Bit Angle Modulation (BAM) in a PIC

[gmglickman]

Ioannis:

You might want to remap the LED's brightness curve to compensate for the non-linearity in perceived brightness.

This are the values I use

data @$0, $00,$00,$01,$01,$01,$01,$02,$02,$02,$03,$03,$03,$04,$04,$04,$04,$05,$05,$05,$06,$06,$06,$07,$07,$07,$08,$08,$08,$09,$09,$0A,$0A
data      $0A,$0B,$0B,$0B,$0C,$0C,$0C,$0D,$0D,$0E,$0E,$0E,$0F,$0F,$10,$10,$10,$11,$11,$12,$12,$13,$13,$13,$14,$14,$15,$15,$16,$16,$16,$17
data      $17,$18,$18,$19,$19,$1A,$1A,$1B,$1B,$1C,$1C,$1D,$1D,$1E,$1E,$1F,$1F,$20,$20,$21,$21,$22,$23,$23,$24,$24,$25,$25,$26,$27,$27,$28
data      $28,$29,$2A,$2A,$2B,$2B,$2C,$2D,$2D,$2E,$2F,$2F,$30,$31,$31,$32,$33,$33,$34,$35,$35,$36,$37,$37,$38,$39,$3A,$3A,$3B,$3C,$3D,$3D
data      $3E,$3F,$40,$40,$41,$42,$43,$44,$44,$45,$46,$47,$48,$49,$49,$4A,$4B,$4C,$4D,$4E,$4F,$50,$51,$51,$52,$53,$54,$55,$56,$57,$58,$59
data      $5A,$5B,$5C,$5D,$5E,$5F,$60,$61,$62,$63,$64,$65,$67,$68,$69,$6A,$6B,$6C,$6D,$6E,$6F,$71,$72,$73,$74,$75,$77,$78,$79,$7A,$7B,$7D
data      $7E,$7F,$81,$82,$83,$84,$86,$87,$89,$8A,$8B,$8D,$8E,$8F,$91,$92,$94,$95,$97,$98,$9A,$9B,$9D,$9E,$A0,$A1,$A3,$A4,$A6,$A7,$A9,$AB
data      $AC,$AE,$B0,$B1,$B3,$B5,$B6,$B8,$BA,$BB,$BD,$BF,$C1,$C3,$C4,$C6,$C8,$CA,$CC,$CE,$D0,$D1,$D3,$D5,$D7,$D9,$DB,$DD,$DF,$E1,$E3,$E6

Then just

READ LED, LED

[Ioannis]

Hi gmglickman,

Hmm, nice, thanks for the post. I was thinking more complicated on this!

Ioannis

[Caius1]

Hi,

I came across this topic when browsing for BAM.

Regarding the blink can you verify that the blink still occurs when:
1 The last value of the period = 2^nBits - 2 instead of 2^nBits-1
2 New value is only updated at the start of a pwm period.

It would seem strange to me if it does.
I think that a blink can only occur form value=0 to value=x

Thanks

[Darrel Taylor]

Regarding the blink can you verify that the blink still occurs when:
1 The last value of the period = 2^nBits - 2 instead of 2^nBits-1
2 New value is only updated at the start of a pwm period.

I assume you mean reversing the order of bits 6 and 7.

Yes, the blink still occurs. It just happens at different numbers.
No matter which way you order the bit's, if they are only scanned in one direction, there will always be a blink at some point.

I also found that at other points in the dutycycle, the original BAM has several more less obvious blinks as the phase shift does the exact same thing in the lower bits. You just can't see them as well because they are shorter periods. But if you stare right at the LED straight on, you can definitely see them.

However, the symmetrical nature of the Mirror Imaged waveform, completely eliminates ALL of the blinking. It's really amazing how well it fixed the problems.

You can see how it works from the animation in this thread ...

MIBAM - (Mirror Imaged Bit Angle Modulation)
http://www.picbasic.co.uk/forum/showthread.php?t=10564

[vtt-info]

Hi Darrel.

I am testing your Cylon Scanner
code on a 887 chip at 8MHz.

I am stuck on this error:

Error[118] c:\pbp\mibam-~1.asm 97:Overwriting previous address contents (2007)

In fact, the code is a copy of the example. Nothing more or less. Of course the part about wsave is included too. Attached is the final test code.

Regards,
Konrad
MIBAM_Cylon.pbp.txt

[Darrel Taylor]

Try this thread ... post#5

Presetting Configuration Fuses (PIC Defines) into your Program
http://www.picbasic.co.uk/forum/showthread.php?t=543

Or, just delete the __config line, which will then use the PBP default configs.
<br>

[lanyong]

u will let it to 2.45kHz. the led will be not blink. i have test it.

last week, i send some thread. they r disappear, my god!

mbam will not solve the blink problem absolutely. from 127 to 128 change so much the same.

the best way is let more interrupt. and let the bit7 or bit6 or bit5 or bit4's time average in the period.

[Bronx68]

Darrel,
I started this link when I was working on an RGB backlight. I have been away from this task for quite some time but plan to get back into next month.
You mentioned that you are willing to let someone test out your code. I am using a 16F819. Will it run on this chip? Are you still looking for someone to do some testing?

[Bill Legge]

DT

I'm sorry to ask a basic question when this development/discussion is well under way.

I don't see why one PWM output needs 256 interrupts per cycle? I would have thought only one was needed - at the appropriate time in the cycle?

I'm missing something here - probably brains!

Regards Bill Legge

[Bill Legge]

DT

Sorry to ask a basic question when the discussion is well advanced.

I don't see why 256 interrupts are needed for one PWM signal? I would have thought that one interrupt - at the appropriate time - in the cycle would do the trick?

I'm missing something? Brains?

Regards Bill Legge