Bootloader failure....

I have a project where I need to have an external reset switch to reset the Arduino.
I killed three Arduino boards before I realized it was the reset switch that was
killing the bootloader. I had a N/O mometary switch between the RESET pin on
the Arduino and GND. After killing the fist two boards I added a debounce circuit
thinking maybe it was a glitch or something doing but I just killed another
board. The debounce circuit is attached…

Why would performing a reset clobber the bootloader ?

reset.jpg

Performing a reset shouldn't clobber the bootloader. You've obviously got something screwy. But you've decided only to make your claims and have provided absolutely no way for anyone to look at any part of your project. How the hell you think anyone would be able to figure out what is wrong without being able to see is beyond me. But lots of people use the reset pin and it doesn't kill their bootloader. So it must be something to do with your particular project.

"no way for anyone to look at any part of your project" ?? I could send pictures of
the Arduino with wires plugged into it. Not sure what you would learn from that. I've been
using Arduinos for years. Maybe it isn't the bootloader that is failing - thats my assumption.
My project consists of an original Arduino R3. It has an iSYST LMXShield to drive
(3) 3208 LED Matrix displays. The shield does not use the reset pin... it simply provides a
feed thru it.

My project works fine, even resetting when I use the external switch as described.
HOWEVER, when I go to upload an updated sketch, the IDE->Tools->Port is grayed out
even though there are several COM PORTs correctly defined. Prior to using the switch
I can upload sketches just fine. But after I use the switch to reset the project, I can
not do any more uploads. If I remove the shield the Port is still grayed out. If I
replace the Arduino board -- changing nothing else, it successfully grabs a Port and
loads sketches just fine.

An external reset switch between reset and ground should not cause any problems - that's the same thing as the reset button. It also doesn't even touch the usb-serial chip which is what fails if you lose the COM port...

The 16u2 on the official boards is fairly fragile (the clones are much harder to damage) but without knowing what you have connected how, I couldn't venture a guess at how the perfectly innocent reset button appears to be associated with damaging the serial chip

miker:
"no way for anyone to look at any part of your project" ?? I could send pictures of
the Arduino with wires plugged into it. Not sure what you would learn from that.

Or you could be a bit more intelligent than that and post a wiring diagram and the code. Then maybe someone could see what you've done wrong.

I've been using Arduino for many years too. But I don't think that I get it perfect every time. Even I make mistakes once in a while. At least I'm smart enough to know that people would need to see my mistake to find it.

A thought - could it be that the way you have things mounted, pressing the external reset switch physically presses something such that it shorts? There have been problems where the bottom of shields shorted against the USB connector.

Could the shield do something screwy if the controlling board is in reset state (all pins tristated, hence potentially floating)? I'm not familiar with that shield

PROBLEM RESOLVED.... all suggestions were good ideas; however, had a bad USB cable -- able to deliver power to UNO but I guess not the data signals. :confused: Thanks to all who responded....

Well, that would do it.

There has been a real plague of bad USB cables in the Arduino community. I'm pretty sure one or more arduino kits (probably clones, not official kit) are being sold with garbage cables, with data lines either absent or very prone to failure.

I've had bad USB cable for the last few years. By default I throw away any USB cable that comes in clone kits, they are often too short anyway, and use an old one that came with my scanner 20 years ago (geez I am old, I remember when USB 1.1 was new stuff)