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[on:]

I am trying to use an ATtiny84 to "press" the shutter/button on the hackHD. From my understanding of how the shutter/button works you have to pull it to ground (pin5) correct me if I am wrong. So what I am planning on doing is build my circuit like illustrated in the picture attached... Does it look like it would work?

1-ATtiny84
1-hackHD
1-NPN Transistor 2N3904   https://www.sparkfun.com/products/521
?? 1-4k7 resistor (Im not sure if I need this??)

Thanks for your help!

[Reply #1 on:]

HackHD Pins 3 and 5 (GND) are usually shortened by a button, according to the linked manual, so the 4k7 resistor is not required where you draw it.
But I'd add a resistor between attiny and transistor base. 
I guess your 4k7 might work. Depends on the pullup resistor, which is obviously built into the HackHD.

I bet dhenry would say you can even do without transistor and resistor:
simply connect the attiny output  to   3  attiny GND to  5 and set output to low for active.
I understand there's no warranty on neither a hackHD nor an attiny45, so just give it a try
If you're timid, you may measure the voltage of Pin3 and the current flowing between  Pin3 and Pin5 through a DMM first.
Should be about Vcc and very few mA.

[Reply #2 on:]

Thanks michael_x I will try it as soon as I get the camera!! Just placed the order last night should hopefully get it soon after Christmas!! :-)

[Reply #3 on:]

Great camera! Just connect the Pin3 on the HackHD directly to a digital pin on the Arduino and like Mike said make it go low, but then make it go high after after say 100-200ms to complete the "button push". Unless your turning it off or on then you would want it to stay low for a couple seconds before making it go high again, forgot the exact timing. If your new to arduino, just modify one of the example sketches to turn on an LED on pin13.

[Reply #4 on:]

Awesome!! Thanks for the input it's supposed to be coming in the mail today so I will give it a try!