5
\$\begingroup\$

What is the component inside an iPhone selfie stick? Testing reveals it is not a transistor.

photo of PCB and close-up of unknown component

We have done some probing of it and come up with the following:

The mystery 3-pinned component drops the phone’s 2.2V microphone line (between pins 1 and 2) to 0.240V when pins 3 and 2 are connected by a push button.

Connecting it to a component tester (LCR-T4) suggests that it is not a common transistor, but 2 diodes (see schematic).

Inserting 2 diodes and a resistor to mimic the component, does not work, suggesting it is something more complicated.

There are no indications on the oscilloscope, of a ‘chirp’ or acknowledgement ( http://david.carne.ca/shuffle_hax/shuffle_remote.html )

Connecting diodes between pins 1 and 2, does not yield a result. (IN4007, BZX553, Bat43, Bat85)

Connecting various Transistors do not work. (30+ from a bag of assorted transistors)

Connecting a plain resistor does not work. (It would if it were Android)

The mystery component inside the £1 selfie stick, is in an SOT416 package. One model had “G9” on the package, another had it scratched off.

Might it be a smart, proprietary chip? If so, how do I get 100pcs (i.e. not cannibalising selfie sticks)

After much researching, probing, experimenting, and asking everyone I know, we are thoroughly stumped! So thank you, in advance, for your time and help.

\$\endgroup\$
  • \$\begingroup\$ Have you tried different resistor values while measuring the voltage? Your goal would be to get 0.24 V. The SOT416 could be a (very) low Vt MOSFET as well. \$\endgroup\$ – Bimpelrekkie Jan 11 at 15:43
  • \$\begingroup\$ @Bimpelrekkie The diode measurements would indicate that it may be a jfet, not a mosfet; a mosfet would have a gate terminal isolated from the other two terminals. \$\endgroup\$ – Hearth Jan 11 at 16:27
  • 1
    \$\begingroup\$ Could you give a schematic of how things are connected on that circuit board? Just the one photo isn't enough to go by. \$\endgroup\$ – Hearth Jan 11 at 16:29
  • \$\begingroup\$ @Hearth I have jet to see a JFET in such a package, JFETs are also very rare these days. Yes a MOSFET has an isolated gate but if that was really isolated it would be unprotected against ESD and then it would break very easily. Too easily to be of practical use. Gate oxide is extremely fragile. So there are also ESD diodes present one or more of those might be the 2 diodes OP measures. \$\endgroup\$ – Bimpelrekkie Jan 11 at 18:29
  • 2
    \$\begingroup\$ Perhaps you are going about this the wrong way: rather than try to source a part (your mention of 100 pieces) to clone this design, perhaps you should be researching how to make an iphone camera trigger. Such a question wouldn't really be on topic here, but a web search might be fruitful. \$\endgroup\$ – Chris Stratton Jan 11 at 18:51
3
\$\begingroup\$

As I understand the selfie sticks for iPhone use the headset plug to activate the camera. This is the same circuit used to operate the start/stop or possibly mute when listening to music. It works by presenting a change in impedance to the phone. It also clicks the camera. The diodes are simply steering diodes for the switch.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.