# Super Noob Question

Hey, likely a simple question, I'll keep my own conjecture out of the equation;

Lets say you've got a Mega2560 and an Attiny85- each on their own power supply (lets say a battery).

The Mega just need to know when the Attiny pin goes high.

Being on their own power supply; can you just hook the Attiny pin to the Mega pin? When the Attiny pin goes high would this cause any issues in the Mega?

I only ask because of the independent power on each is something I have no experience with. . .

Thanks!

Both running from same battery voltage, 4.5V?
Connect gnds together. Then Mega can read high/low from Attiny directly.

Aha. But, being both on separate power as I stated. . .

However, what if I connected a transistors collector and emitter to two pins on the mega- then the attiny to the base? The mega turns the collector pin high, waits for the attiny to activate the base for the emitter pin to go high.

No grounds can be connected.

Fun problem, eh?

Hi,

No grounds can be connected.

No, the grounds are connected
OR
No grounds can be connected, that is they are not connected together. If so why?

Post a diagram of what you are trying to do, including gnds and power supplies.

Tom..

rutilus:
Aha. But, being both on separate power as I stated. . .

However, what if I connected a transistors collector and emitter to two pins on the mega- then the attiny to the base? The mega turns the collector pin high, waits for the attiny to activate the base for the emitter pin to go high.

No grounds can be connected.

Fun problem, eh?

If you cannot connect a common ground then I would go with an optical isolator. Something like a 4n25.

The input from the attiny connects: input to atTiny output pin, AtTiny gnd to gnd on Left.
Mega Gnd to Gnd on Right, Mega input to 10k resistor on right.

Chuck.