Hi Charles, as your investigation shows -- the ringing is most likely the problem... several possible fixes: 1. series resistance to slow the rise and fall slew rate --- start with 200 ohms -- can split between PIC and 74HC14 if that helps 2. pull up resistor (5K) on the input of the 74HC14 -- might change the terminating impedance enough to dampen the ringing -- also the input high (1) threshold of HC (even the Schmitt trigger) is a might be a little marginal for the PIC to drive 3. small ferrite beads on each end of the signal one or a combination should work Ken -----Original Message----- From: cflat@ev1.net To: PICLIST@MITVMA.MIT.EDU Sent: 6/30/02 2:31 AM Subject: [OT]: TTL Transmission Hi, I am out of my knowledge zone and thought I would pose this senario to the minds of this list for help. I have a PIC16F877 that outputs a pulse of 200us duration every 2ms (500Hz pulse). I need to send this pulse up to 350 feet down a cable. This cable has 3 conductors that aren't twisted (have no choice but to use this cable, more wires not an option) which are 18awg stranded. Two of the wires are carrying 24V dc and the 3rd wire should carry the pulse. The pulse is ground referenced to the positive 24V lead. I have 5V on the receiving PCB also referenced to the 24V positive wire. When looking at the pulse on the scope, it is a nice clean 5V square pulse coming off the board. At the other end of the cable where it is received by another circuit board, it has a slight bit of ringing on the 0 to 5V transition and has a lot of ringing on the 5v to 0v transition. I had a 74HC14 on hand and put it on the receiving PCB and connected the signal through 2 gates but it didn't help. I think the ringing is too great a level. If anyone knows a good way to get a clean signal or clean up the signal I'd be greatful for help. I've been searching the net for info and it would seem a differential method would be preferrable but I don't have an extra wire so its not an option. Thanks for any help. Charles -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu