Another clock project...

Discussion in 'The Projects Forum' started by MJL, Jun 23, 2015.

  1. MJL

    Thread Starter New Member

    Jul 1, 2009
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    0
    I have five digit seven segment displays from work that were being trashed. They both appear to work. My interest was in making a clock out of one or both of them. So, I used my Google-Fu and got a number of ideas. Some sound more complicated (but more accurate) and some would be fairly simple. I also found that in a seven segment display, either all the anodes are common, or all the cathodes are common, and it sounds like it is better to have a common anode setup so the drivers can handle more power.

    Some pictures...

    One of the big ICs is a multiplexer data is here http://www.intersil.com/content/dam/Intersil/documents/icm7/icm7218.pdf Also I've checked the power output of the transformer, it is 7 VAC iirc, and 5 VDC after the rectifier. One of the "How-tos" I read used a zener to create a 60 hz pulse, and subsequent counters to divide it down. It sounds fairly easy, but using the multiplexer is the one thing I'm not sure about.

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    I know a little about electronics, and am willing to do some research and studying to figure it out, except that some things are not easily googled. (Like the multiplexer) I've been looking at the Arduino a little bit, and am not sure about that. It's going to give me more computing power than I need.
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,516
    1,246
    The display is intended to be controlled through an RS-232 serial port. The AY3-1015 is a UART and the MAX232 is an RS-232 I/O driver. The idea is that the 7218 is an 8-byte RAM, five of those bytes are loaded through the serial port with BCD data for the digits, and the 7218 handles converting that to 7-segment data, multiplexing the displays, etc. The exact protocol can be worked out by tracing the pcb traces and turning that into a schematic, or getting the original schematic from work. The pin connections between the 7218 and 1015 (and the datasheets) will give you the bit format to send to the display to show what you want. This is not a super-complex board to reverse-engineer, and since it is all discrete there is no microcode to guess at; you can do it with enough time and patience.

    ak
     
  3. MJL

    Thread Starter New Member

    Jul 1, 2009
    4
    0
    Thanks. Sounds like it is going to be a bit of work to use it as-is.
    I spent some time at work the other day looking at dividers, counters, and such. I'll get a pic of what I have so far.
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
    1. Follow the original design to use the RS232, you need to try the communication mode as 9600,o,7,1.
    2. You can just using the display unit and using another uC or arduino to control the display unit.
     
  5. MJL

    Thread Starter New Member

    Jul 1, 2009
    4
    0
    Considering that I have little knowledge of what I am doing, is the RS232 the little three prong data port? I think they are labeled In, Out, and Ground? I've looked at aduinos a little bit, but I know nothing of programming. I agree it does seem like the easiest way.

    Don't know how easy this is to see, (click for the big version) and it's probably not drawn correctly, but this is what I drew up at work the other day. This is using the transformer, rectifier, and regulator that is on the board already.

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