3 Replies Latest reply on May 11, 2015 4:47 PM by abdurrachman.mappuji

    7 segment LED and 7 segment LCD


      cy8ckit-049-42xx, last PSoC 3.2 beta.


      I need to drive more than one 7 segment LED display: every digit has a common cathode, 8 segment lines shared bertween all the digits. I want to implement operational mode, when the only one segment is active at the every moment of time. this means, that PSoC should connect first cathode and light all the segments in sequence if it is necessary, then next cathode will be selected and procedure will be repeated. Additionaly i want to implement brightness PWM management. Having stable frequency of the segments activation, I can change the time of the period, when segment is really ON.


      I've found a standard component, which can drive an LCD display. One of the possible configurations can drive 7-segment LCD display with more than one digit.  It is doing something like I need, but the LCD has different operation principles (Vdd/3 <-> 2Vdd/3 levels, mean voltage 0 & etc.).


      The question is following: can I use this LCD component and just connect my LED instead of LCD. How many segments will light at the same time, will brightness management work in my case?


      I've checked already this site for solution, but didn't found anything interesting: PSoC 4 has no DMA - the standard component to drive LED displays doesn't match to my setup. I've tried to implement my own controller already, but It takes almost all the UDB's my PSoC has. 

        • 1. Re: 7 segment LED and 7 segment LCD

          You will need a timer and an interrupt to switch between the digits at about 50-100Hz * Number of digits.


          A PrISM component for brightness controll


          An LUT with 5 inputs(4 bit number, 1 bit PrISM) and 7 outputs


          A Control register to keep the actual digit value connected to the LUT


          7 pins for driving the Rs connected to the segments fed from the LUT


          (Number of digits) pins to drive the digit-select hardware which will be a simple NPN


          In the interrupt handler you increment a digit counter, de-select the current digit line, update the control register with new number and select new digit line.


          Seems to be straight forward.





          • 2. Re: 7 segment LED and 7 segment LCD

            Here is a possibility -








            Regards, Dana.

            • 3. Re: 7 segment LED and 7 segment LCD

              Hi pavuk, i think you need an extra component to do your project (for multiplexing) and also you can use LUT to simplify your program. About using LCD component i dont know about the possibility, but i know that 7-segment is far different with LCD, maybe the dot matrix is close enough to Character LCD.