BCD to hexadecimal 7 segment LED driver

Once upon a time in the 70's Motorola came out with a BCD to hexadecimal 7 segment LED driver in the MC144xx series,

Instead of displaying rubbish characters between binary input 1010 to 1111 it displayed hexadecimal A to F

But wait that is not all, it did not need 7 limit resistors, that so many (all) other "BCD to 7 segment LED drivers" need,

Every time I see a circuit that uses "BCD to 7 segment LED driver" in it there are also the other 7 resistor there too,

I thought it was great I used a few, I wonder why they never took off

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Hmm. Are you sure you're not conflating the DM9368 driver chip from Fairchild vs. the Motorola MC14511 (which is a CMOS chip with NPN emitter-follower bipolar drivers, and does require current limiting resistors)? That's the only one that I can recall that decoded hex, and it also had the constant current outputs of which you speak.

The reasons probably had to do with second sources, price and availability. That's why we never used them. OTOH, there's a 4511 in each of our mass-produced CO detectors we have at home.

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

MC14495 is I think what you're writing about.

The Fairchild DM9368 is still out there and does hex too.

TI and I think HP also had LED displays with on-display hex decoders/drivers.

There are lots of LED driver chips from TI/Allegro/Micrel which have constant current drivers on the chip. They do not do hexadecimal decoding, their input interface is simply a bit-per-segment shift register, this works great with modern microcontrollers, you simply have a little lookup table in your program to produce the desired display.

A bit older (but I think still available) is the MM5450 for LED driving.

The Motorola MC14499 put a four-digit seven segment multiplexed driver into a single 16-bit DIP, with a serial interface for data in. But it didn't do hex.


Reply to
Tim Shoppa

They were obselete not long after their introduction. After the late '70s, just about everything with a display used a microprocessor.

Jameco probaly still has them. At only two or three times the price of a PIC.

Mark Zenier snipped-for-privacy@eskimo.com Washington State resident

Reply to
Mark Zenier

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