On Mon, 11 May 1998 17:42:03 +0100 John Midgley writes: >1) A nice, straightforward BCD to 7-segment decoder chip. I'm doing >this in >code at the moment, but that takes lots of pins. > >2) (On a related note...) a serial in, 4 bit parallel out shift >register. If you are just going to connect the shift register to the decoder, forget the decoder and shift out the data for all segments to a 7-bit shift register. The number of PIC pins is the same. The PIC software would convert BCD to 7-segment and shift it out. Besides not needing a decoder chip, the PIC would have individual control of all 7 segments so patterns other than numbers could be displayed. 8-bit shift registers are common. The 74HC164 is about as basic as they get. Its major limitation is that the data in the register flows directly to the output pins. While you are shifting in new data, the output pins will assume unwanted states. If you shift fast enough, they won't be visible on the LED. Or you could turn off the LED's power supply while shifting. More advanced shift registers have latched and/or tri-stated outputs. >I've browsed various manufacturers Web sites, and become thoroughly >confused - even a single manufacturer seems to produce a bewildering >number of variants that all seem to do the same thing. There are a large number of variants of the 74HC164. They all have the same effective logic (an 8-bit shift register), but the internal circuitry is different. This causes variations in the performance such as speed, acceptable input voltage, supply current, and output current and voltage. For this LED application, the output ratings are most important. For example-- 74HC164 - silicon gate CMOS - similar to PIC chip 74HCT164 - similar to HC164 - different input voltage limits 74C164 - old version with metal gate CMOS - slow. 74LS164 - old version with low-power TTL logic - high Icc. 74164 - very old TTL logic version - even higher Icc. and so on. But all of them will plug into the same socket and work approximately the same if the rest of the circuit can stand them. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]