Thanks for the repsonses, see comments below. On 13 Sep 2011 at 22:22, Mark Hanchey wrote: > Add a zener diode on each of the 3.3V, +5V, RXD and TXD lines so it=20 > clamps the voltage at whatever is safe for those pins Similar to d) below > Put a 10K + resistor across +12V power rails so that when the +12V batte= ry > power is removed those capacitors self discharge quickly enough to preve= nt=20 > someone from plugging in another board before they discharge normally. Yes, not a bad idea, but battery powered means I'm reluctant to add waste p= ower=20 unnecessarily. I think capacitor charging current is more likely the cause = of the=20 problem. > Also consider adding an LED to the board near the connector that shows=20 > when the board is powered to remind people when plugging in another board= .. Clever, but in as it's battery backed (12V 2AHr) even an LED @ 1mA or so wo= uld=20 waste too much power. On 13 Sep 2011 at 20:56, Josh Koffman wrote: > Ok, I'm definitely not an expert in this area, but would a diode on > the 3.3V line in between the connector and the rest of the circuit on > the daughterboard help? Yes, it would help, but affect other things, see c) below. On 13 Sep 2011 at 22:17, Isaac Marino Bavaresco wrote: > a) Ensure the ground connection connects before any other signals, > perhaps making it longer or using a special connector; Yes, will try to achieve that with standard 0.1" head pins by leaving the G= ND pins=20 slightly higher.=20 > b) Put a series resistor (between 33R and 100R for fast signals, more > for slow signals) in each logic signal that crosses from one board to > another; Good idea. The only signals are TXD and RXD, running at about 900kbaud, tra= ces=20 maybe 100mm long, could try 100R. > c) If possible, put a diode in series with the power signals; I'll consider that a bit more. I have +3.3V and +5V analog supplies derived= from the=20 power signals - will have to think through exactly what this will affect an= d by how=20 much. > d) Put a TVS from each signal to ground. Would have to be on the main board which is less desireable to modify. Clam= ping=20 voltage likely not be close enough to be effective.=20 =20 Thanks again. --=20 Brent Brown, Electronic Design Solutions 16 English Street, St Andrews, Hamilton 3200, New Zealand Ph: +64 7 849 0069 Fax: +64 7 849 0071 Cell: +64 27 433 4069 eMail: brent.brown@clear.net.nz --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .