Hi I would like to use a shift register to drive 4 digits 7 segments leds (1"). Which type of shift register is more suitable? Can 74HC164 provide more current? As I tried using 74LS164, it is unable to supply enough current.
Thanks
They are not very different at pulling low, though the LS164 is poor at pulling up. Did you use the 74LS164 in low active mode (LED on when output is low)?
The 74ACT164 has about 3 times the pull low capability of the 74HC164, but is a little hard to find in a DIP package.
ok
Probably a 74HC595 since it has a latch input.
Yes, it can "source" or "sink" about 20mA or so.
Right, it can only "source" about 2mA, but it could "sink" 16mA or so. This would likely be plenty for you, you just need to use common anode LEDs.
Plenty of those can be found in the ULN series.
-- Regards, Joerg http://www.analogconsultants.com
How much current do you need? Are you using some cheap-ass LED display that takes a lot of current?
Some of the best SRs for this sort of application would be those from TI's TPIC DMOS line, which are essentially HC595s with open-drain MOSFETs (good for up to a few hundred mA each, depending on model etc.) on each output line.
Or just add some drivers to an inexpensive HC595 and go with that.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
I suggest you look at MAX7219. It will drive up to eight seven-segment LEDs in a multiplexed display or 64 discrete LEDs. It has an SPI compatible input and is a single chip solution to your problem.
-- John B
-- http://www.allegromicro.com/en/Products/Part_Numbers/6275/6275.pdf
I second the MAX7219, neat part if you can get em. As an alternate I have used a 595 and a UNL2003 as a driver. Plus a little glue to place it on a spi bus.
Cheers
Plenty of them here:
-- John B
It does help to know the VF of the segments, I know it's such a small detail, easy to overlook. The LS at 5V should be able to at least light them up, maybe a problem with uniformity across several chips, but...
View in a fixed-width font such as Courier.
. . . . . . Vcc-----+----------------------------------------+----- . | | . +---------------LS164--------------+ | . | | | | . | | | | . | +----------------. | | . | | | + | + | . | | | | | . | [8k] [120] 4-V | Vcc-V [Rc] . | | | F | F | . | | -.----+ - | | . | | 0.5 | | | - | . | | + |/ | | | . | +---------| | | | . | | ^ |> | | | . | | Q1 | |/ | | . | | +--| | | . | | | |> | | . | [4k] Q2| | | . | V + 1.5 | | | OUT | . | F '----+-----------|-----------+ . | | | | | . | | | | + | . | | |/ | --- . | | ---| | V \\ / . | | |> | F --- . | | | | - | . | v | | | . +----------------------------------+ --- . | /// . --- . /// . . . . .
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