I noticed an interesting result with an 'arduino-compatible' pro mini i bought from ebay (http://www.ebay.com/itm/150823081225?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649). I am using it with a ds18b20 for temperature measurements. It works fine as long as it is connected to the computer's usb. When I disconnect the FTDI board and let run on a seperate power source, the lcd prints read "185" which is clearly wrong. With further tinkering, I found that the arduino will reset and read acceptable values from the sensor by simply touching the "GRN" pin with a short jumper wire that is connected to nothing else. So my question is: what does the GRN pin do?
Hi
I think it refers to the markings on the FTDI board - which have Green and Black ends for the green, yellow, orange, red, brown and black wiring that run to each of those pins.
On my FTDI breakout, green is marked as RTS so that's what the pin is. That's part of your serial communications so will have to leave it to more knowledgeable folk as to why that might cause a reset when connected to a piece of wire...
Cheers ! Geoff
It's DTS which controls the auto-reset function. Touching a piece of wire is coupling enough energy to cause a reset.
The board you are using probably relies on reset's internal pull-up which may be weak enough to still allow some floating to occur.
Thank you James, very helpful. Would a capacitor connected to ground help to bring DTS low initially causing a reset? And any idea why the board must be reset (after being plugged in to external power) before it can return a temperature measurement from the ds18b20?
On some breakouts, the green pin is the DTR pin (as on the one I have).