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Help choosing multiplexer for 10-segment LED

Victor Skulavik II
Prodigy 70 points
Other Parts Discussed in Thread: TLC5925, TLC5952

Hi, I'm a student working on a university robotics project and I need help choosing a multiplexer.

The basic idea:

I want to connect 4 data lines to a multiplexer such that I can output a binary number indicating how many LEDs I want lit and it turns the binary bits into x-number of lines to drive a 10-segment LED (http://parts.digikey.com/1/parts/681333-led-bar-graph-10seg-red-ylw-grn-hdsp-4832.html).

For example:

  • When I output "0101" (for 5), have 5 of the LEDs light up.
  • When I output "0000" then none of the LEDs will light.
  • When I output a number 10 or higher, all of the LEDs will light.

Now, I don’t care if the LEDs are biased high or low, but I just need an idea of how to connect them (I know just enough to know they need resistors on each LED). 

In my scenario, I need to use serial out data from the RB100 (http://www.roboard.com/RB-100.htm) using either TTL, SPI, or RS232; so help knowing how to convert serial data to the 4 parallel lines for the multiplexer would also be very much appreciated!

Thanks!

  • 0
    TI__Guru 66350 points

    Hello Victor,

    As far as I understand, you have a serial output that gives 0101 if you want to have 5 LEDs lite, right?

    If you have a look on TLC5925, you can see that this part has a serial interface, therefore you would not need a serial to parallel translation, you need just something that translates the 0101 to 0000000000011111. I wonder if your RB100 can directly send a 16 bit word serial instead of a 0101.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 70 points

    Brigitte,

    Thanks for the suggestion, that looks really cool! However, let me expand on my first post a little bit and see what you think...

    I want to use the serial-TTL (COM4 or COM3) of the RB100; it'll output serial data a-byte-at-a-time (8 data + control bits). I mentioned only 4 bits in my previous example because I'd like to have two 10-segment LEDs each controlled by the low and high nibble, respectively, of a single-byte output from the port.

    For example, when I output "6A" (which is "0110 1010") to the port, I want one of the LED packages to light six of it's LEDs, and the other LED package to light all of it's LEDs.

    Can you explain to me how the TLC5925 processes multiple-bytes of serial input?

    If there is something similar to the TLC5925, but with 20 output pins (or perhaps 24 outputs - 3 bytes), that would work and I could just translate the bit-conversions in software...

    Thanks for your help!

    - Victor

  • 0 in reply to Victor Skulavik II
    TI__Guru 66350 points

    Hello Victor,

    Please have a look on TLC5952. This part has 24 channels.

    Serial Input:
    Have a look on page 12, Figure 9 in the datasheet. There the timing diagram is given. You input 24 bits of data (turn LED on or off) or brightness control into the serial input and then latch this data into one of the latches with the LATCH input.

    So using the COM port as is is maybe not possible. But in general almost all processors should be able to generate a bit stream out of a hex word. I really do not know about a hardware solution which is doing this. For such a solution you might ask the interface forum or the university zone forum.

    Best regards,
    Brigitte