Project idea: Build a scoreboard that counts up to 15. The first component to reach 15 will win! In the event that there is a tie the A=B led will lite, if so play another round.
Today's blog is about the 74ls85 TTL. To build a circuit with this chip you will need two 4 pack dip switches and three leds. A datasheet is below. This TTL will compare the combined value for the 4-bit input of A inputs vs the B 4-bit inputs. The output will send a high to only one of the leds, A<B, A=B, or A>B depending on the condition. Comparison of words greater than 4-bit can be accomplished by cascading 'ls85 as described in the data sheet.
The 74ls85 compares two separate 4-bit words, or numbers, coming from two different sources, such as counter, shift register, etc., including hard-wiring one number on the chip.
One 4-bit word is placed on the inputs A0 thru A3, with the Least Significant Bit on A0.
The other word is placed on inputs B0 thru B3
A 7 segment display can be implemented in the circuit by joining the inputs to a decoder that leads to the display. This will show numeric values..
Larsha Johnson Electrical Engineering undergraduate at the University of South Florida. She enjoys designing electronic circuits (KiCad & NI Multisim), blogging, and creating Youtube tutorials. Newest hobby: Insanely complex PCB outlines.