Hein (fub) wrote,
Hein
fub

  • Mood:

At long last...

Finally I have gotten the shift register train to work -- after more than ten days of fiddling with it.
I connected the powerlines (both positive voltage and ground) on both ends of the little strip of development board that holds the shift registers and the AND-IC -- if power fluctuations towards the end of the 'train' were the problem, then that should have fixed it. But it didn't.

Then I disconnected all the connections from the third shift register. The shift registers share a common Output Enable, Clock and Strobe lines, all driven from a single pin from the PIC. If I disconnected the Clock and Strobe lines, but left the IC in the socket, the other two shift registers worked as intended!
I reconnected the Strobe line, and still all was well. Then I reconnected the Clock line, and things were defective again.

Apparently the voltages and/or the current on the Clock line was insufficient to drive three shift registers. I do drive that line straight off a pin of the PIC, but that was not a problem in the MACH F display.
So I changed the circuit: the pin from the PIC would drive a transistor, with the collector connected to the positive voltage 'power rail' (which sounds impressive, but it is really just a bunch of wire connections tied to the positive voltage from the wallwart adapter) -- this should ensure a correct voltage and as much current as the ICs want/need.

Alas, that did not work. I have absolutely no idea why.

So, I did what any engineer would have done: I worked around the problem. I still have a few pins left, so I connected one of the pins to the Clock pin of the third shift register. Instead of pulling one pin high or low, I now pull two pins high or low. And it works.

I'm not sure why -- but it works. And after ten days of frustration (sometimes I wonder why I consider this a hobby...), I'm not going to pick any nits regarding the solution.
Tags: electronics project
Subscribe

  • Sinterklaas & rhymes

    On a whim, I had bought chocolate capitals for the two colleagues who are in my project, plus for the key people at the client. I wrote Sinterklaas…

  • BlinkenLEDs -- the final frontier

    This evening, I produced the final version of the firmware for the single-matrix BlinkenLEDs circuit. This one has it all. If you recall, I have two…

  • Another day, another blinkenLEDs mode

    So I had this idea yesterday... if I make a large display with multiple LED matrices on top of eachother, wouldn't it be cool to have a…

  • Post a new comment

    Error

    Anonymous comments are disabled in this journal

    default userpic

    Your reply will be screened

    Your IP address will be recorded 

  • 1 comment