Driving A 7 Segment LED Display From An FT232

Sometimes, a good hack is about using less rather than more. That’s the case with this neat tutorial from [Rahul.S] on driving a 7-segment LED display with an FT232. By using this cheap USB to serial controller, [Rahul.S] was able to drive the display directly without using a microcontroller, which keeps the component cost down.

He’s bit banging an octal buffer connected to the display. You may be surprised to find that the FT232 chips do have enough outputs to make this work. Rather than send serial data number to the display and have a controller convert this into a set of signals that make the number, this conversion is done by the PC, which then sends a signal that directly illuminates the appropriate parts of the LED. By using all of the available output lines of the FT232 (including ones like the RTS/CTS line that are usually used for signalling), [Rahul.S] was able to drive all seven of the elements and the decimal point.

Of course, cynics may argue that it would be simpler to use a cheap serial LCD display. That is true, but there is always something to be said for knowing how to do something yourself rather than letting others do it for you…


9 thoughts on “Driving A 7 Segment LED Display From An FT232

  1. What about using a Microchip MCP2200, which is a USB-UART chip including 8 GPIO controllable by HID-USB interface?

    Not only is cheaper than the FT232RL ($2.33 vs $4.50 on digikey), but also you don’t need the octal buffer.

  2. This is just the beginning. There is a very nice IC from TI, with this you can drive upto 64 Outputs with just the data signal of every USB-Serial-converter, using nothing but the usual serial data line und without abuse of any controlsignal or need for special drivers on the computer side.
    Just use the SN74LV8153 and send it 2 Bytes for every 8bit Output. You can address up to 8 of this beauties.
    The data format is absolut simple
    Startbit + LSB Bit High + 3 Adress Bits + Lower Nibble + Stop
    Startbit + LSB Bit High + 3 Adress Bits + Upper Nibble + Stop
    The Baudrate can be between 2 and 24kBaud and will be autodetected.

    There are a few other nice features…
    Outputs selectable between Open collector and push-pull. With voltages between 3 and 12V.

  3. You can find videos of guys opening a beer with a bulldozer, but it doesn’t mean it’s the best and most cost effective way to do it. For the price of FT232 chip you can buy Microchip or Atmel micro that has native USB interface, or if you want to save some money you can use V-USB or such thing. But since this is hack dedicated site I appreciate seeing one more way to drive things via serial port, so thumb up for [Rahul.S].

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