In this Instructable we are going to control a 7 segment LED displaywithout using a Microcontroller (a Microcontroller less Display) and Display alphanumeric characters on it.
Here we are going to use a FT232 USB to Serial Chip to interface a Common Cathode 7 segment display with your Windows PC .The software running on the Windows PC will control the 7 Segment Display using D2XX library and Display characters on it .
The Software code is written in ANSI C and uses the D2XX library from FTDI.
If you are new to the D2XX library from FTDI, You can check this tutorial for more information.
Source codes, D2XX Library and Circuit Diagram can be Downloaded from here.
Step 1: Materials Required
For this Instructable you will require the following things
1) FT232 based USB to Serial Converter, Here I am using USB2SERIAL (USB to RS485/RS232/Serial Converter)
2) 7 Segment Common Cathode Display
3) 74LS244 Octal Buffer
4) Female Berg strip Connectors
5) USB cable
6) A Windows PC
USB2SERIAL (USB to RS485/RS232/Serial Converter) is available from our online store for purchase
D2XX library will only work with FT232 chips from FTDI International. The Program will not work with chips manufactured by other vendors (eg:-like TUSB3410 from TI).
Step 2: About D2XX Library
Key to this project is the D2XX library from FTDI. This Library helps us to program the FT232 chip and configure it's other modes.
We all know about the USB to Serial Conversion function of the Good old FT232,by using the D2XX library you can change the chip to a USB to Parallel converter. The other modes of FT232 are called as Bit Bang Modes.
There are 3 types of Bit Bang Modes (BBM)
1) Asynchronous Bit Bang Mode
2) Synchronous Bit Bang Mode
3) CBUS Bit Bang Mode
A detailed explanation of various Bit Bang Modes and How to configure them can be found here.
For Controlling the 7 Segment Display, we will be using the Asynchronous Bit Bang Mode
D2XX library along with the Source codes can be downloaded from the original article page.
Step 3: Asynchronous Bit Bang Mode
In Asynchronous Bit Bang Mode FT232 works as a USB to Parallel Converter with 8 bit wide ports. Here the DTR ,RTS ….RI along with TXD and RXD pins of FT232 works an 8 bit parallel port.
Here TXD acts as D0 bit (LSB) of the 8 bit Port and RI works as the D7th bit (MSB) as shown in the above figure. More information about configuring the Asynchronous Bit Bang Mode can be found here.
Please make sure that all the Pins mentioned above are available on your FTDI breakout Board .In the case of USB2SERIAL all the pins are easily available outside on male berg strips.
Step 4: Connection Diagram
Here the PC communicates with the USB2SERIAL Board using D2XX library .
The command send from PC are then used to control the 7 segment Display .
A 74LS244 buffer is used to protect the pins of FT232 from excessive current drain.
The Circuit Diagram of the LT543 Driver Board along with assembly instructions can be found here.