BasicMicro - Forums

This may seem to be a none issue, but my application relies on initialization for proper operation and safety. The issue is that when I power down the pcb and the usb2ser adapter is connected (for monitoring purposes) the nano program starts running again on a very low voltage (1.4vdc). This voltage can be read with all power connectors disconnected except the usb2ser. I would have thought that the nano chip would not run with such a low voltage. The program depends on an initialization sequence that is run on every power up. Since the program continues to run with usb2ser adapter connected I don't get the initialization sequence which can cause some problems with the servo sequencing on startup. It may be a problem I can live with, but it would be nice to have the chip shut down when outside power is disconnected. I know the usb port is powered from the computer and it must be feeding thru the gnd pin and either the res pin or the ser pin. Any ideas on how to drop this voltage from the port?

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Harley

Double check how you are reading the voltage. The Nano chips have a brownout that activates at 2.1v. The USB2SER can provide 5v(from the USB port) so it looks like something else is dragging this down.

Also you can setup your PC side app to hold the nano in reset by setting the RTS pin of the serial port when you want it to be powered down. There really isn't any other option. The nano chips are PICmicro based and PICmicros can run off power from other pins besides vcc. In this case I suspect its getting it from the reset pin (USB2SER is holding it high).

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Tech Support
Basic Micro - Robotic Technology Evolved

I have tried setting the RTS pin on the serial port and that works perfectly for my app. The program no longer runs when I power down the nano and enable the RTS pin in the VB program. It is a work around that will do the job. Thanks!

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Harley

No problem. The only other option would be to hold the TX pin from the PC in a break state. This should make the TX pin to the Nano from the USB2SER board be low. I suspect the TX pin is being held high and the nano, which requires very little power to run, is getting enough from the USB2SER TX pin to do so.

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Tech Support
Basic Micro - Robotic Technology Evolved