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Seven Segment display

Hello everyone,

I was wondering if I could use a 28 pin IC, and treat 26 pins (except + and -) as i/o to connect 2 seven segment displays using the 4511b to limit the pin usage to 8 and then have 12 free pins for output and one as input for a button.

Can this be done? hope it can :)

Thanks in advance.

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Use CMOS 4026 chips, then you only need 2 output pins (clock and reset) to display any n-digit number with n CMOS 4026 chips, see picaxe manual 3, page 22.

I see i can use the 2 4511b and will the i/o work? because i need to have 12 outputs to control 12 transistors for voltage regulation will i have those 12 pins?, thats what i didnt get.


Well yeah, if you have 26 general I/O pins and you use up 8 of them you'll have 18 left, so plenty for your 12 transistors and 1 button, plus a few spares.

I don't know what your "28 pin IC" is so I can't really confirm that you'll have that many I/O available, if that's what you're asking.

Sorry what I meant was a 28 pin PIC, like the PIC18F2520

For example the Picaxe 28x1-28x2 use a 28 pin but i am not sure if i can have that many i/o as many of the outputs say out c3, c4, etc...


Yep, you'll have plenty of I/O pins.

Yes, you can do this. 4 pins per 7-segment display via a 4511B each is fine if you tie the LE pin to ground, and both BI and LT pins to Vdd.

There are other options that can further reduce the pins required, such as using two 3-8 decoders/demultiplexers (3 pins per display), or using a shift register/port expander (as low as 2 pins for both displays), but these options require more programming work, and more effort by the controller.