Microsecond stopwatch output

Discussion in 'The Projects Forum' started by Jragon, Dec 11, 2015.

  1. Jragon

    Thread Starter New Member

    Sep 29, 2015
    Hi There,

    Currently I am making a microsecond timer (it will later be integrated with opto-isolators to make a physics light gate). Currently my design is to use seven segment displays. This is the circuit diagram (I haven't put all 8 seven segment displays in, it also goes in the wrong order: least significant to most):


    I would like to use the HDSP-2131 chip (or equivilent) to output the timer's numbers. So onto the issue:

    The HDSP-2131 uses a 4 bit address line to pick which display you will change when it clocks. I'm not sure how to connect all the outputs of the 8 counters (normal binary counters which reset on 10) to the data lines (D0-D3) and then have the address correspond to right digit when it clocks.

    Here is the pin diagram for the HDSP-2131:

    I would connect the outputs of the counters to D0-D3.

    I think I understand how I would do it with a microcontroller if the timer was in miliseconds instead (the microcontrollers I have have a 1MHz clock).

    Sorry for the poor quality of communication!


  2. Papabravo


    Feb 24, 2006
    You seem to be of the opinion that only one digit at a time changes. How are you going to handle the problem of having multiple digits changing on each clock, including possibly all of them simultaneously? Also, shouldn't the design be synchronous, with a separate method of updating the display. Are you going to use the onboard character generator or were you going to output the actual pixels for the characters of the numbers? It is not clear to me that you have thought out this design very carefully.
  3. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    That will not work. The display has 8 data lines, not 4, and can display the full ASCII character set. Characters start at 20h, and numerals start at 30h, not 0h. This indicates that you did not read, or do not understand the datasheet description of how this part operates. IF you change to BCD counters and AND IF they have tri-state outputs, THEN it is possible to do what you want by designing a data scanning system to poll your counters constantly and update the display. But at that point you have doubled the complexity of your timer electronics compared to what you have now. How badly do you want to use that display?