PWM to Frequency

[Tobias]

Currently using a 16F886 with any internal or external OSC setting. I am flexible there. I need to read in a square wave that is 300Hz. Based on the incoming duty cycle I need to output a frequency that varies from 0-1500hz and keeping the duty cycle at 50%. What I am doing is trying to fool an electric motor controller into thinking there is a motor connected to it. The controller outputs a PWM for the speed and uses feedback based on a 1500ppr encoder to control the speed. So I want to make a feedback simulator in essence. On the board I have rigged up a couple flip flops so I can divide the frequency out of the PortC.2 by 2,4,8,16 if needed.

Using the Mister E Pic calculator is looks like if I go the CCP route I am going to have to change pre-scalers and the duty cycle on the fly. Will using HPWM be ok for this? I am going to give that route a go first but looking for some input.

Thanks in advance.

[Charles Linquis]

How you go about this depends a lot on the resolution you need. Do you have some idea of that?

[cncmachineguy]

Also, will the pic be deticated to this or are you going to want/need other things frm it also.

[Tobias]

The PIC is dedicated to doing this alone, nothing else.

As far as resolution, the more the better of course. I just don't know how much I can bullshit the controller until I hook it up.

I am playing around with the PULSIN for the incoming PWM and HPWM for the outgoing signal. It seems to be working pretty good.

Here is the code.

Include "modedefs.bas"    ' Mode definitions for Serout
Yellow          Var     PortC.5
Red             Var     PortC.4
Green           Var     PortC.3
Rate            var     PortC.1
LCD             var     PortB.5 

VoltIn          var     word
Flasher         var     word 
Speed           var     word
Numerator       var     word
Divisor         var     word
Total           var     word

Prefix          con     $FE             ' needed before each command
LcdCls          CON     $51             ' clear LCD (use PAUSE 5 after)
CursorPS        con     $45             'Cursor Position
Backlight       con     $53             ' Backlighting 1-8

TRISC = 0000010
TRISB=000000
TRISB=111111 
Option_Reg.7=0    'Pull-Ups Enabled
ANSELH=0          'PortB Digital
WPUB.0=1
WPUB.1=1
WPUB.2=1
WPUB.3=1
WPUB.4=1
INTCON.7=0
Flasher = 0

define OSC 4
'OSCCON.6=1'0    '250khz
'OSCCON.5=0    '250khz
'OSCCON.4=0'0    '250khzHZ
pause 10

SEROUT2 LCD,84, [Prefix,Backlight,8] 'LCD used for debug purpose
Serout2 LCD, 84, [Prefix,LcdCLS]
pause 10
SEROUT2 LCD,84, [Prefix,CursorPS,0, "RPM Simulator "]
pause 1000
Serout2 LCD, 84, [Prefix,LcdCLS] 

high green
high red
high yellow

Repeat
  GOSUB ON_Off     
  Flasher = Flasher + 1
UNTIL Flasher = 5
Flasher = 0

'245 to 24000 for frequency out in the HPWM  23755 range
'15.3HZ to 1.52kHZ at the 1/16 flip flop output

Start: 
  gosub Get_Pulse
  Gosub Math
Goto Start


Get_Pulse:
  Pulsin Rate,0,Numerator
  pulsin Rate,1,Divisor
  Total=Numerator+Divisor
  
  If Total=0 then 'LED Green when PWM present, red when no PWM
     HIgh Yellow
     Low Red
     High Green
     else
     HIgh Yellow
     High Red
     Low Green
  endif
return

Math:
  SEROUT2 LCD,84, [Prefix,CursorPS,0, dec5 Numerator," ",dec5 Divisor, " ", dec5 Total]  
  Divisor=Divisor/10
  Speed = (240*Divisor)
  SEROUT2 LCD,84, [Prefix,CursorPS,64, dec5 Speed] 
  HPWM 1,127,Speed
Return
'___________________________________________
'-----------Activate/Deactivate Outputs-----
On_Off:
  high REd
  high Green
  high Yellow
  PAUSE 100
  high REd
  low Green
  high Yellow
  PAUSE 100
RETURN