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hi all
I am looking for ideas for the most elegant way to read 3 BCD switches
by elegant i mean less parts, less PIC pins
currently i use the following 7 pin scheme (which works fine):
the 1 2 4 8 pins of the 3 switches are diode combined to 4 PIC pins
the 3 common legs of the switches are driven by 3 more pic pins
if the port does not have pullups you need those too
the part i dislike the most is the high part count of the 12 diodes
ds
Could put all 12 pins of the BCDs on 2 8-bit parallel in/serial out type latches (can't think of a decent part number off the top of my head).
Trigger the load pin to grab the logic levels of all the pins, then shift in the 12 bits manually into a word, split the word up into the individual components and go.
OR...could use a 2nd PIC. Connect the 4 bit outputs of each BCD switch to whatever pins you want on the 2nd PIC. Use a 13th pin on the 2nd PIC as a trigger from the 1st PIC and have the 2nd PIC send out a couple bytes serially to the 1st PIC, which is waiting for it. 2 lines used on the 1st PIC, trigger and serial in. Don't even need to use the serial module, just use SERIN/SERIN2/DEBUGIN/whatever.
Parts count: 1 extra PIC (18 pins, simple firmware), add a 4Mhz resonator (if you use serial, you'd want a real oscillator, not the internal one for accuracy), pullups for the BCD switch lines (which you probably already have). That should be about it.
Hi D.
You might try something like Tip#5 or #7 in this from microchip.
Tips ‘n Tricks
http://ww1.microchip.com/downloads/e...Doc/40040b.pdf
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1 I/O expander such as MCP23016 + 3 resistors should do.
Tons of way to multiplex stuff on low pin count PIC, and then.. this bring this ol', but still good Microchip app note AN234.
http://ww1.microchip.com/downloads/e...tes/00234a.pdf
and
http://techtrain.microchip.com/maste...ses/40040b.pdf
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OK Darrel ;)
ADC is one of my favorite choice...
thanks all
i like the single pin ADC approach, seems like the least stuff
i am already doing pushbuttons this way
too bad there are no res values in the MC app note #7, guess that would spoil the fun
but on 3 bcd sws there would be 1000 combinations, strikes me as too touchy for a 10 bit AD, or am i missing something ?
ds
But I'm sure you only need 512 of them. :)Quote:
Originally Posted by dsicon
Yeah, I think reading all 3 BCD switches on 1 A/D might be a stretch.
But with each digit on different pins, 3 pins would be better than 7.
Then there's only 16 voltage possibilities per pin (10 used). Piece of cake for A/D.
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ds,
Do your switch readings need to be checked often, rearly, only once ?
don
amgen
they will either be polled at the top of the main loop or in response to a button push, haven't started the program yetQuote:
Originally Posted by amgen
it looks like i will be using the 7 pin diode matrix approach after all since it seems to offer the best set of tradeoffs given other considerations in the design, i just really don't like stuffing the 12 diodes due to insertion cost
oh well