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| Add flashlight to a smartphone, will I break it? |
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| federico:
Hi everyone. :) I just bought a 8.4 inch Mediapad M5. I intend to use it as a mobile phone, I know it's huge, but I love it and I'm getting ready to do two upgrades. I'm going to add a speaker on the back cover to answer phone calls (it has no speaker because it's a tablet) and a led flashlight. Taking the current from the USB Type C output of the tablet. I have already tested the speakers, I have connected two headphone speakers and with a switch I can turn them on and off as desired, so the phone does not always detect headphones (it would no longer play audio from external speakers). Everything ok, it works well. Then I tried to connect the LED, years ago I had done it from an iPhone and it worked very well, I had taken the current from the same poles where the current entered to charge the cellphone. But here with this damn new type-C USB port I have a problem, the GND and Vbus power pins that are used to let the current in and charge the smartphone, do not give any output voltage. |O I can detect 2.66 volts only from the GND ping and the CC2. Do you think there is no way to take power from the tablet to power a small external LED? In your opinion, if I connect a LED, (which absorbs about 250Mah) connecting it to GND and CC2 as per attached drawing, do I mess up? do I damage the new tablet I just bought? :scared: Is there any way to take the current out of this tablet? Thanks to all in advance. |
| SiliconWizard:
--- Quote from: federico on June 10, 2019, 10:35:14 am ---In your opinion, if I connect a LED, (which absorbs about 250Mah) connecting it to GND and CC2 as per attached drawing, do I mess up? --- End quote --- Yes. --- Quote from: federico on June 10, 2019, 10:35:14 am ---do I damage the new tablet I just bought? :scared: --- End quote --- Probably not (but I'd still be wary), as the CC1/CC2 pins from a host can only provide little current, but they are used to configure the role of the plugged device (with pull-down resistors), not provide any significant amount of power. I wouldn't do that under any circumstances. Use VBUS and configure CC1/CC2 properly so the host knows what kind of device it is and can provide power to VBUS. (Side note: I don't know if your LED module has an integrated series resistor or constant current driver - otherwise you'll need to add one: don't connect a LED directly to VBUS!) I suggest starting there: https://www.embedded.com/print/4458380 USB-C is significantly more complicated than previous USB connections. |
| federico:
Ok, if I understand correctly, it's a big mess .. Thanks for the reply, I had not yet found such a complete text on the subject! Sorry for the delay in my reply, but I wanted to take the time to read the text carefully and translate it, (because English is not my language), now i understand how these USB Type C works, yes, they are really complicated. Language problems aside, I'm at too low a level, I had to search on goggole: pull down resistance, then I looked for: logic circuits, then I searched: impedance, then I searched: Ohm's law, then I searched: electronics for looser.. I finally searched for: chill out music, and I paused, because I was too frustrated by my incompetence. |O As always, I will look for alternative routes, so I ordered this: I checked, and it is compatible with the OTG port of my device, technically I can eliminate the motor and connect the light I think .. about that: --- Quote ---don't connect a LED directly to VBUS! --- End quote --- I have always connected the LEDs directly to the current sources, I never put the drivers, either on the old cellphone where I had made this change, or on external batteries, etc. I know I will get a shower of insults, but why do I have to use these drivers? to improve efficiency? Thanks for the help. :-+ I am very obstinate, I want to do it. :-/O |
| Audioguru:
You do not need an LED driver, instead you need an LED current limiter, maybe a power resistor. The LED datasheet will say its maximum allowed current. Your LED is mounted on a round metal that gets hot. The heat is removed by mounting the metal on a heatsink that has cooling fins in the air. |
| janoc:
--- Quote from: federico on June 16, 2019, 10:45:59 am ---I know I will get a shower of insults, but why do I have to use these drivers? to improve efficiency? --- End quote --- Yes, you are running from the battery of the device which likely has crappy battery life to begin with. So you don't want piss that little energy you have into heating some resistors. --- Quote from: federico on June 16, 2019, 10:45:59 am ---Thanks for the help. :-+ I am very obstinate, I want to do it. :-/O --- End quote --- The Power Delivery document posted above is a good start, you can actually get a small module from AliExpress (and elsewhere) that will handle that power negotiation for you. However, the mere fact that the connector is there does not mean that the device is actually capable of powering anything through it or that it can deliver significant current - usually the OTG capability is pretty limited in that regard. Tread carefully there because you could blow some USB power handling circuitry inside of the tablet. |
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