DIYEFI.org Forum

I figured we should bring up this monitoring thing. I believe the MCU has on-board watch dog and brown out, but what about other features. I see SECU3 uses this interesting Maxim DS1811-15 chip. It delays 150ms before passing power to the MCU, allowing the power supply to solidify before powering up fully. Are there thoughts, concerns, or other ideas relative to MCU monitoring?

In my (quite personal) opinion, a good design doesn't need a watchdog timer.

About the brown out, I don't see it in the datasheet. The MCU has power-on reset based on the voltage seen in the reset pin, though. Keep in mind that if the cpu is constantly powered, the power supply transient happens once in a while. And if you see an out-of-tolerance power supply condition during normal operation, I wouldn't like to have the cpu irremediably dead for 150ms, I prefer the power-on reset behavior.

The power-on 150ms could be obtained from an RC circuit connected to the reset pin, so the pin is held in '0' until the capacitor gets charged.

What I like about it is that it is very small and easy to put in any design.

+1 marcos, however there is no harm in implementing a watchdog/COP monitor. I intend to eventually. I initially thought it had to be within a window, and didn't like that, but you can just have it setup for "before X ms" which is fine. One day, after everything else. It costs nothing to have it there.

+1 means NO way for 150ms
+1 means good design = cop unrequired

However, I think there is a brown out ISR. I've used it and posted about it.

Fred.