[sdiy] 7-segment LED displays with 4511 driver chip - max current?
rick.jansen at xs4all.nl
Thu Aug 6 07:29:38 CEST 2015
> On 06 Aug 2015, at 00:01, rsdio at audiobanshee.com wrote:
> Those three BCD chips will use 12 GPIO pins, unless you add more chips to expand I/O. With those same 12 GPIO pins, you can drive 36 LEDs in a simple matrix. That's enough for three 7-segment displays plus 15 more LED indicators. Or, you could use 10 GPIO pins and a cheap 2-to-4 decoder chip to drive 32 LEDs with 11 to spare beyond the three 7-segment displays.
The 4511 has a latch that can remember the state of the digit. So you need 4 pins for the BCD value, plus one pin per LE signal to make that 4511 change state. Three 4511's cost 7 pins that way. I do have enough space in the I2C bus, so I will add an extra PCF8574 for that. One bit spare for blanking the upper digit even, if 0! :-)
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