In addition to a current limiting resistor mentioned by Ricardo, you'll also want to make sure that both the 3.3v MSP430 and the 5V device have their grounds connected. This will make 0V for the MSP430 be the same potential as 0V for the 5V device.

I just finished a project this weekend where I used an MSP430 G2553 to control the power and function buttons of a cheap camera with transistors, and had this exact same problem. I had to add current-limiting resistors, and I have to make sure the emitters and collectors of the transistors were wired up to the buttons correctly. Before I added the resistors, it seemed like my power button/transistor was working, but really I had been shorting through the transistor and the camera was reading the high on the MSP430's pin directly.

For reference, my question from a few days ago.

In addition to a current limiting resistor mentioned by Ricardo, you'll also want to make sure that both the 3.3v MSP430 and the 5V device have their grounds connected. This will make 0V for the MSP430 be the same potential as 0V for the 5V device.

I just finished a project this weekend where I used an MSP430 G2553 to control the power and function buttons of a cheap camera with transistors, and had this exact same problem. I had to add current-limiting resistors, and I have to make sure the emitters and collectors of the transistors were wired up to the buttons correctly. Before I added the resistors, it seemed like my power button/transistor was working, but really I had been shorting through the transistor and the camera was reading the high on the MSP430's pin directly.

For reference, my question from a few days ago.

In addition to a current limiting resistor mentioned by Ricardo, you'll also want to make sure that both the 3.3v MSP430 and the 5V device have their grounds connected. This will make 0V for the MSP430 be the same potential as 0V for the 5V device.

I just finished a project this weekend where I used an MSP430 G2553 to control the power and function buttons of a cheap camera with transistors, and had this exact same problem. I had to add current-limiting resistors, and I have to make sure the emitters and collectors of the transistors were wired up to the buttons correctly. Before I added the resistors, it seemed like my power button/transistor was working, but really I had been shorting through the transistor and the camera was reading the high on the MSP430's pin directly.

In addition to a current limiting resistor mentioned by Ricardo, you'll also want to make sure that both the 3.3v MSP430 and the 5V device have their grounds connected. This will make 0V for the MSP430 be the same potential as 0V for the 5V device.

I just finished a project this weekend where I used an MSP430 G2553 to control the power and function buttons of a cheap camera with transistors, and had this exact same problem. I had to add current-limiting resistors, and I have to make sure the emitters and collectors of the transistors were wired up to the buttons correctly. Before I added the resistors, it seemed like my power button/transistor was working, but really I had been shorting through the transistor and the camera was reading the high on the MSP430's pin directly.

For reference, my question from a few days ago.