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Groups > comp.arch.embedded > #29155
| From | David Brown <david.brown@hesbynett.no> |
|---|---|
| Newsgroups | comp.arch.embedded |
| Subject | Re: Poor man's PWM |
| Date | 2020-01-29 13:21 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <r0rtch$stl$1@dont-email.me> (permalink) |
| References | <r0o0mu$c6l$1@dont-email.me> <h9as3cFsikkU1@mid.dfncis.de> <r0qvlf$crv$1@dont-email.me> <0b3e27d7-cefc-4821-8df3-62cb140ba68c@googlegroups.com> |
On 29/01/2020 06:54, Rick C wrote: > On Tuesday, January 28, 2020 at 10:54:26 PM UTC-5, Don Y wrote: >> Hi Hans-Bernhard, >> > Yep, clearly a job for an LED driver. > > >>> Overall, hardware that can implement this scheme will thus hardly >>> be any cheaper than hardware that can implement the usual one. >> >> Really? How much for 20 PWM channels? 200? 2000? (I have a 2000 >> LED "moving message" sign at my feet, here -- wanna bet it DOESN'T >> have 2000 PWM channels? Or, 2000 programmable current sources?) > > If you get to 2000 or even 200 PWM channels it should be an FPGA chip > doing all the timing in excruciating detail, any way you would like. > No point in using messy sequential software and always having to deal > with the hassles of interrupt problems. > The way I have seen big LED signs done is with chains of LED driver chips. Each chip supports 8 to 24 chains of LEDs, with each chain having multiple LEDs in series, with support for colour matching as needed. And they all work like big serial-in parallel-out shift registers. As far as the controlling processor is concerned, it's just an SPI device with 2000 bytes for your 2000 LEDs - transferred by DMA in a millisecond. If you had a lower power system - say, 20 mA and one LED per output, you could just use normal logic chip serial-in parallel-out chips. It would take a bit more software to handle different brightness levels, and you won't get as fine control of the levels, but it could be made to work nicely enough with DMA, SPI and a timer. FPGAs are great for making lots of PWM channels, but it would not be so easy to route those signals to the LEDs. So you'd want multiple distributed FPGAs with serial links between them. It could be done, but I'd expect it to be more development effort.
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Poor man's PWM Don Y <blockedofcourse@foo.invalid> - 2020-01-27 17:53 -0700
Re: Poor man's PWM Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-27 19:29 -0800
Re: Poor man's PWM Don Y <blockedofcourse@foo.invalid> - 2020-01-28 20:11 -0700
Re: Poor man's PWM Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-28 20:11 -0800
Re: Poor man's PWM David Brown <david.brown@hesbynett.no> - 2020-01-28 11:29 +0100
Re: Poor man's PWM Don Y <blockedofcourse@foo.invalid> - 2020-01-28 20:34 -0700
Re: Poor man's PWM Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-28 20:32 -0800
Re: Poor man's PWM David Brown <david.brown@hesbynett.no> - 2020-01-29 12:53 +0100
Re: Poor man's PWM Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2020-01-28 14:43 +0100
Re: Poor man's PWM Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-28 12:03 -0800
Re: Poor man's PWM Don Y <blockedofcourse@foo.invalid> - 2020-01-28 20:54 -0700
Re: Poor man's PWM Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-28 21:54 -0800
Re: Poor man's PWM Don Y <blockedofcourse@foo.invalid> - 2020-01-29 00:17 -0700
Re: Poor man's PWM Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-28 23:40 -0800
Re: Poor man's PWM Don Y <blockedofcourse@foo.invalid> - 2020-01-29 00:54 -0700
Re: Poor man's PWM Paul Rubin <no.email@nospam.invalid> - 2020-01-29 00:04 -0800
Re: Poor man's PWM Don Y <blockedofcourse@foo.invalid> - 2020-01-29 02:17 -0700
Re: Poor man's PWM David Brown <david.brown@hesbynett.no> - 2020-01-29 13:21 +0100
Re: Poor man's PWM Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-29 09:51 -0800
Re: Poor man's PWM Paul Rubin <no.email@nospam.invalid> - 2020-01-29 10:07 -0800
Re: Poor man's PWM Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-29 10:14 -0800
Re: Poor man's PWM Paul Rubin <no.email@nospam.invalid> - 2020-01-29 10:28 -0800
Re: Poor man's PWM Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-29 11:40 -0800
Re: Poor man's PWM David Brown <david.brown@hesbynett.no> - 2020-01-30 10:25 +0100
Re: Poor man's PWM Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-30 08:06 -0800
Re: Poor man's PWM David Brown <david.brown@hesbynett.no> - 2020-01-30 21:21 +0100
Re: Poor man's PWM Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-30 15:08 -0800
Re: Poor man's PWM David Brown <david.brown@hesbynett.no> - 2020-01-31 01:17 +0100
Re: Poor man's PWM Rick C <gnuarm.deletethisbit@gmail.com> - 2020-01-30 17:21 -0800
Re: Poor man's PWM David Brown <david.brown@hesbynett.no> - 2020-01-31 10:59 +0100
Re: Poor man's PWM Rick C <gnuarm.deletethisbit@gmail.com> - 2020-02-01 10:18 -0800
Re: Poor man's PWM David Brown <david.brown@hesbynett.no> - 2020-01-30 10:20 +0100
Re: Poor man's PWM Tom Gardner <spamjunk@blueyonder.co.uk> - 2020-01-30 10:13 +0000
Re: Poor man's PWM Paul Rubin <no.email@nospam.invalid> - 2020-01-29 09:57 -0800
Re: Poor man's PWM David Brown <david.brown@hesbynett.no> - 2020-01-30 10:29 +0100
Re: Poor man's PWM Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2020-01-29 16:34 +0100
Re: Poor man's PWM Dimiter_Popoff <dp@tgi-sci.com> - 2020-01-28 17:39 +0200
Re: Poor man's PWM Don Y <blockedofcourse@foo.invalid> - 2020-01-28 19:58 -0700
Re: Poor man's PWM Dimiter_Popoff <dp@tgi-sci.com> - 2020-01-29 18:54 +0200
Re: Poor man's PWM Don Y <blockedofcourse@foo.invalid> - 2020-01-29 00:17 -0700
Re: Poor man's PWM David Brown <david.brown@hesbynett.no> - 2020-01-29 13:39 +0100
Re: Poor man's PWM Paul Rubin <no.email@nospam.invalid> - 2020-01-29 10:08 -0800
Re: Poor man's PWM Don Y <blockedofcourse@foo.invalid> - 2020-04-27 20:13 -0700
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