Designing a 7 seg display driver without using an IC

[BRUCErulz]

I would like to drive a 7 segment display without using an IC.
I would like the display to produce the digits 0 thru 9
I would like to display each digit with a separate SPST switch off/on
Is there a way to do such a thing without having to run 49 seperate lines with
diodes to cover all possibilities?

The display would be several feet from the switch panel. I know I would need a min of 11 lines between them, 10 positive and a common if I used some sort of junction bus at the display but still a rats nest in the end...

Would it be possible to create a logic board using only pnp transistors?
Such as: If a "4" is desired, SPST switch #4 is closed and segments bcfg are powered... If an "8" is desired, SPST switch #8 is closed and segments abcdefg are powered.

BRUCErulz

 

[IanP]

7 seg display driver

It looks like 49 diodes is the simplest circuit one can make - without a 7-segment decoder IC, that is ..

Regards,
IanP

 

[Gorgon]

Re: 7 seg display driver

Use an old EPROM to do the decoding. Yeah, I know it's an IC

TOK

 

[jit_singh_tara]

Re: 7 seg display driver

well i know u not interested in using ic , but still if u plan to use 8051 it will b much much easier.i m sure u must b having well valid reason for not using it.

 

[gdaporta]

Re: 7 seg display driver

You don't want to use a uC and you don't want to use any TTL or CMOS logic ???

If you could use CMOS or TTL, you could use less lines using a BCD to 7 segment driver. In the side you have the 7 segment display, you use this driver, and you receive the bcd code. To transmit the bcd code you only need 4 lines for data.
In the side you have the sw, you have to make a digital development to transmit the bcd code.
In that way you would use a lot of ic's and you have to make the digital development using any of the techniques like k-maps or quine mc clousky (or something like that).

The better way is using a uC. In these days nobody use a digital development to control a 7 segments display.

Why you dont´t want to use a uC?

By,

GuillerMo (AR)

 

[BRUCErulz]

Re: 7 seg display driver

I was staying away from the Ic because I needed to build a scoreboard using LEDs and I needed to build it fast. I did not have an IC to do the job and I thought I could mangage the project just as easily without one. I was wrong. BTW, which came first? The 7 seg dis driver or the 7 seg display?

BRUCE

 

[white_shadow]

Re: 7 seg display driver

I would like to drive a 7 segment display without using an IC.
I would like the display to produce the digits 0 thru 9
I would like to display each digit with a separate SPST switch off/on
Is there a way to do such a thing without having to run 49 seperate lines with
diodes to cover all possibilities?

The display would be several feet from the switch panel. I know I would need a min of 11 lines between them, 10 positive and a common if I used some sort of junction bus at the display but still a rats nest in the end...

Would it be possible to create a logic board using only pnp transistors?
Such as: If a "4" is desired, SPST switch #4 is closed and segments bcfg are powered... If an "8" is desired, SPST switch #8 is closed and segments abcdefg are powered.

BRUCErulz

Let me get this straight. You want to display (1) seven-segment LED to show any number 0-9. You want to do this without using any IC's and will incorporate (SPST mechanical) switches. By activating one of ten switches, a corresponding digit will be displayed. Is this correct?

You're confused (or I read your post wrong) about how to go about this project. I doubt you need 49 lines, 10 switches, or a min of 11 lines between them (whatever that means).

To start, you can display 0-9 with four switches using 8421 code. But for simplicity if you want a"one switch-one number" approach, it will actually make the design a little more complicated. You will need a 10-1 mux.

Added after 7 minutes:

I'm sorry, but I just realized what you wanted to do in your design and that my post may be misleading.

If you want a "one switch-one number" approach, then you simply go from a 1-of-10 code to your abcdefg code.

 

[echo47]

7 seg display driver

You can group common segment combinations to reduce the number of diodes to about 30. However, the segment brightness will vary slightly due to different numbers of diode voltage drops.

How about using one eleven-position rotary switch (OFF and 0-9) instead of ten SPST switches?

 

[nguyennam]

Re: 7 seg display driver

I understand that you are not familiar to the IC, especially logic and microcontrollers.

Using 49 diodes is one of the solution, however, it is so "rough" and when there is a problem, it is hard for you to point out it as it is so complicated.

You need not to use the microcontrollers as you do not want to write codes.

But I believe that if you look through the datasheets of the logic 74LS147 and 74LS47, you can easily understand how to make your circuit in very simple way:

74LS147 is a 10-line to 4-line (decimal to BCD) priority encoder. If all of 9 input set at logic 1, so all output are set at logic 1 which corresponding to number 0.

If any input is set at logic 0, regardless the other inputs at any logic level, so the ouputs are set at the corresponding number.

4-line outputs (BCD) are interpreted in to number (LED 7-segment display) by the 74LS47, it is the BCD to 7-segment decoder/driver.

All inputs of 74LS147 are pulled up to +5V through resistors of any in range of 1kohm to 10kohms, and your 9 switches (normally opened) connect the inputs to ground.

That is all of the idea. As I do not know how to draw the circuit and post on to forum, so I hope all my explanations are clear enough for you.

Goodluck
nguyennam

 

[camel84]

7 seg display driver

you can easly use MAX7219.It's an driver, you can order a sample free in maxim site.. see it.