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7 Segment Display Help

Question asked by syee10 in #Coffee Room on Oct 10, 2010
syee10
syee10 · Oct 10, 2010
Rank E1 - BEGINNER
Hi all,

I am designing a four digit 7 segment display just using IC 74LS90 decade counter and 74LS47 BCD to 7 segment driver. My question is how to link the 74LS90 decade counter together so that the four 7 segment display will show me the result? Posted in: #Coffee Room
shahrul
shahrul · Oct 10, 2010
Rank C3 - EXPERT
I never use this IC, why you not use microcontroller?
cbaber
cbaber · Oct 11, 2010
Rank E1 - BEGINNER
Datasheets are your best friend. Here you go:

https://focus.ti.com/lit/ds/symlink/sn7447a.pdf
74LS90 pdf, 74LS90 description, 74LS90 datasheets, 74LS90 view ::: ALLDATASHEET :::

You should be able to just hook up the outputs from the counter to the inputs of the BCD to 7-segment. Then the outputs from the display driver to the 7-segment display. This is going to be hard without microprocessor control though. I assume you want to do some sort of stopwatch or clock. I did a stopwatch with 4 7-segment leds using a microprocessor and basically it was interrupt driven. A timer interrupt controlled my count, while another interrupt cycled through each 7-segment led, giving the sense that all 4 were on at one time. I created an array of numbers for the digits on the display. Also had button control for stop, start, and reset.
Harshad Italiya
Harshad Italiya · Oct 13, 2010
Rank A1 - PRO
shahrul
I never use this IC, why you not use microcontroller?
It is a very simple design and the output of that IC is direct Binary compatible i think that's why there is no need of controller
cbaber
cbaber · Oct 13, 2010
Rank E1 - BEGINNER
godfather
It is a very simple design and the output of that IC is direct Binary compatible i think that's why there is no need of controller
Yes but he is wanting to use 4 of the 7-seg. leds. All the IC will do is count up, and if you hook it up without a controller it will just display 0-9 over and over on all 4 digits. You will need seperate counter IC's for each digit, and each IC will need a different clock to get the stopwatch effect. In my opinion just use a microcontroller, cut out the counter IC's, and use software to control it all.
jivv
jivv · Oct 16, 2010
Rank E1 - BEGINNER
Hi syee10,

I checked the 74LS90 datasheet and I don't see any Ripple-Carry pin for this chip, so you are going to have to use MR1 and MR2 (pins 2 and 3) to reset the counter when Q0Q1Q2Q3 = 0 1 0 1. At the same time you are going to use that combination as clock for the next counter, that way when the first counter hits 10, the display is going to be re-set to 0 and the next counter will increase the count.

The connection to the BCD to 7 segment decoder is straight forward. You don't need a microprocessor (or microcontroller), you only need a clock (for the first counter) and a 7408 (quad 2-input and) and you'll be all set.

I hope that helps

Cheers

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