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Eric Adamson
- Jan 1, 1970
- 0
I'm developing a multiplexed two-digit hex display using 7-segment displays.
Multiplexing and BCD-hex encoding are being handled by a PIC. Diagram can
(hopefully) be seen at:
http://forum.microchip.com/upfiles/23628/Rp42593.png
My question relates to the inverter which is used to select the digit to be
driven, and how it should be implemented. I'm looking at a 74HC04, but find
that it's current rating is only around 4mA. Apologies for not having the
LED specs handy, but I'm headed off to work -- general advice would be fine.
It appears to be relatively efficient, and given that only one segment will
be driven at any given instant, my current requirements should remain fairly
low, save perhaps any need to overdrive for brightness compensation.
I'm not using the 74HC04 for anything else, so wiring several gates in
parallel seems a reasonable way to increase current capacity. The PIC can
source/sink at least 20mA, so it's probably fine to drive the segment which
appears at the inverter input, but I'm wondering whether it still might be
preferable to lose the inverter IC and buffer the RA? line with discretes.
BTW, the entire post can be accessed at this URL:
http://forum.microchip.com/m.asp?m=42520&mpage=1
Thanks in advance, for any advice you can offer.
Eric Adamson
Lansing, Michigan
Multiplexing and BCD-hex encoding are being handled by a PIC. Diagram can
(hopefully) be seen at:
http://forum.microchip.com/upfiles/23628/Rp42593.png
My question relates to the inverter which is used to select the digit to be
driven, and how it should be implemented. I'm looking at a 74HC04, but find
that it's current rating is only around 4mA. Apologies for not having the
LED specs handy, but I'm headed off to work -- general advice would be fine.
It appears to be relatively efficient, and given that only one segment will
be driven at any given instant, my current requirements should remain fairly
low, save perhaps any need to overdrive for brightness compensation.
I'm not using the 74HC04 for anything else, so wiring several gates in
parallel seems a reasonable way to increase current capacity. The PIC can
source/sink at least 20mA, so it's probably fine to drive the segment which
appears at the inverter input, but I'm wondering whether it still might be
preferable to lose the inverter IC and buffer the RA? line with discretes.
BTW, the entire post can be accessed at this URL:
http://forum.microchip.com/m.asp?m=42520&mpage=1
Thanks in advance, for any advice you can offer.
Eric Adamson
Lansing, Michigan