[chbot] PWM control of William's LED display

[Nathan Kennedy]

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


_______________________________________________
Chchrobotics mailing list Chchrobotics at lists.linuxnut.co.nz
http://lists.ourshack.com/mailman/listinfo/chchrobotics
Mail Archives: http://lists.ourshack.com/pipermail/chchrobotics/
Web site: http://kiwibots.org
Meetings 3rd Monday of each month 6.30pm Science Alive Seminar Room

When replying, please edit your Subject line to reflect new content.