Hello Dave, >> Also, in my tests I've found it can be good to have a 100pF >> ceramic cap across latch and GND pins on the last HC595. > While you can get away with not having a bypass for every logic chip, > ANY chip that does a lot of I/O pin loading, or fast switching, needs one. oh, maybe I haven't made myself clear. I have a 100nF cap between VCC and GND pins on each HC595. The 100pF cap I'm refering is an additional cap between LATCH and GND pins on the last HC595. I really want to reduce ripple and any other noise on the VCC line. The ~400uH inductor instead of the 100uH I was using really helped but I still would like to reduce it even further. Let's see what can I do tomorrow. >> I'm thinking about putting one 100pF cap on clock line too. > I wouldn't. This just makes your micro draw more current during the > transitions. Yes, that's right. I've tried it and this messed up everything . > I'd feed that line with a 100 ohm resistor, and terminate with 100 ohms > in series with a 0.1uF cap. > Then scope it on both ends of the track, and adjust the resistors as > needed. Yes again. I've been thinking about termination but haven't implemented it yet. Right now, I have a 2m cable between the controller board (with the PIC18F252) and the LEDs board (with the HC595s). Cable is a 10 (26AWG) conductor without any twisting. Cable wiring is: 1 - GND 2 - GND 3 - GND 4 - 24VDC 5 - 24VDC 6 - Clock 7 - Data 8 - Latch 9 - Enable Cable resistance is about 3ohms (including conector resistance). This is your ordinary RS232 cables with DB9 male/female connectors. DB9 male on the control board, DB9 female on the LEDs board. I don't know the characteristic cable impedance but don't think it's a big problem on this situation. Your idea of 100ohms resistor on the controller board and 100ohms+100nF on the end of the line seens interesting. How would it work? What should I look for when doing those tests? Thanks, Brusque -- --------------------------------------------------------------------- Edson Brusque C.I.Tronics Lighting Designers Ltda Research and Development Joinville - SC - Brazil http://www.ryan.com.br/netiqueta.htm www.citronics.com.br --------------------------------------------------------------------- -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist