LED bargraph with max7219 based on rpm/speed input

Comments

• kuroneko Posts: 3,623

  2012-01-14 20:40 edited 2012-01-14 20:40

  This may need adjustment depending on when you want the first LED to be on. I assume you are after an increasing LED bar starting at 4000 up to 8000.
  
  (rpm - rpm_min) / (rpm_max - rpm_min) = n / number_of_LEDs
  
  with numbers:
  
  (rpm - 4000) / (8000 - 4000) = n / 40
  
  or
  
  n = (rpm - 4000) / 100
  
  For rpm = 4000 this gives you n = 0 (no LED), rpm = 8000 will result in n = 40 (all LEDs). HTH
• chetw77cruiser Posts: 12

  2012-01-14 20:51 edited 2012-01-14 20:51

  That does help, thank you. I am after the increasing led bar but starting at 0 and work up to what ever the max rpm setting is. Sometime after I get this figured out, I might even try to code this for a moving dot instead of bar, but first things first.
  
  I am not sure how to code that and have it output to the max7219. I forgot to mention that I am using spin and I only have a basic knowledge of programing in general, mainly from 15 years ago using qbasic. I am using this project as a learing experience.
• kuroneko Posts: 3,623

  2012-01-14 20:59 edited 2012-01-14 20:59

  Can't help you with that chip in particular (more of a s/w guy). Have a look at [thread=136470]this thread[/thread]. During the w/e the forum is rather slow going but I'm sure others will chime in sooner or later.
  
  How do you get the RPM into your system? Also, if your min/max values are different simply substitute them in the equation.
• chetw77cruiser Posts: 12

  2012-01-15 21:11 edited 2012-01-15 21:11

  Right now I am using the jm_freq object to get the rpm signal and then converting to a useable figure. Here is my code so far. I will most likely be changing to a different way though, so this is not set in stone.
  

  con
  
  _clkmode = xtal1 + pll16x
  _xinfreq = 5_000_000
  
  
  
    #0, CLS, HOME, #8, BKSP, TAB, LF, CLREOL, CLRDN, CR ' PST formmatting control 
    'cyl4 = 30
    'cyl6 = 20
    'cyl8 = 15
    tachin = 2
  
  var
    long rpm,cylsel,redline   
  obj
  
  fc   : "jm_freqin" 
  term : "jm_txserial"
  
  
  pub main | f
  cylsel := 8
  redline := 4500
  fc.init(tachin) ' freq cntr on p0
  
  term.init(30, 115_200) ' start terminal
  waitcnt(clkfreq/10 + cnt)
  term.tx(CLS)
  
  repeat
    f := fc.freq ' get frequency
    if cylsel := 4
      rpm := (f*30/10)
    if cylsel := 6
      rpm := (f*20/10)
    if cylsel := 8
      rpm := (f*15/10)
    term.str(string(HOME, "revs: "))
    
    'rpm := (f*30/10)
    term.dec(rpm) ' print whole part, 30 constant is for 4-cylinder, four-stroke ICE.
    term.str(string(" rpm", CLREOL))
    if rpm > redline
      term.str(string("WARNING"))
    waitcnt(clkfreq/15 + cnt)
  
• chetw77cruiser Posts: 12

  2012-01-15 21:40 edited 2012-01-15 21:40

  After trying multiple ideas, I think that the max7219 is not the best for what I want to do. Whith that in mond, what about using the MM5451 led controller. Basically a large shift register. Any pointers on using this chip?
• Circuitsoft Posts: 1,166

  2012-01-16 10:46 edited 2012-01-16 10:46

  Looks like the 7219 is also just fine. There are, however, 8 registers to write. So, you would fill your two LONGs with the bit pattern for the bar graph. Then, write "(1 << 8) + bottom byte" then "(2 << 8) + second-to-bottom byte" and so on and so forth.
• chetw77cruiser Posts: 12

  2012-01-16 11:41 edited 2012-01-16 11:41

  I goofed and posted the wrong code segment. Here is the correct one.
  

  con
  
  _clkmode = xtal1 + pll16x
  _xinfreq = 5_000_000
  
  
    #0, CLS, HOME, #8, BKSP, TAB, LF, CLREOL, CLRDN, CR ' PST formmatting control 
    'cyl4 = 30
    'cyl6 = 20
    'cyl8 = 15
    tachin = 2
  
  var
    long rpm,cylsel,redline   
  obj
  
  fc   : "jm_freqin" 
  term : "jm_txserial"
  
  
  pub main | f
  cylsel := 8
  redline := 4500
  fc.init(tachin) ' freq cntr on p0
  
  term.init(30, 115_200) ' start terminal
  waitcnt(clkfreq/10 + cnt)
  term.tx(CLS)
  
  repeat
    f := fc.freq ' get frequency
    if cylsel := 4
      rpm := (f*30/10)
    if cylsel := 6
      rpm := (f*20/10)
    if cylsel := 8
      rpm := (f*15/10)
    term.str(string(HOME, "revs: "))
    
    'rpm := (f*30/10)
    term.dec(rpm) ' print whole part, 30 constant is for 4-cylinder, four-stroke ICE.
    term.str(string(" rpm", CLREOL))
    if rpm > redline
      term.str(string("WARNING"))
    waitcnt(clkfreq/15 + cnt)
  
• Chris Savage Parallax Engineering Posts: 14,406

  2012-01-22 15:47 edited 2012-01-22 15:47

  The MM5451 looks like it would be better suited to this task since you're not using groups segments. In this case you could divide max RPM by number of segments and then shift this many bits into your control variable. If I had one of these handy I could whip up something.