offices with computers and are equipped with corresponding working indicators. When 10.0 is connected, if the conditions are met, Q0.0 is connected, so that the two offices can turn on or off ADSL according to their respective Internet needs.

The power supply of the MODEM is DC24V. It is connected to the PLC through the TSX08HMRUNCAB cable and the NEZA TSX04CD06R8A

The PLC communicates via the default communication protocol, and the daily and monthly available time is set via the HMI.

3. Programming

The main function of the timer is to control the Internet time to no more than 240 hours per month, that is, the average daily usage time is no more than 8 hours. The two computers are connected to the Internet as needed, and the Internet time periods and times are basically irregular, which may be staggered or overlapped; sometimes it may be used for more than ten hours a day, and sometimes only one or two hours a day. In order to reasonably control the Internet time, the Internet timer should have the following functions:

1. Accumulate the Internet time of the day and display it on the HMI, reset every 24 hours. The reset time is set to 8:00 a.m.; 2. Accumulate the Internet time of the month, and calculate the average daily usage time of the month (the cumulative number of Internet hours of the month)/(the number of days that have passed in the month) and display it on the HMI, reset once a month, and the reset time is 8:00 a.m. on the 1st of each month; 3. If the usage time of the day is greater than 8 hours, an alarm will be issued, but it can still be used; 4. If the usage time of the day is greater than 8 hours, and the average daily usage time of the month is also greater than 8 hours, the PLC will cut off the power supply of the MODEM and the Internet cannot continue; 5. Display the remaining hours of Internet access in the month.

The partial PLC program ladder diagram designed according to the above requirements is shown in Figure 2.

PLC has a clock function. Through the PLC scheduling module, the allowed working time is set from 8 am to 24 pm, and working is prohibited at other times. Call system word %SW50-%SW53 to display the current time and date. The reset function at 8 am every day is realized by calling system word %SW51, and the reset function at 1 am every month is realized by calling system word %SW52. Since PLC only provides minute pulse signals and the maximum preset value of the counter is 9999, 240 hours per month (14400 minutes) has exceeded its preset range. Therefore, it is necessary to build a 10-minute time base generator to calculate the monthly cumulative online time, that is, 240 hours per month is converted into 1440 10 minutes, and the maximum cumulative time per day does not exceed 1440 minutes, so %S7 (minute pulse signal) is still used as the counting time base. In order to facilitate user observation, the values ​​calculated by PLC are converted into *** minutes and *** ten minutes when they are sent to HMI (text display). The engineering quantity conversion function of the HMI configuration software is used to convert them into the format of *** hours and *** days.

4. Instructions

Enable ADSL

The routing function of the MODEM is used to connect several computers that want to access the Internet with a five-port HUB (Ethernet hub) and perform relevant configurations to form a small local area network. Close either of the double-control switches, the output contact Q0.0 of the PLC is connected, and the ADSL

The MODEM is powered and connected to the network. The HMI displays the current date, the accumulated online time of the day, the accumulated online time of the month, and displays the remaining online time of the month in a countdown manner. If the online time exceeds the set time, the alarm light flashes (the alarm light flashes once per second for one minute) or the MODEM power is cut off, and the HMI will display the cause of the error.