Project bikecomputer: multiple 7 segment displays

PlaneTeeR · 2006-01-26 09:31

hello,

I'm starting a project on my school called bikecomputer.
Here I have to develope a computer to show te speed and show the distance and so on..
I'm building it on a board of eduction·with a javalin stamp.

For this project i'm displaying the speed and distance on 7 segment displays (minimum of 3)!

The board had 15 I/O ports, how can i connect those 3, 7 segment displays and use them?

Sorry voor my bad english

Thanks Johnny
Holland

John Astralidis · 2006-01-26 14:32

Hi !

I've started a thread in "Basic Stamp" forum titled: "Adding a speedometer in my BoeBot". Guys that replied gave me an idea of what is possible to do. Check it out, if you can find anything that could help you, too.

Cu.

John.

Paul Baker · 2006-01-26 16:18

This Stampworks exercise should help you to figure out how to·drive multiplexed 7 segement LEDs: http://www.parallax.com/dl/docs/books/sw/exp/sw10.pdf

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
·1+1=10

PlaneTeeR · 2006-01-26 16:43

I've seen that, yes it helped me a little bit further.
I've now connected 2 7 segment displays on my board for testing.
But when i read that code thats been made i don't understand how the do it.
I've got the technical part but don't understand te software part.

thanks

Johnny
Holland

Paul Baker · 2006-01-26 17:10

I can help explain the gist of the software after my two phone interviews scheduled today (after about 4PM (GMT -5)).

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
·1+1=10

PlaneTeeR · 2006-01-26 18:27

Thanks, but i think i'm going with a bcd to control multiple LED.

Johnny
Holland

Paul Baker · 2006-01-26 18:29

BCD is only a method of encoding decimals in binary, it doesn't help you in how to drive the segments, a little patience (in 2 1/2 hours), and Ill strip out all the clock portions of the example and show you the bare essentials of being able to drive the segments with any arbitrary number (which will likely be in BCD).

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
·1+1=10

Paul Baker · 2006-01-26 21:08

Ok the interviews concluded earlier than expected,

 
 
' {$STAMP BS2}

 
' ------------------------------------------------------------------------------
' Program Description:

' This program displays a a 4 digit number on a 4 7 segment LED display
 
' ------------------------------------------------------------------------------
' I/O Definitions
' ------------------------------------------------------------------------------
Segs   VAR OutL ' segments
DigSel VAR OutC ' digit select

 
' ------------------------------------------------------------------------------
' Constants
' ------------------------------------------------------------------------------
DecPoint CON %10000000 ' decimal point bit
Blank    CON %00000000 ' all segments off

Dig0     CON %1111 ' digit select control
Dig1     CON %1110
Dig2     CON %1101
Dig3     CON %1011
Dig4     CON %0111
 
' ------------------------------------------------------------------------------
' Variables
' ------------------------------------------------------------------------------
value VAR Nib(4) ' value to be displayed
digit VAR Nib    ' current display digit

' ------------------------------------------------------------------------------
' EEPROM Data
' ------------------------------------------------------------------------------
' .abcdefg
' --------
DecDig DATA %01111110 ' 0
       DATA %00110000 ' 1
       DATA %01101101 ' 2
       DATA %01111001 ' 3
       DATA %00110011 ' 4
       DATA %01011011 ' 5
       DATA %01011111 ' 6
       DATA %01110000 ' 7
       DATA %01111111 ' 8
       DATA %01111011 ' 9

' ------------------------------------------------------------------------------
' Initialization
' ------------------------------------------------------------------------------
Initialize:
   DirL = %11111111 ' make segments outputs
   DirC = %1111 ' make digit selects outputs
   DigSel = Dig0 ' all digits off

' ------------------------------------------------------------------------------
' Program Code
' ------------------------------------------------------------------------------
Main:
   GOSUB Show_Time ' show current digit


   ' additional code could go here
   GOTO Main 'do it again
END
 
' ------------------------------------------------------------------------------
' Subroutines
' ------------------------------------------------------------------------------
Show_Digit:

   Segs = Blank ' clear display
   ' enable digit
   LOOKUP digit, [noparse][[/noparse]Dig1, Dig2, Dig3, Dig4], digSel
   READ (DecDig + value(digit)), Segs ' put segment pattern in digit
   PAUSE 1 ' show it
   digit = (digit + 1) // 4 ' get next digit
RETURN

Ok this code should work for any 4 digit value stored in the array "value". DecDig is the illumination pattern for each of the digits 0-9. Each time the Show_Digit subroutine is called, it displays the next digit on the next LED. The first line resets the segments (turns them all off), the LOOKUP command activates the next segment for displaying it's digit, the READ command looks up the illumination pattern for the new digit by fetching the value at the base address of the illumination map plus the value of the digit to be displayed and updates the value output to the segment, finally the digit is incremeted with wrap around for the next time Show_Digit is called.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
·1+1=10

Jon Williams · 2006-01-26 21:14

Sorry I didn't catch this discussion earlier -- you can get the explanation for that code from StampWorks 2.0 (though Paul did a great job, as always):

http://www.parallax.com/detail.asp?product_id=27220

You will note that I explain this is simply to demonstrate multiplexing only, and that it's really not appropriate to integrate into programs that require a lot of other work going on.· I think you'll get very poor display results from this once you start trying to read the bicycle's speed.· But... there is a chapter later in the book that shows how to interface to the MC14489 (costs a few dollars) and let you display what you want without having to do the multiplexing yourself.· I also wrote about this chip in Nuts & Volts:

http://www.parallax.com/dl/docs/cols/nv/vol6/col/nv127.pdf

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Jon Williams
Applications Engineer, Parallax

Paul Baker · 2006-01-26 21:33

Thanks Jon, I forgot to mention that the code only suitably works for very light coding in the "' additional code could go here" section. For heavy coding you should use an additional chip to do the LED segment driving grunt work for you like the one Jon suggests.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
·1+1=10

Lejgeo · 2006-01-27 03:45

why not use a cd display instead, thats what they use on pro speedometers...

PlaneTeeR · 2006-01-30 16:05

Jon Williams·said...

Sorry I didn't catch this discussion earlier -- you can get the explanation for that code from StampWorks 2.0 (though Paul did a great job, as always):

http://www.parallax.com/detail.asp?product_id=27220

You will note that I explain this is simply to demonstrate multiplexing only, and that it's really not appropriate to integrate into programs that require a lot of other work going on.· I think you'll get very poor display results from this once you start trying to read the bicycle's speed.· But... there is a chapter later in the book that shows how to interface to the MC14489 (costs a few dollars) and let you display what you want without having to do the multiplexing yourself.· I also wrote about this chip in Nuts & Volts:

http://www.parallax.com/dl/docs/cols/nv/vol6/col/nv127.pdf

Hey Jon,

Sorry for my late reaction.

As I mentioned before, I'm working with the Javalin stamp. Will this chip do better or is it still to slow to get good results with multiplexing? I don't think so myself, so i'm going to find a source for that motorola chip. Thanks for the advise, and hopefully i can figure it out in Java :P.

Johnny Kuiper
Holland

Jon Williams · 2006-01-30 16:25

Well, there is no multiplexer VP in the Javelin so I think using the MC14489 would still be a benefit; that will let your Javelin program focus on the sensor input and measurement calculations.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Jon Williams
Applications Engineer, Parallax

PlaneTeeR · 2006-01-30 17:22

Oke thanks for the advise again. Can I take your recommendation into my rapport?

offtopic:
Will there be more javalin example's in the future?

Johnny Kuiper
Holland

Jon Williams · 2006-01-30 17:37

I don't know the future of the Javelin -- it's not a big seller right now, seems pretty stable, and we don't get many requests for changes. We work like any other company: when we get a lot of requests for something new/updated, we respond.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Jon Williams
Applications Engineer, Parallax

PlaneTeeR · 2006-01-30 17:50

Ah Oke,

Well our school went from Basic to Javalin, because we also have intensive Java programming.
We will see what the future brings...

When I finish this project, I will send it to you...

Johnny Kuiper
Holland

Project bikecomputer: multiple 7 segment displays

Comments