7-segment display with P16F84

Hi all, I am new to PIC's but have been studying electronics for 3 years and work as a technician.

I recently came across this site http://www.melabs.com/resources/articles/ledart.htm
with instruction on how to run 7-segment display, i have built the circuit and programmed the PIC with this code: http://www.melabs.com/resources/samp...p/7segment.pbp
but the numbers run really fast and display 0 runs too fast to read it, I have tried adding a PAUSE 1000 under "mainloop" and just below GOSUB display but it only make the displays flash on and off

I am trying to get them to display a number for atleast 1 second each or atleast make it so i can read digit 0

PS I have tried contacting the site but they never got back to me.

Thanks is advance.
once I get this working and learn a little more I plan on adding push buttons and making it into a stopwatch or either a countdown timer.

Raf

Code:

---

i        Var        Byte
n        Var        Byte
Value        Var        Word


        TRISB = $80                ' Set segment pins to output
        TRISA = $f0                ' Set digit pins to output

mainloop:
        For Value = 0 To 9999
                GoSub display        ' Display the value
        Next Value
       
        GoTo mainloop                ' Do it forever

---

You need to modify this patch to something like this

Code:

---

i        Var        Byte
n        Var        Byte
Value        Var        Word
timedelay      var        word

        TRISB = $80                ' Set segment pins to output
        TRISA = $f0                ' Set digit pins to output

mainloop:
        For Value = 0 To 9999
                for timedelay = 0 to 2000
                GoSub display        ' Display the value
                next
        Next Value
       
        GoTo mainloop                ' Do it forever

---

The value you choose for the timedelay will help you persist a value for as long as you choose.

Jerson

Quote:

---

Originally Posted by spitfire

Hi all, I am new to PIC's but have been studying electronics for 3 years and work as a technician.

I recently came across this site http://www.melabs.com/resources/articles/ledart.htm
with instruction on how to run 7-segment display, i have built the circuit and programmed the PIC with this code: http://www.melabs.com/resources/samp...p/7segment.pbp
but the numbers run really fast and display 0 runs too fast to read it, I have tried adding a PAUSE 1000 under "mainloop" and just below GOSUB display but it only make the displays flash on and off

I am trying to get them to display a number for atleast 1 second each or atleast make it so i can read digit 0

PS I have tried contacting the site but they never got back to me.

Thanks is advance.
once I get this working and learn a little more I plan on adding push buttons and making it into a stopwatch or either a countdown timer.

Raf

---

This is the section of code you should try to alter

Code:

---

display:
        For i = 0 To 3                ' Loop through 4 digits
                n = Value Dig i        ' Get digit to display
                GoSub display1        ' Display the digit
                Pause 1                ' Leave it on 1 millisecond
        Next i                        ' Do next digit
        Return

---

This displays each digit for 1 millisecond. try increasing the length of the pause.

By adding your Pause 1000 in the main loop you are adding a 1 second delay between counting. The LEDs are only lit during the display subroutine so you have 4mS of display and then a second waiting to the next 4mS.

Try a 25mS delay (PAUSE 25) or longer to make the digits more visible but you may then notice a flicker across the digits.

Try adding another counting loop so that you only increment the 0-9999 count once every "x" passes through the main loop.

HTH

Keith

Thank alot guys, I was hardly expecting such promt replys.
I will try your suggestions out now.

I got it working using your method Jerson by setting "for timedelay = 0 to 100", works great.

I was wondering if someone could recomend some books or any other good sources of information for writing code?

Cheers,
Raf

Hi Spitfire,
I have bought several books, and without this forum, I would be using them as table levelers, I do not have one I would recommend. Keep reading this forum and the PBP manual, read the archives . . every post, thats waaay better than any book I've seen. Bruce is writing one though :) and when it is published, I will buy one.
JS

Does anyone know where i can get one of those 3 digit seven segment displays that are designed to be multiplexed. aka has 12 pins instead of well loads more.

quick one.
in the 7 seg display program what does ~dcd mean in the line
digits=~dcd i
thanks

Quote:

---

Originally Posted by hoops2006

quick one.
in the 7 seg display program what does ~dcd mean in the line
digits=~dcd i
thanks

---

~ = NOT
and
DCD = it changes a bit number (0-15) into binary and set that bit to a Logic 1

Basicly it finds out what value digits is (0 to 3, 0 being the first display on the right and so on) and converts that into binary if 0 then to 00, if 1 then to 01, if 2 - 10, if 3 - 11 and instead of applying a logic 1 like DCD is supposed to do it does the opposite because there is ~ infront of it which make it 0

Its basicly applying a Logic 0 to pin RA0 on the PIC,completing the subroutine and then doing the same for pin RA1, RA2 and RA3. These are the pins that turn on and off each digit.
Logic 0 normally means 0 or close to 0 Volts but in this case transisors are being used to supply the current to the display. A transistor is basicly an inverting switch so if you input logic 1 (+5V) you get 0 at the output and the opposite if you apply 0 Volts to the input.

I got a little carried away there and have gone into more detail and answering more than you asked but it might help you understand what the code is doing a bit better. Or atleast I hope so.

Many thanks for your reply spitefire just what i needed. I made a boxing round timer a while back, now im trying to improve it by displaying the time on a 7 seg display. its proving to be tricker than i thought. As im still struggling to get my head round this one as im a newbie to pics your extra info helped alot.

No worries hoops, nice project there. Have you got the hardware side finished yet?

I'm also somewhat of a newbie to PICs but after studying discrete logic and designing a 24 hour clock with cmos 4000 series IC's (made my own 4 digit 7-segment display on veroboard using 58 blue LEDs) I now unterstand abit better.

I'm interested to see how it turns out.

Yes i think i have a fair idea of the hard ware. Pretty much the same set up as the link you gave on the first post. Two microswitches for round selection .With a relay chunked in for the buzzer. But my objective for now is to get minutes and seconds counting down on the display. Once i have that ill start worrying about how to select the times i want ect,

So i have plenty to keep me going. ill keep you posted.

Would a count down timer be as simple as:

for sec=59 to 0
pause 1000
if sec=0
then minutes=minutes-1
gosub display.

the value for display would be (minutes*100)+sec eg if 3mins 59 sec value 359
then just display the value as per the code on the link.

Are u in the raf spitfire?

Hi all friend
there is someone can create this project in proteuse and poste it
and thanks

Hi all friend

I have used this listing for over two years without any problems...
and am happy to share it...
ENJOY!!