| ??? 08/01/06 21:13 Read: times |
#121526 - the wiring is simpler with ST2221A (equivalent) Responding to: ???'s previous message |
As an enduser, you can see Erik's point, he only needs 3 wires to talk to his LEDS, the rest is wiring. At the other end of the power interface TO the LEDS, saving wires is a nice thing, and the scheme is very clever, if tricky to implement.
With the ST2221A or similar chips (Rohm, Allegro, 74xx shift registers and more), were you to use it for segment displays, you can make a miniboard with a chip and a 7 segment LED and just 5/6 wires: Vled (can be Vcc), Vcc, Gnd, Clk, Data in, data out, Strobe. I just had a look at the datasheet for Charlie chips, the max segment drive is 30mA and 30mA/8 is a meager average of 4mA per segment. Even a dirt cheap Hc shift register/latch can do 9 times better than that at $0.15 per digit = total $1.20 for 8 digits. http://www.fairchildsemi.com/ds/MM/MM74HC595.pdf Erik PS No, I am NOT saying never multiplex, just do not choose multiplex without thinking. PPS for really large displays Allegro now has a 'skewed' chip in the 2221 style that virtually eliminated EMI. |
| Topic | Author | Date |
| reduced pin count multiplexing | 01/01/70 00:00 | |
| with e.g. ST2221A you need 3 pins | 01/01/70 00:00 | |
| No you are right Erik | 01/01/70 00:00 | |
| Well | 01/01/70 00:00 | |
| the wiring is simpler with ST2221A (equivalent) | 01/01/70 00:00 | |
| was it somone named Charlie ... | 01/01/70 00:00 | |
| ??? | 01/01/70 00:00 | |
| check out the appnote.. | 01/01/70 00:00 | |
| Reading the appnote always helps | 01/01/70 00:00 | |
| anyway | 01/01/70 00:00 | |
| who is he? | 01/01/70 00:00 | |
| walking through the description give you a charlie | 01/01/70 00:00 | |
| Small but real benefit | 01/01/70 00:00 | |
| who does your soldering? | 01/01/70 00:00 | |
| A billion dollar assembly house | 01/01/70 00:00 | |
| very small compared to | 01/01/70 00:00 | |
| Statistically or not | 01/01/70 00:00 | |
| I strongly disagree | 01/01/70 00:00 | |
| blah | 01/01/70 00:00 | |
| deterministic vs predictable | 01/01/70 00:00 | |
| and i know | 01/01/70 00:00 | |
| yes, but I am not talking about kettles | 01/01/70 00:00 | |
| just a minute, there, pilgrim ... | 01/01/70 00:00 | |
does not matter when they will happen eventhough ' | 01/01/70 00:00 |