PWM with PIC16F88 controlling h-bridge

[deimantas]

Hello everyone. I am new one here so don't be hard on me

Ok, let's start with main problem, i have h-bridge and its controlled by pwm. Here is circuit:


My program is here:

' RB0 and RB1 are for PWM
' RB2 is for SD

ANSEL = %00000000 ' All pins changed from analogue to digital
OSCCON = $60 ' Internal clock setted to 4Mhz
TRISB = %00000000 ' All PORTB pins are outputs.
HIGH PORTB.2 ' Turn on sd pin to shutdown ir2110

start:
Pause 100 ' Delay for 100ms waiting for mosfets to settle
low PORTB.2 ' Turned off sd pin
Pause 100 ' delay 100ms
PWM PORTB.0,242,255 ' Pulse sent to PORTB.0 at a duty 'value of 242(95% duty cycle) for 255 cycles.
PWM PORTB.1,012,255 ' Pulse sent to PORTB.0 at a duty 'value of 12(5% duty cycle) for 255 cycles.
PAUSE 100
PWM PORTB.0,127,255 ' 50%
PWM PORTB.1,127,255 ' 50%
PAUSE 100
PWM PORTB.0,012,255 ' 5%
PWM PORTB.1,242,255 ' 95%
PAUSE 100
PWM PORTB.0,127,255 '50%
PWM PORTB.1,127,255 '50%
PAUSE 100
GOTO start
END

I am quite new with picbasic either, so if enyone could help me i would be very grateful.

[deimantas]

One man in other forum told me to try this one, but still nothing :/ maybe here someone will have a clue.

MSpause var byte          ' Milliseconds between charging caps, suggest 10 to 50, even numbers 
Ctr     var byte	  ' Used in loop for 50% pwm
RunCt   var byte	  ' Used in loop
Left   var PORTB.0        ' Don't know which is which, so declare one as left.
Right  var PORTB.1        ' By default, the other is right.
SD     var PORTB.2        ' Shutdown; low=run, high=off.

ANSEL = %00000000 ' All pins changed from analogue to digital
OSCCON = $60 ' Internal clock setted to 4Mhz
TRISB = %00000000 ' All PORTB pins are outputs. 

High SD                 ' Shut down MOSFET drivers
MSpause = 50		' initialize MSPause; 50mS, this will result in about 5 seconds forwards, 
                        '   5 seconds stopped, 5 seconds reverse, 2 seconds stopped.

Loop:
       ' Start the motor turning left.  Full speed ahead!
  
        High Left	 ' Start running left...
        Low  Right       ' Set them opposite
	For RunCt = 1 to 100 ' We're going to loop 100 times, so run time will be MSpause * RunCt
           Low SD           ' Turn on MOSFET drivers
           Pause (MSpause-1) ' wait a bit...
           High SD          ' Turn off MOSFET drivers
           Pause 1          ' Charge MOSFET caps
        Next RunCt

       ' Stop the motor by giving it 50% PWM on both sides.

	For RunCt = 1 to 100 ' We're going to loop 100 times, so run time will be MSpause * RunCt
           For Ctr = 1 to (MSpause >> 1)-2  '  
              Low Right
              High Left        ' Swap direction
              Low SD           ' Turn on MOSFET drivers
              Pause 1
              High SD          ' Turn off MOSFET drivers
              High Right       ' Swap direction
              Low Left
              Low SD           ' Turn on MOSFET drivers
              Pause 1
              High SD          ' Turn off MOSFET drivers
           next Ctr
        Next RunCt

        ' Run the motor in reverse

        High Right
        Low Left
        For RunCt = 1 to 100 ' We're going to loop 100 times, so run time will be MSpause * RunCt
           For Ctr = 1 to (MSpause >> 1)-2  '  
              Low SD           ' Turn on MOSFET drivers
              Pause MSpause    ' delay for a bit
              High SD          ' Turn off MOSFET drivers
              Pause 1
           next Ctr
        next RunCt

	' Driver is shut down, let's just pause for 2 seconds
        Pause 1000
        Pause 1000

        goto Loop      ' do forever
END

But as i read this code and i dont get it why it dont work ;/ it looks everything logically. I meassured pins wile working, and it works good i think, RB0 - 5V after some time it drops to 2.5V and when to zero and RB1 opposite. But RB2 got only 0.12V all time.

[HenrikOlsson]

Hi,
That schematic looks a bit strange to me.....

First, there doesn't seem to be any low side supply voltage (Vcc) as pin 3 seems to not be connected to anything except the bootstrap capacitor and diode. Only the logic supply (Vdd) seems to actually be connected to any supply rail.

Second, even if pin 3(Vcc) and 9(Vdd) ARE connected they are both connected to +5V while the datasheet for the IR2110 calls for a Vcc of 10-20V. The undervoltage protection for the low the side supply (Vcc) kicks in at around 8V which means the bridge drivers aren't even operating.

/Henrik.

[LinkMTech]

HIGH PORTB.2 ' Turn on sd pin to shutdown ir2110

But RB2 got only 0.12V all time.

This pin is made HIGH before the main loop then made LOW within the loop but never serviced again if you are wanting to Shut Down again sometime. That's why it's always LOW.

[deimantas]

Hi,
That schematic looks a bit strange to me.....

First, there doesn't seem to be any low side supply voltage (Vcc) as pin 3 seems to not be connected to anything except the bootstrap capacitor and diode. Only the logic supply (Vdd) seems to actually be connected to any supply rail.

Second, even if pin 3(Vcc) and 9(Vdd) ARE connected they are both connected to +5V while the datasheet for the IR2110 calls for a Vcc of 10-20V. The undervoltage protection for the low the side supply (Vcc) kicks in at around 8V which means the bridge drivers aren't even operating.

/Henrik.

So if i understand correctly i need pin3 connect to 12V supply, y ? Sorry my mistake, its everything okay, just i didn't draw that... pin 3 is connected to 12V supply.

This pin is made HIGH before the main loop then made LOW within the loop but never serviced again if you are wanting to Shut Down again sometime. That's why it's always LOW.

The main point of getting SD low is to make sure that MOSFETS are off at the start. In the loop he used Low sd / high SD for modulating signal and i think i should see that different in tester, or its making turn off/on SD to fast to get that information ? (Sorry for pure language).

[deimantas]

Anyone ? sorry for my impatience, but i have reason for it i need to get this thing work as soon as possible, because it's for my graduation and it slows me from doing other parts.

[HenrikOlsson]

Hi,
Have you disconnected the hardware from the PIC and verified with a scope or whatever that what you think is a software bug really is a software bug and not a problem with your hardware.

If PortB.2 doesn't go high then try something simple, connect a LED to it and do something like:

TRISB.2 = 0    'PortB.2 as output

Main:
 PortB.2 = 1
 Pause 100
 PortB.2 = 0
 Pause 100
Goto Main

Now, does it toggle? If not, double check the ADC and comparator settings in case you have some other functions multiplexed on PortB.2 (I haven't checked). If it still doesn't work, try another pin, perhaps you've fried PortB.2....

Then, when you have that going, move on to the PWM part and get that going - THEN when you know that the software is doing what you think you want (which usually isn't what you really need....), go on and connect the bridge.

/Henrik.

[deimantas]

Hi,
Have you disconnected the hardware from the PIC and verified with a scope or whatever that what you think is a software bug really is a software bug and not a problem with your hardware.

If PortB.2 doesn't go high then try something simple, connect a LED to it and do something like:

TRISB.2 = 0    'PortB.2 as output

Main:
 PortB.2 = 1
 Pause 100
 PortB.2 = 0
 Pause 100
Goto Main

Now, does it toggle? If not, double check the ADC and comparator settings in case you have some other functions multiplexed on PortB.2 (I haven't checked). If it still doesn't work, try another pin, perhaps you've fried PortB.2....

Then, when you have that going, move on to the PWM part and get that going - THEN when you know that the software is doing what you think you want (which usually isn't what you really need....), go on and connect the bridge.

/Henrik.

Yeah thank you for advice. Led's are blinking as i want. But i don't get it why my h-bridge show nosenses, everything is okay but one thing, all 4 drains are high, don't get it why.

[GoldStar]

I always thought the output of 7805 needed a capacitor as well? Anyway I would repace the IR2110 with something easier to use like UCC27322.

You are using just a regular motor right? Not a stepper motor? An oscilloscope will be a great tool to have here to see the pulses at each output.

To be honest, it's easier for me to look at a schematic, try to understand what is going on and then rebuild it as to how I understood it. Takes a little longer but I learn a lot more by thinking about it rather than just putting stuff together and hoping it works.