My prof assigned me a bonus project to try out. We current built a basic Binary display using 4 switches and the 7447 convert to light up a seven segment display. The challenge is to build a counter that will take 7 input binary, for 0-99 and display it with two seven segment displays on a digital board. I need to figure out a way to build this using IC chips. Now I'm not looking for the answer in plain English hints would be nice. He suggest using a full adder but when looking at this I cannot seem to find a way to use it. I started to configure a set up but its starting to use way to many chips, and it seems like I am just making inputs for every number from 0-99.
the lowest bit will be easy after that it gets interesting.
one way would be a 128 byte rom :)
I see two possible approaches,
one is massed logic, just figure out how each output bit is determines by the input bits..
the other is synchronised counters, drive two counters one that counts base 10 and drives the display and another that counts in bibary and you compare with the input.
or even better a presettable binary down counter, and a two-digit BCD up counter.
look up these (cmos 4000 family) part numbers. 4553 4516 4518 4029 download the datasheets and see what you can do. eg type "4553 datasheet" in the google search box and see where it takes you.
Sound like your prof is playing a trick on you. (Did you get this assignment on April 1?)
The conventional approach (way back when people actually did these things with discrete chips) is to use decade counters, such as the 7490, which can be cascaded to count as many digits as you like. Each 7490 sends its output to one 7447. No adders needed!
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The brute force way is to load the seven bit binary number into a binary down-counter and at the same time to clear two BCD counters connected in cascade. Then clock them both with the same clock and stop counting when the binary counter gets to zero. The BCD counters will now have as outputs the BCD value of the binary number loaded into the down-counter.
lots of answers from other people here (mostly jokes, right?)... but.. the best way to do it is with 2x 74LS185 - they are designed exactly for this job.
Forget about counters and stuff, these two chips correctly arranged will provide the correct BCD outputs to feed into your 7447s - i.e exactly what you want.
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One thing is not clear to me: Do you have a 7-bits binary counter (so you need to convert from binary to BCD to 7-segment) or do you need a BCD counter that outputs directly in 7-segment? Or even some other scheme?
As for using full adders for conversion, suppose "In" to be the binary input and "Out" to be the BCD output, you get:
You were correct the first time, it only takes 2x to do the numbers 0 - 99 with a 7 bit binary input. Good luck finding a supplier, I could hardly find a datasheet. ;-)
doing it with an eprom is quite easy and, Ithink, the best option.
eproms work by you providing a binary address (i.e. what you are currently providing to you 7447 and giving out a piece of data (8 bits
- just right to feed 2x 7447)
you will need to make sure that whatever eprom you use, you ensure the CS is low and the output (OE or RD) on some is also enabled all the time.
then you need to work out what combination of data patterns comes out... here is a list of the data for each address... assuming you are driving two 7447, the Left most digit driven from the least significant 4 bits (D0 - D3)
all addresses and data are in HEX.
connect your 7 bits of data to A0-A6 and connect all other address lines to 0V
should have this up and running is 2 hours max - assuming you have access to an EPROM programmer
here is a list of the data for each address... assuming you are driving two 7447, the Left most digit driven from the least significant 4 bits (D0 - D3)... Not really my habit to spoon feed, but trust me - this will lead to greater things once your creative juices start flowing.
instead of doubling up your eproms (or using a big beastie) why not just use A7 as a strobe and provide both seven seg data on the single data outputs.
what? a two chip "discrete TTL" solution to do exactly what the OP wants - fail to see the joke. The internal construction of the chip has no bearing...
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