Serial problem with Pro-mini

Development Tools IDE 1.x
1

Hi, hoping for some help or clarification.

Project overview: I have a GPS receiver connected to an Arduino Pro-mini clone and a 433mhz transmitter via serial. The point of the project is to send GPS location data to a camera equipped with a 433mhz receiver. The pro-mini decodes some basic GPS information to a small display and monitors the battery. To reduce power consumption the Pro-mini has a separate power switch so it is only on when required.

Problem: What I have noticed is when the GPS receiver is on and I have the Pro-mini turned off, the serial data on the Rx pin of the pro-mini is causing the power LED of the pro-mini clone to flicker! Is this normal? It seems like some sort of internal feedback from the Rx pin to VCC.

Thinking there might be a wiring problem, I tried a second pro-min clone board with only a Gnd connection and the Rx pin connected to the GPS module and the problem persists.

Thanks.

2

If IO pins are High and VCC is low, current can flow thru the clamp protection diodes and partially power the uC. That's why the IO pins are not supposed to go above 0.5V above VCC and 0.5V below Gnd.

3

Yes of course.

The Power LED and resistor effectively pull the VCC pin low when you disconnect power. Thanks for the confirmation.