How to get power out from a smart phone?

[rahul_sabnani]

Hi, is there a way to get the power out from a smart phone? i wish to power a device on using a smart phone as i would at the end interface the device with the phone. so i do not wish to use an external battery for the device and infact somehow use a smart phone to supply power to the device?
does anybody has any idea how to do this?

 

[berkeman]

What's a smart phone? You mean a cell phone? I don't know what the typical charging circuits look like, so I don't know if you can pull power back out of the charging jack. Sounds like a good way to hurt your phone.

 

[rahul_sabnani]

smart phones are cell phone with internet and other advance features. i wish to find a way that could help me get power out from a smart phone. any idea?

 

[NoTime]

You would need to find the connector pinouts for your particular device.

 

[rahul_sabnani]

what do you mean by the connector pinouts? connector pinouts of what?

 

[NoTime]

Places where you can plug things into.
For example the connector the charger plugs into usually has more than two contacts (or pins).

 

[rahul_sabnani]

ok. so what do i do with these pinouts? i mean how would you advise me to go ahead with this idea?

 

[NoTime]

Try google -> connector pinouts for (model)
Or Ask the manufacture
Or run some black box tests.

As berkeman mentioned "Sounds like a good way to hurt your phone."

 

[cristo]

What exactly is the "device" you are trying to power?

 

[rahul_sabnani]

it is a device that senses speech signals and sends it to the phone. do you have any idea about my question?

 

[berkeman]

it is a device that senses speech signals and sends it to the phone. do you have any idea about my question?

You mean a microphone? Why does it need power?

 

[cristo]

You mean a microphone? Why does it need power?

yes ... and why would you want to connect a microphone to a cell phone? If it's one of these fancy ones, then surely it can record sound

 

[rahul_sabnani]

no not a microphone. what i mean is that my device is a circuit that senses speech signal from the neck. and then i wish to send this signal onto a phone. but in order to send i need to power the device on and for that i do not wish to use an external battery due to weight problems and all. so i wish to somehow power it on using the phone itself..understand??

 

[NoTime]

While it is open to debate as to how well it works...
Most recent phones accept voice commands how is your idea different?

 

[rahul_sabnani]

well actually i can not disclose the idea behind it and as to how it is different. it is actually a confidential matter. i would appreciate if you could help me with my basic question of getting power out of the phone. sorry but i hope you understand..

 

[mgb_phys]

If you can get a circuit diagram for the connector on the bottom of the phone - the one that chargers, hands free kits, download cablesetc plugin you might be able to pull some power from it.
You are also likely to damage the phone if you need more than a few 10mA.
A small watch battery should be enough to power a throat mic.
You can probably also feed the audio signal into the phone this way as if it came from a hands free kit.
The sound from throat mikes is rather distorted - you will have to do some signal processing in the phone to make it sound normal.
If you are planning a purely muscle sensing 'silent' throat mike - these generally need more power to detect small muscle movements and need more processing.

 

[NoTime]

How did the ideas already presented work out for you?
Nobody is going to answer your original question without a model number.

You may also want to do a literature search to see if your "device" already exists.

 

[rahul_sabnani]

i made the device by myself and it is working. the only thing is that i have tried it by connecting it to the usb of the computer. and it works as the usb of computer acts as a host. but when i was trying to use the usb of the phone, it seems it would not work as the manufacturers say that the usb of the phone is not a host..so that is why me thinking of other ways

 

[rahul_sabnani]

Hey mgb_phys,
thanks for the reply. but what do you mean by feeding the audio signal as if it came from a hands free kit? how do you think that would help? can you tell me in detail. the signal processing part is not a problem.

 

[rahul_sabnani]

and i guess hands free is a passive(analog) device. it transmits a small signal when we speak and the phone amplifies it. but in my case if my device is not powered then how would the signal pass as my device is an active one?

 

[mgb_phys]

The hands free kit is at it's simplest just a microphone and headphone socket.
If you are planning to do the processing inside the phone's software then it should be failry easy to get at this audio signal. It'sunrelated to getting power out, there MIGHT be a +5v line on the connector to allow things like download cables to sense that a phone is connected, it's not guarranteed and the amount of power you can draw is limited.
You said you had tested your device connected to USB which suggests yuo are doing the ADC and digital processing in the device, in this case you need a data link to the phone. A simple phone will only be a USB peripheral and so will need a host to connect to, you mighthave mor eluck with a smart phone that can be USB host, or use bluetooth?