Multiplex 7 segments
Is their an object out their already that will enable me to control a 7 segment multiplex display with just software and no external devices, like a virtual display driver.
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Comments
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Chris Savage
Parallax Engineering
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Perhaps the BS2, with all of 26 bytes of RAM, is not the device you should be using. Note a 7-segment chip has quite a few pins -- even if you used an SX chip or something, you'd be using up lots of I/O pins for a relatively trivial use. And no, since the BS2 is a single-tasking processor, and not a very fast one at that (2000 PBasic Instructions per second), the 'refresh rate' on a multiplexed display would be pretty low.
And no, there's probably no pre-built code (your "object", I assume) to achieve this.
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Chris Savage
Parallax Engineering
What section is that in, Mike? I am a self taught datasheet reader, so I may be totally missing something fundamental. (Very likely) Help me out of my confusion! [noparse]:)[/noparse]
I see the absolute max per pin of 40ma, and a total of 300ma for both Vdd and Vss. The seven segment I am using (datasheet link:160-1550-5-ND) reaches almost max brightness at 20ma per segment. So with all 7 segments on, that would be 140ma. That is the worst case because the 4 digits are multiplexed, only one digit is powered at a time. So I think I am ok, and the display has been running for several months.
I am sure you are right, but I would like to understand where I am going wrong.
And a PS to my first post. I am using common anodes and the OBEX 7-seg code is for common-cathode devices. I started with the OBEX version, but mad significant changes to change the node-e-ness. The thread creater did not specify which he was using and it makes a big difference.
But then why does it work. 120ma is way-above the propellers 40ma limit. Now I am even more confused.
However, the 1's light stronger then the 8's indicating that the cathode-pins couldn't sink enough current.
I added a LN2803 for the cathode-pins, and inverted the logic in the driver and voila! it works just great.
The datasheet does only give the maximum total current in or out of the chip (300mA) and the current in or out of any one I/O pin (40mA). It may have been an unofficial comment from Beau or Paul regarding the total current for the I/O pins between Vss/Vdd pins on each side of the package that I remembered or maybe I confounded the Propeller with the SX.