sensing ground pin from another arduino

Hi guys, I'm really a noob when it comes to circuit. I'm making a fencing sport scoring system. I need a port in the first arduino to sense the ground port of the second arduino. I can do this with both arduino on usb. But when I put them on 9v batteries, the first arduino can't detect it. I guess it has to do with floating ground and I have no idea how to overcome the problem. Thanks in advance for any head up.

regards

A wire run from the Arduino #1 board ground terminal to the Arduino #2 board ground terminal should do the trick.

Lefty

lefty, I think he means that one swordsman will wear Arduino A, and the other swordsman will wear Arduino B, and some kind of buzzer will ring if the two touch (sword to armor). Maybe you understood that, but the wire would have to connect the swordsmen through the mat or through a central box on the sidelines.

Without some wire joining the parties, this is not a trivial detection circuit. Two circuits cannot detect each other just by touching one contact without some other common potential from which to base a comparison.

thanks lefty for quick reply. as correctly pointed by halley, I'm not in the luxury to connect a permanent ground-to-ground wire between arduinos. will serial-like communication doable as a sensing mechanism? ie. if arduino 1 received some serial communication from second arduino.

Regards,

thanks lefty for quick reply. as correctly pointed by halley, I'm not in the luxury to connect a permanent ground-to-ground wire between arduinos. will serial-like communication doable as a sensing mechanism? ie. if arduino 1 received some serial communication from second arduino.

Regards,

No, without a common ground path (wire) between both Arduinos ground signal, no direct electrical signal connection between the two Arduinos will work, that includes digital, analog or serial connections. Now the common path could be that they both electrical connect to a common mat that both are in electrical contact with, however if that is also the signal & detection path then that won't work for both.

I assume both Arduinos would be battery powered? If not and an AC outlet is being used by both players to power wall power modules then another wire connecting both Arduino's signal ground to the AC outlet ground terminal would satisify the common connection requirement.

Only way around that would be some kind of wireless communications path between the two Arduinos or possibly some kind of optical transmit/receive detectors.

Lefty

Didn't this come up a few months ago:-

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1234807632/3#3

Hey, I have "almost" the same question. If the other arduino cannot detect ground, can an INPUT pin from Arduino A detect an OUTPUT pin from Arduino B? Or is it just the same problem: cannot be detected because they don't have a common ground?

Or is it just the same problem: cannot be detected because they don't have a common ground?

Same case. Take for instance a simple digital voltmeter. You can't take just one probe wire and touch it to a wire and expect to be able to measure the voltage. Voltage potential is the voltage seen between two points, most commonly one of those points is called ground or common.

It's would be like trying to clap with only one hand :wink:

Lefty

hmmm bare feet metal field anyone?

I think you should disregard the suggestion that had wires from an AC outlet connected directly to player's bodies.