liudr:
Thanks Bill. That's right. It's unfair to compare my back pack with their shield. My back pack has an ATMEGA328 so it starts up and recalls back light amount from EEPROM but their shield has no such mechanism. But what about using a depletion mode MOSFET? if the D10 is input on reset, the MOSFET conducts, unless you turn it off by a 5V. Will that solve this shield problem?
There are many ways to redesign the circuit solve the problem.
The final design can potentially be influenced by cost.
mosfets are great, but a mosfet solution will cost more than a simple NPN transistor design.
But then I'm very sensitive to costs as I came from an environment of building products in the 100k/month range.
With that volume, pennies mattered.
--- bill