Load management from COM or USB. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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We manage loads from COM or USB. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Computers

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The circuit is based on shift registers 74hc595, which are controlled by the PIC18F252 microcontroller. The circuit outputs are logical, i.e. log "1" or log. "0". They are low-power, so amplifiers (keys) are needed to control some devices. Do not forget about the galvanic isolation of controlled devices with the circuit! The controller is controlled by the USART protocol directly from the computer. Methods for implementing the protocol are discussed below.

Consider two ways to get USART.

1st, easiest way:

This is an RS232 to USART level converter. The diagram of which is shown below.

We manage loads from COM or USB. RS-232

I think there is nothing to tell here. 7,8 pins are connected to the COM port of the computer, and 9,10 to the main circuit of the device.

2nd way: USB to COM converter

Almost all new computers do not have a serial COM port, and most of the old equipment works through this interface, the so-called RS232. The USB serial bus has appeared on new computers, but the communication protocol via USB is more complicated than via RS232.

Thanks to the development of the English company FTDI (Future Technology Devices International), it became possible to convert USB into a "virtual" serial port, data exchange with which is carried out by the usual well-known methods.

This is a USB to COM interface converter designed to connect a modem, scanner, various measuring equipment via the USB bus, i.e. in fact, any device that previously used the RS-232 interface. Moreover, the user does not need any knowledge about the device and the operation of USB. The software drivers supplied by FTDI give the impression that the communication is going through a regular COM port. Of course, this is only true if the software uses the COM port in standard mode.

Schematic diagram of the interface converter is shown in the figure. Its basis - the DD1 FT232BM chip is included according to the standard scheme recommended by the manufacturer.

Manage loads from COM or USB

The DD2 AT93C46 EEPROM chip can be omitted. It stores the manufacturer's identifiers (VID) and personal (PID), the serial number of the product and other data. This is necessary if several devices based on FT232BM chips are simultaneously connected to the computer via USB. The serial number is especially important, since the software driver relies on its uniqueness, associating one or another virtual COM port with a specific device. If there is no ROM, only one device forming a virtual COM port can be connected to the computer. Instead of AT93C46, you can use AT93C56 or AT93C66. The ROM is programmed directly in the device using a special utility supplied by FTDI.

Manage loads from COM or USB

I shortened the schematic a little and did it like this. Power made from the general circuit of the device.

Manage loads from COM or USB

RX and TX pins to the main circuit of the device. The driver for this MS can be downloaded from ftdichip.com for a specific OS.

The operation of the device is a two-way communication with a PC at a speed of 115200 Kbps. with command checksum verification. Those. erroneous data transmission is excluded. When the program starts, it polls for the presence of a connected device, and if it is found or lost in the process, the program will let you know.

This device is controlled by a program specially written by me and lies in the archive. In principle, the program, as it were, is a demonstration program, it can only control the outputs. So for an individual program, for a specific case, please contact us.

The archive contains a program for a PC and a demo firmware for the MK device. Firmware on PIC18F252 for a specific PC is original, to get it, write to me. Demo firmware works for 10 minutes, then the MK must be re-flashed.

In general, everything seems to be. Any questions, please write.

Download archive (87 kb)

The author accepts orders for the development of devices based on MK

Author: Alexey Klyushnikov Ivanovo, al.kl [dog] mail.ru; Publication: cxem.net

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