[chbot] PWM control of William's LED display

[Morris]

Anyone wanting to control many LEDs should perhaps check out the TLC5947
- it can control 24 LEDs using PWM (or 8 x 3 LEDs for R G B). Check
datasheets for more info.

http://hackedgadgets.com/2010/11/10/rgb-led-circuit-using-the-tlc5947

Cheers

On Tue, 2010-11-16 at 07:26 +1300, Nathan Kennedy wrote:

> I did a bulk order of 74HC595 a while back when I was building my xmas light
> controllers (unfortunately we're not doing our display this year due to
> quake damage), and I've got a few left over.
> 
> I can do them at $1 each (inc gst) if you (or anyone) is interested.
> 
> Thanks,
> Nathan.
> 
> -----Original Message-----
> From: chchrobotics-bounces at lists.linuxnut.co.nz
> [mailto:chchrobotics-bounces at lists.linuxnut.co.nz] On Behalf Of Mark
> Atherton
> Sent: Tuesday, 16 November 2010 7:01 a.m.
> To: chchrobotics at lists.linuxnut.co.nz
> Subject: [chbot] PWM control of William's LED display
> 
> William,
> 
> I have some thoughts about how you could control the brightness of 
> your LED display unit using PWM.
> 
> Brielfy, an 8 bit shift register (74x595 etc) is loaded with a 
> brightness value (0..255) this is fed into the A side of an 8 bit 
> magnitude comparator (2 x cascaded 74x85 etc.). The B side of the 
> comparator is fed with a continuously running 8 bit binary counter. 
> This counter needs to wrap around at about 100Hz. The ">" output of 
> the cascaded 74x85 then becomes the PWM brightness control signal and 
> feeds the enable signal of each of the LED drivers.
> 
> South Island Components's (how do you pluralize that ?) web site 
> claims to have everything in stock...
> 
> datasheets: 
> http://www.nxp.com/documents/data_sheet/74HC_HCT85_CNV.pdf and 
> http://www.fairchildsemi.com/ds/MM/MM74HC595.pdf
> 
> Anyway, just a thought after too much coffee.
> 
> -Mark
> 
> 
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