Help in the design of a simple persistance of vision toy

Discussion in 'The Projects Forum' started by racecar, Feb 20, 2010.

  1. racecar

    Thread Starter New Member

    Feb 20, 2010
    So for my first project in my intro to circuits class I decided that I want to make a very simple programmable persistence of vision device.


    The general idea is that I'll be using a very fast counter to count through address lines of two 2114's, these will then be displayed on 8 LED's (two 2114's will be needed so that you can have 8 outputs as opposed to 4). In my description I'll be referring to this as having only 4 outputs since the circuit will just have to be doubled in order to have 8 outputs.

    I would also like this to be semi programmable, with any luck the circuit will function as follows.

    The user will press a series of 4 keys, each corresponding to a letter of 4bit height and a width of 16 bits (16 address lines). Depending on the button pressed a demultiplexer will link a clock to one of two counters which will then count through the address lines that correspond to a letter. Since the counters I'm using count 16 (74ls191, count 0000-1111) each character will need to occupy 4 address inputs +1 other address input so that we can easily store 4 characters on each chip. (the letter A will say occupie A0-A3 and then will have A9 wired high, while the letter B will occupie A0-A3 with A9 wired low). The outputs of this piece of memory will then be transfered to another piece of memory (2114), once the user has input 4 characters this piece of memory will be flipped into the Read position and a very fast counter (count to 64) will repeatedly read off the first 64 address lines of this piece of memory.

    My only question thusfar is:

    First: Just after the demultiplexer I need a counter that will count 0000-1111 and then remain stationary at 0000 untill the demultiplexer runs the clock to it again

    I'm sure I'll have more as I begin to construct this circuit, also I accept that im still very much an amateur at this so if you have any suggestions to make this a bit more stream lined feel free to suggest them.
  2. BMorse

    Senior Member

    Sep 26, 2009
    It sounds as if you are over complicating a simple POV device, this can be done with a handful of passive components and a pic.....

    Here is my POV Clock #1 (Propeller clock that works on POV)


    Here is another.....


    and also a handheld POV that displays messages in the air when the person waives it in the air.... (Although I don't have any pics of it in "Action")


    The later is probably closer to what you want to build, it is handheld and portable, and the user can select from several messages by pressing a button, the mechanism for triggering the display is a mechanical switch from a pedometer...



    these POV devices are simple to make using a microcontroller.....

    here is a circuit schematic for a new one I am working on that will also have 2 extra LED's on the outer most parts of the display, so I can have a "border" on top and bottom of the messages when displayed.....
    Pic16F628A POV.png

    Using a Pic with ADC inputs can also be used in conjunction with an accellerometer to detect movement to trigger the display...... and you can always use the accelerometers input to change messages also, by detecting "gestures" from the user.....

    B. Morse
  3. MuSu

    New Member

    Jan 10, 2011
    Hi BMorse,

    The first picture of your POV digital clock looks really nice... I wanna try it... would you be able to help me with some details?