74hc595

MR

I ran out of pins on the Basic Stamp 2P40. I need to drive common anode 7 segment displays, is it possible to use a 74HC595 shift register to accomplish this purpose? If it is possible do I need a different type of transistor? I use common anode displays and currently I have the 3906 transistors.


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If it Stinks it is Chemistry
If it is Mushy its Biology
If it doesn't work its Physics

Mike Green

The 74HC595 outputs are very similar to the Stamp's outputs. Maximum current for any one pin is 20mA and maximum overall current for the 8 pins is 70mA according to the datasheet. One thing to watch out for is the initial condition. There's a Master Reset pin which sets all the outputs to LOW which will turn on the 2N3906 transistors. This is different from the Stamp's initial pin states (which is input mode). If you don't use Master Reset, some pins will start in LOW state and some will have HIGH state.

MR

Thanks.

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If it Stinks it is Chemistry
If it is Mushy its Biology
If it doesn't work its Physics

Forrest

FYI there's a circuit example and code on how to operate 8 LED's from a 74HC595 in the Stampworks Manual available here www.parallax.com/Portals/0/Downloads/docs/books/sw/Web-SW-v2.1.pdf

MR

Thanks Mike, Forrest. I will let you know how it turns out.

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If it Stinks it is Chemistry
If it Gooey its Biology
If it doesn't work its Physics

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hmlittle59

I'm starting to use this part now to drive RED/GREEN LEDs, and this information has been very helpful. thanks

thanks for the info

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hmlittle59

Craig Eid

Texas Instruments has a high power 8 bit shift register - TPIC6595 - with onboard drive transistors. It is a low side drive part that can handle 250mA per pin, steady state, priced at $2.50 at Digikey. See the·attached datasheet for more details.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-1954-5-ND

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························ Craig Eid


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Post Edited (Craig Eid) : 3/22/2009 7:38:31 PM GMT