How to pull down signal in external circuit

[frenky]

So I have this old compact camera Pentax Optio W60:



I would like to control it with arduino (or attiny85).
All I need is control 3 switches: power on, half press and full press of capture button.

I already took it apart and all 3 switches pull signal to the ground when in contact.

So how do I pull down signal with arduino without risking the damage to the camera circuit?

My ideas:


In top image I would make D5 output pin with 5V on output. And then output 0V (LOW) when I wanted to pull the camera signal down.
In bottom image D5 would be normally at 0V and changed to 5V (HIGH) when I wanted to pull down the camera signal.

What would be the most correct way to do it? (Please consider that D1 and D5 are most likely at different potentials when HIGH.)

Tnx.

[Zero999]

It's quite likely both circuits will work.

The first one, with the diode will probably work because the camera will most likely have a high logic level threshold, less than your MCU's power supply + a diode drop and a low logic level threshold above a diode drop.

The second one, with the MOSFET has the greatest chance of working and would be my first choice.

[frenky]

Thank you.

[frenky]

It's not pretty but it works.