Post by thread:[EE]: 74LS164

Hello, I'm wanting to use three 74LS164 to turn on/off 24 leds. Is it possible to use just two PIC outputs to control various cascaded 74LS164? I mean, wiring the Output7 from the first to the DATA input of the second and so on. Any experiences about this? Thanks, Brusque ----------------------------------- Edson Brusque Research and Development C.I.Tronics Lighting Designers Ltda (47) 323-2138 / (47) 9993-6453 Blumenau - SC - Brazil http://www.citronics.com.br ----------------------------------- -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Edson Brusque wrote: > I'm wanting to use three 74LS164 to turn on/off 24 leds. > > Is it possible to use just two PIC outputs to control various cascaded > 74LS164? I mean, wiring the Output7 from the first to the DATA input of the > second and so on. Any experiences about this? I have used a similar approach where the QH of one device was connected to both the A and B inputs of the next device. The outputs were connected to LEDs such that a LOW on the output would light the LED (since the devices cannot source much current). The LEDs were updated by shifting bits into the register quickly. This scheme worked very well, using only a data and a clock to drive the shift registers. Make sure you take into consideration the current requirements of the LEDs when selecting devices, since the 74LS164 has a max recommended IOL of 8mA. David W. Gulley Destiny Designs -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> > Is it possible to use just two PIC outputs to control various cascaded > > 74LS164? I mean, wiring the Output7 from the first to the DATA input of the > > second and so on. Any experiences about this? > Make sure you take into consideration the current requirements of the > LEDs when selecting devices, since the 74LS164 has a max recommended IOL > of 8mA. I have checked for the 74xx164 parts but in most cases the 74HC and 74HCT parts have very similar Iout low current specs and much lower quiescent current specs (typically under 1 mA compared to about 20+ mA for the LS part). The prices are generally about the same or cheaper than LS. LS was a fine logic family in its day but it's day has gone. Using a CMOs equivalent is preferable unless there is a very good reason to use LS (like perhaps having a drawerful of them? :-) ). Russell McMahon . . -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> I'm wanting to use three 74LS164 to turn on/off 24 leds. > > Is it possible to use just two PIC outputs to control various cascaded > 74LS164? I mean, wiring the Output7 from the first to the DATA input > of the second and so on. Any experiences about this? The 164 advances on the L-H clock transition. Depending on the app and data you may need to invert the signal from q7 and the CP of the next 164 -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

>> I'm wanting to use three 74LS164 to turn on/off 24 leds. >> Is it possible to use just two PIC outputs to control various cascaded >> 74LS164? I mean, wiring the Output7 from the first to the DATA input >> of the second and so on. Any experiences about this? >The 164 advances on the L-H clock transition. Depending on the app >and data you may need to invert the signal from q7 and the CP of the >next 164 Better use the good old 4017, 10 outputs and just a clock input. :o) -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> The 164 advances on the L-H clock transition. Depending on the app > and data you may need to invert the signal from q7 and the CP of the > next 164 My mistake - I'm working on a 12-digit driver using 4017s/ULN2003s and got carried away. ISTR that this was asked some time ago. You'd connect CPs together and MRs together and q7 -> Data. But I also recall that someone tried this and lost data bits, don't remember why I recently made this display http://home.clear.net.nz/pages/joecolquitt/2wireled.html on which I found it was not necessary to explicitly use the 164's MR -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

I don't see why that would not work for LED's, but I think you should look for something with latched outputs, like the 74HC595 or similiar, that way you won't get glitches when updating the outputs. However an extra line is required to strobe the latches. Past experience has shown that you usually can combine this with some other function, so it doesn't cost you an extra pin after all :-) {Quote hidden}>Hello, > > I'm wanting to use three 74LS164 to turn on/off 24 leds. > > Is it possible to use just two PIC outputs to control various cascaded >74LS164? I mean, wiring the Output7 from the first to the DATA input of the >second and so on. Any experiences about this? > > Thanks, > > Brusque > >----------------------------------- >Edson Brusque >Research and Development >C.I.Tronics Lighting Designers Ltda >(47) 323-2138 / (47) 9993-6453 >Blumenau - SC - Brazil >http://www.citronics.com.br >----------------------------------- > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics Ray Gardiner spam_OUTrayTakeThisOuTdsp.com.au [ 2001 ] -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> Hello, > > I'm wanting to use three 74LS164 to turn on/off 24 leds. > > Is it possible to use just two PIC outputs to control various cascaded > 74LS164? I mean, wiring the Output7 from the first to the DATA input of the > second and so on. Any experiences about this? > > Thanks, > > Brusque This will work fine, with one possible problem: The Q7 output of each '164 is driving not only an LED but also the next '164. Depending on the LED current, the Vol of this output may rise too high to give you a good noise margin into the next '164. Of course, your LEDs will be connected, via a resistor from +5V to the outputs of the '164. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> I don't see why that would not work for LED's, but I > think you should look for something with latched > outputs, like the 74HC595 or similiar, that way you won't > get glitches when updating the outputs. However an extra > line is required to strobe the latches. Past experience has > shown that you usually can combine this with some other > function, so it doesn't cost you an extra pin after all :-) Depending on the update rate of the LEDs you will _not_ see any glitching. The '164 will do the job just fine. (But the '595 is a nice chip). Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics