PropBOE on ext power stops when pulling USB cable

MJB

I have a strange behaviour with a PropBOE.

- I run it from external power (wall wart / barrel connector) -
- power switch set to 1
- USB/serial connected with TeraTerm
- running Tachyon blinky to blink just one LED
- both green power LEDs are on

when I pull the USB cable the blink stops
- both power LEDs are still on

This is the minimum setup to produce the problem.
Actually I have a data logging application to SD that from time to time
I want to plug in and check some status.

I put on the scope and did not find any power drop when I pull USB out.
Had a quick look at PropBOE schematic, but didn't see a reason.

Anybody an idea what to check next / any known issue?
Is there a reset triggered, when USB power stops ??

Thanks
Markus

Mike Green

This is a known behavior that's common to most USB microcontroller interfaces. When you "pull the plug" on the USB connection, there's a short reset pulse produced as the DTR control line floats. There's no easy fix on the PropBOE. If you were designing your own board, you'd simply put a jumper or switch between the Prop's reset line and the collector of the reset transistor in the DTR interface. Switch or jumper open ... no reset when you remove the USB cable or close the USB serial port. You do need this connection for programming.

MJB

Thanks Mike,
I will try with an active USB hub in between to keep the power up.
We'll see if it helps.
I just want the prop to keep running and want to look into the
Terminal every now and then to see what is going on without stopping the logging.

Actually the reset would not be needed at disconnect,
when the board is kept powered externally.

msrobots

I really dislike the USB on every board. But I do understand the reasoning why everybody puts them there.

For me a couple of prop plugs and no USB on the boards is way better. I am missing them old 5-pack Proto Boards without USB. But since USB seems mandatory nowadays Parallax (and other Vendors) should do it right like on the Spinneret and provide a jumper to enable/disable programming by disconnecting /RST.

two pins and a jumper should not really cost much money.

Enjoy!

Mike

Publison

msrobots wrote: »

I am missing them old 5-pack Proto Boards without USB.

You mean these:

https://www.parallax.com/product/32212

You can still get a 5-pack for 99 bucks with the 5+ discount, ( buy four, get on free).