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I am working on a headphone circuit that plugs into an iPhone , between the mic wire and the GND wire there is the mic , and a push button , with iPhones when you press the button once it will pause/play music , twice will skip too the next song , and three times will go too the previous song , this is all done with one button , however I want too implement 3 buttons for previous song / play-pause / next song , is there any way to implement a button trigger delay so that when I press the forward and reverse button , it will send a signal to the phone that it has been pressed 2/3 times , is there any way of putting in a delay , thanks UPDATE: I have found a step up module from 0.8v too 3.3v , does anyone know how much current I can draw from a 3.5mm socket and whether this will be enough too power a small micro controller such as the Arduino pro mini ? Thanks

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    \$\begingroup\$ If I understand right, you want to have two extra button that automatically produces two and three button presses respectively? I would use a tiny microcontroller for something like this. It would be simplest and smallest. Check out the 8-pin PICAXE. It's made to be cheap and easy to use and program. You can even use flow-charts and not code if you feel like it. \$\endgroup\$ – DKNguyen Feb 20 at 20:57
  • \$\begingroup\$ The problem with this approach (and any other I can think of) is you will need to get power to the circuit somehow. Unless you literally build your own mechanical switch that makes and breaks two or three contact points on the way down as you push it. \$\endgroup\$ – DKNguyen Feb 20 at 20:59
  • \$\begingroup\$ I have thought about using an Arduino pro mini too monitor button inputs and output the different presses , however there is only about 0.8V on the mic line so I will be struggling too power the micro controller \$\endgroup\$ – jackv12333 Feb 20 at 21:01
  • \$\begingroup\$ There are ATtiny and PIC10 microcontrollers available in 6 pin SOT23 packages that you could use for this to minimize size, but none will operate below 1.8V, so since you need a supply, you couldn't use a single button cell, you'd need two, or a single CR2032 or similar battery. \$\endgroup\$ – Phil G Feb 20 at 22:49
  • \$\begingroup\$ Thanks for the help , thinking about it I could use a micro controller with a small battery within the casing , however the micro controller would have too be very low current because I would need the battery life too last long , any thoughts on which microcomtroller I could use too do this , I would need 1 analogue input for the three different buttons and 1 output for the output pulses , I am thinking about a 3V supply with a very low current draw \$\endgroup\$ – jackv12333 Feb 20 at 22:54
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The voltage on the mic line is the bias voltage for the electret mic element. I think it comes through a 2.2K or 2.7K resistor. There is not enough current available there to power anything. You're only option is an external power source. One lithium coin cell should last a long time.

Separate from that, your two circuit options are a small batch of CMOS chips or one of the ultra-low-power microcontrollers (PIC, AVR, etc.). If the uC doesn't not have an open-drain option for a GPIO pin, you'll need one external FET like a 2N7000.

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