Reply by bitrex June 17, 20162016-06-17
rickman <gnuarm@gmail.com> Wrote in message:
> On 6/16/2016 10:48 AM, bitrex wrote: >> On 06/16/2016 10:38 AM, Peter Heitzer wrote: >>> rickman <gnuarm@gmail.com> wrote: >>>> On 6/15/2016 1:34 PM, bitrex wrote: >>>>> Is there a CMOS-type substitute for the 74LS47 with "open collector" >>>>> type outputs suitable for sinking around 20mA? >>> >>>> There are about a million I2C/SPI LED drivers out there that have built >>>> in PWM dimming. Have you looked at any? >>> I think the OP is looking for a part costing less than a dollar. The >>> drivers I found are rather costly. >>> >>> >> >> Yup. Definitely looks like the cheapest way is to drive the segments of >> the common anode display directly to ground right from a uC, if it can >> take the punishment. >> >> If there were more displays to drive instead of instead of just one, it >> might be worth looking at using a dedicated driver chip for each >> display. Or who knows, it might still be cheaper to use a uC for each >> display, slaved together on a serial bus. > > MCUs often have a total sink rating which can limit how many loads you > drive at the same time. > > Not sure what you've found before, but a quick search turned up some TI > parts, TLC6C598 - 8 bits, $0.34 and TLC6C5912 - 12 bits, $0.50 at 1k > quantity. These are basic shift registers with a clear and buffer > register (open drain output) with a blanking control which can be used > for PWM. 30 mA per output up to 40 volts. Supply current in uA. > > -- > > Rick C >
The TLC6C598 is a cool part...if at some point I have to control more than one display it would make sense to use that for each and drive them from a single uC, I was surprised though that most AVR uCs in SOIC can sink a total of 200 mA to ground, at usually 20 mA or over per pin. The packages have a total dissipation rating of 500 mW at 30C, so if the output low voltages are only a few hundred mV I think I should come in under that, even with 7 segments. -- ----Android NewsGroup Reader---- http://usenet.sinaapp.com/
Reply by WangoTango June 16, 20162016-06-16
In article <%kg8z.2$e94.1@fx01.iad>, bitrex@de.lete.earthlink.net 
says...
> Is there a CMOS-type substitute for the 74LS47 with "open collector" > type outputs suitable for sinking around 20mA? > > That uses less quiescent power than the 47's ~10mA. Supply voltage > either 5 or 3.3 volts, depending. It doesn't really matter if the chip > itself does a conversion from BCD to the appropriate outputs, as that > mapping can be done in software, but the chip would need to have at > least a 3 bit address space. > > The '47 has an input that's suitable for dynamic dimming of the loads by > applying PWM, it would be cool if the replacement had something like that. > > I think JL posted something along these lines in response to another > question of mine, but I can't find the thread. >
I had to update a product that used two of them recently. What I opted to use was an AS1109. It uses an SPI style interface instead of a parallel BCD input and you will need to use a look up table for the decoding, but that's all pretty trivial. It has a single input for dimming and you can daisy chain them together so you don't need multiple /CS lines. It also has the advantage of a built in CC driver, so you don't need to put down individual resistors for each output and a dimming input that handles all the output channels. Don't know if that will work for you, but it's worth a look. http://www.digikey.com/product-search/en?mpart=AS1109-BSOT&v=961
Reply by rickman June 16, 20162016-06-16
On 6/16/2016 10:48 AM, bitrex wrote:
> On 06/16/2016 10:38 AM, Peter Heitzer wrote: >> rickman <gnuarm@gmail.com> wrote: >>> On 6/15/2016 1:34 PM, bitrex wrote: >>>> Is there a CMOS-type substitute for the 74LS47 with "open collector" >>>> type outputs suitable for sinking around 20mA? >> >>> There are about a million I2C/SPI LED drivers out there that have built >>> in PWM dimming. Have you looked at any? >> I think the OP is looking for a part costing less than a dollar. The >> drivers I found are rather costly. >> >> > > Yup. Definitely looks like the cheapest way is to drive the segments of > the common anode display directly to ground right from a uC, if it can > take the punishment. > > If there were more displays to drive instead of instead of just one, it > might be worth looking at using a dedicated driver chip for each > display. Or who knows, it might still be cheaper to use a uC for each > display, slaved together on a serial bus.
MCUs often have a total sink rating which can limit how many loads you drive at the same time. Not sure what you've found before, but a quick search turned up some TI parts, TLC6C598 - 8 bits, $0.34 and TLC6C5912 - 12 bits, $0.50 at 1k quantity. These are basic shift registers with a clear and buffer register (open drain output) with a blanking control which can be used for PWM. 30 mA per output up to 40 volts. Supply current in uA. -- Rick C
Reply by bitrex June 16, 20162016-06-16
On 06/16/2016 10:38 AM, Peter Heitzer wrote:
> rickman <gnuarm@gmail.com> wrote: >> On 6/15/2016 1:34 PM, bitrex wrote: >>> Is there a CMOS-type substitute for the 74LS47 with "open collector" >>> type outputs suitable for sinking around 20mA? > >> There are about a million I2C/SPI LED drivers out there that have built >> in PWM dimming. Have you looked at any? > I think the OP is looking for a part costing less than a dollar. The > drivers I found are rather costly. > >
Yup. Definitely looks like the cheapest way is to drive the segments of the common anode display directly to ground right from a uC, if it can take the punishment. If there were more displays to drive instead of instead of just one, it might be worth looking at using a dedicated driver chip for each display. Or who knows, it might still be cheaper to use a uC for each display, slaved together on a serial bus.
Reply by Peter Heitzer June 16, 20162016-06-16
rickman <gnuarm@gmail.com> wrote:
>On 6/15/2016 1:34 PM, bitrex wrote: >> Is there a CMOS-type substitute for the 74LS47 with "open collector" >> type outputs suitable for sinking around 20mA?
>There are about a million I2C/SPI LED drivers out there that have built >in PWM dimming. Have you looked at any?
I think the OP is looking for a part costing less than a dollar. The drivers I found are rather costly. -- Dipl.-Inform(FH) Peter Heitzer, peter.heitzer@rz.uni-regensburg.de
Reply by bitrex June 16, 20162016-06-16
On 06/16/2016 07:11 AM, Peter Heitzer wrote:
> bitrex <bitrex@de.lete.earthlink.net> wrote: > >> Looks like setting it up for the Tiny84 is straightforward these days: > >> http://highlowtech.org/?p=1695 > >> The Tiny84 only has 12 pins, but even that is more than I need. I'd >> prefer the larger code space, 8k vs 2k for the 2313. They're both about >> the same price in quantity at Mouser. > That makes sense. If you program the uC in C 2 KiB can be used up > easyly if you happen to use "printf" or its friends. You also could > use linear code more easyly if you need speed for some tasks. >
I have a slight pathology in that I like using C++, even for "small" projects. avr-g++ compiles pretty efficient code, so long as one avoids using a ton of "virtual" methods, and initializes all memory required for the system at startup and then doesn't use the "new" operator to do anything but place or copy objects onto pre-allocated memory. I think the moderate increase in code size is worth the advantages gained in portability/maintainability.
Reply by rickman June 16, 20162016-06-16
On 6/15/2016 1:34 PM, bitrex wrote:
> Is there a CMOS-type substitute for the 74LS47 with "open collector" > type outputs suitable for sinking around 20mA? > > That uses less quiescent power than the 47's ~10mA. Supply voltage > either 5 or 3.3 volts, depending. It doesn't really matter if the chip > itself does a conversion from BCD to the appropriate outputs, as that > mapping can be done in software, but the chip would need to have at > least a 3 bit address space. > > The '47 has an input that's suitable for dynamic dimming of the loads by > applying PWM, it would be cool if the replacement had something like that. > > I think JL posted something along these lines in response to another > question of mine, but I can't find the thread.
There are about a million I2C/SPI LED drivers out there that have built in PWM dimming. Have you looked at any? -- Rick C
Reply by Peter Heitzer June 16, 20162016-06-16
bitrex <bitrex@de.lete.earthlink.net> wrote:

>Looks like setting it up for the Tiny84 is straightforward these days:
>http://highlowtech.org/?p=1695
>The Tiny84 only has 12 pins, but even that is more than I need. I'd >prefer the larger code space, 8k vs 2k for the 2313. They're both about >the same price in quantity at Mouser.
That makes sense. If you program the uC in C 2 KiB can be used up easyly if you happen to use "printf" or its friends. You also could use linear code more easyly if you need speed for some tasks. -- Dipl.-Inform(FH) Peter Heitzer, peter.heitzer@rz.uni-regensburg.de
Reply by bitrex June 16, 20162016-06-16
On 06/16/2016 06:51 AM, Peter Heitzer wrote:
> bitrex <bitrex@de.lete.earthlink.net> wrote: >> On 06/16/2016 04:31 AM, Peter Heitzer wrote: >>> bitrex <bitrex@de.lete.earthlink.net> wrote: >>>> Is there a CMOS-type substitute for the 74LS47 with "open collector" >>>> type outputs suitable for sinking around 20mA? >>> Although kind of overkill. Perhaps a small &micro;C. The AVRs for example >>> can sink about 20 mA/pin with a total of 200 mA for VCC and GND. >>> Of course the outputs are not open collector. If you need OC and more >>> than one digit to drive a combination of &micro;C and one OC driver can be >>> the solution with the least components. The &micro;C could also do PWM and >>> multiplexing. >>> > >> Yeah, there's going to be a uC involved one way or the other...I'm >> trying to figure if it would be better to just use an AVR with more pins >> vs an 8 pin AVR and an external switch IC. > >> An ATTiny85 that costs under a dollar in quantity plus an external >> switch that costs 25 cents in quantity is a better value than something >> like a Mega168 that costs $1.65 in quantity, as the board size would be >> pretty much fixed by larger components either way. > >> There are other weird AVR devices that seem to use a "Tiny" core but >> have more pins, but I'm taking advantage of the Arduino toolchain and >> AFAIK they're not supported, and I don't really want to take the time to >> write an implementation. > The only supported "Tiny" device is the Tiny85, but the Tiny2313 is not > very different to the Tiny85. > http://playground.arduino.cc/Main/ArduinoOnOtherAtmelChips > mentions the 2313. So it should be possible to use the 2313 with the > toolchain. The 2313 costs about the same as the 85 but gives you 18 > usable pins vs 6 pins on the Tiny85. >
Looks like setting it up for the Tiny84 is straightforward these days: http://highlowtech.org/?p=1695 The Tiny84 only has 12 pins, but even that is more than I need. I'd prefer the larger code space, 8k vs 2k for the 2313. They're both about the same price in quantity at Mouser.
Reply by Peter Heitzer June 16, 20162016-06-16
bitrex <bitrex@de.lete.earthlink.net> wrote:
>On 06/16/2016 04:31 AM, Peter Heitzer wrote: >> bitrex <bitrex@de.lete.earthlink.net> wrote: >>> Is there a CMOS-type substitute for the 74LS47 with "open collector" >>> type outputs suitable for sinking around 20mA? >> Although kind of overkill. Perhaps a small &micro;C. The AVRs for example >> can sink about 20 mA/pin with a total of 200 mA for VCC and GND. >> Of course the outputs are not open collector. If you need OC and more >> than one digit to drive a combination of &micro;C and one OC driver can be >> the solution with the least components. The &micro;C could also do PWM and >> multiplexing. >>
>Yeah, there's going to be a uC involved one way or the other...I'm >trying to figure if it would be better to just use an AVR with more pins >vs an 8 pin AVR and an external switch IC.
>An ATTiny85 that costs under a dollar in quantity plus an external >switch that costs 25 cents in quantity is a better value than something >like a Mega168 that costs $1.65 in quantity, as the board size would be >pretty much fixed by larger components either way.
>There are other weird AVR devices that seem to use a "Tiny" core but >have more pins, but I'm taking advantage of the Arduino toolchain and >AFAIK they're not supported, and I don't really want to take the time to >write an implementation.
The only supported "Tiny" device is the Tiny85, but the Tiny2313 is not very different to the Tiny85. http://playground.arduino.cc/Main/ArduinoOnOtherAtmelChips mentions the 2313. So it should be possible to use the 2313 with the toolchain. The 2313 costs about the same as the 85 but gives you 18 usable pins vs 6 pins on the Tiny85. -- Dipl.-Inform(FH) Peter Heitzer, peter.heitzer@rz.uni-regensburg.de