Drive 4digit 7Segment by PIC16F84A

[takao21203]

People don't always think of Ohm's law.
If you have yellow LED, these LED will drop 2.0 to 2.2 volts.
If you use 2.4 volts supply (2x rechargeable battery), the PIC voltage drop is only 0.2 to 0.4 volts.

The electric Power is calculated from current, and voltage drop!
So the chip remains cool. The value in the datasheet is the current for full voltage drop across the PIC (I think).
This is maybe the reason why the PIC does not burn from LED.

For individual LED resistors should be used if the LED is too bright.

Here is also schematic + source code + datasheets for LED display drive using serial buffers.
I don't think it's the same display as in your photo.
http://pic.hitechworld.org/716pcb/ (directory only not web page)

[takao21203]

Actually I have built this circuit today:
viewtopic.php?f=21&t=11551

Not because of this thread, but because I am working at display PCBs
on request of a customer.

The 16f884 does not heat up, and as for today, it works.
I will do one or two months testing.
It's not totally professional because there is a little brightness variation.
That also is not always really relevant (if you only want a display for a prototype,
and not a super even brightness or total relieability for many years).

I use 2x 4 digit displays, the segments connected in parallel, and 8-phase multiplex.