Tricarico
Junior Member level 1
Hi guys, I'm an electronic newbie, reading some books and I thought I had finally understood the basis of circuitry, but no... I didn't. I'm a pic programmer and began on arduino a few years ago. I saw a hole in all this "arduino stuffs" that only electronics could fill so I decided to study it.
In arduino forums, what I call "5v forum" :razz: they say that you can reduce voltage using resistors and ohms law, this made my mind to fly. I made some basic circuits using only resistors and everything worked like a charm.
So I got a tablet that cannot turn on anymore - a very cheap and simple model - to fix it. I tested the battery (3.7 v) and the measures said 0 v, completely killed. I used an dc power supply at 4.2 volts to get it to life again and it worked for a while. But not enough to start the tablet, it doesn't even blinks.
The external connector seens not get any load, it's broken. So I had to made all the tests on the battery wire. I applied 4.2 v on the battery output and the tablet was on, like magic, my life turned blue again. So I decided to leave the battery and use a simple wire to an usb 5 v wall source. All I had to do was using a resistor to reduce the 5v to 4.2 and voilá! But no... again... Actually, that's where my problem begins.
Using ohms law, r = (5-4.2) / 0.8
So I have to use 1 ohm resistor to do that? Is that correct guys?
I don't have 1 ohm resistor, I don't know even if it's possible. I took a potentiometer in the lowest resistance level witch gave me 2.2 ohms. Very near I right? But no results, no response from tablet. All the tests I made here was direct on the battery wire.
I want to know your opinion about this guys, about what should I do?
Well, I don't like to give up so I read some posts in other forums, someone came with a suggestion to use 2 diodes in series. I had two diodes from an old tv (eic ba 159). Measuring the voltage between the two diodes, gave me perfect 4.2 volts! I understood the drop voltage on diodes but nothing happens. I thought my wall dc source was giving low current, it says 2A but I'm not sure if it's true (I'm in Brazil, we have many crap in here...). I tried with my dc power supply (I'm sure it can give up to 2A) and this time tablet blinks and shutdown 1 second later.
So, my big question:
Why doesn't work? An I using a wrong diode? Should I use a resistor? (when should I use resistor or not?). Did I said something wrong on my electronics learning?
I know it's a long question guys, thank you for reading.
In arduino forums, what I call "5v forum" :razz: they say that you can reduce voltage using resistors and ohms law, this made my mind to fly. I made some basic circuits using only resistors and everything worked like a charm.
So I got a tablet that cannot turn on anymore - a very cheap and simple model - to fix it. I tested the battery (3.7 v) and the measures said 0 v, completely killed. I used an dc power supply at 4.2 volts to get it to life again and it worked for a while. But not enough to start the tablet, it doesn't even blinks.
The external connector seens not get any load, it's broken. So I had to made all the tests on the battery wire. I applied 4.2 v on the battery output and the tablet was on, like magic, my life turned blue again. So I decided to leave the battery and use a simple wire to an usb 5 v wall source. All I had to do was using a resistor to reduce the 5v to 4.2 and voilá! But no... again... Actually, that's where my problem begins.
Using ohms law, r = (5-4.2) / 0.8
So I have to use 1 ohm resistor to do that? Is that correct guys?
I don't have 1 ohm resistor, I don't know even if it's possible. I took a potentiometer in the lowest resistance level witch gave me 2.2 ohms. Very near I right? But no results, no response from tablet. All the tests I made here was direct on the battery wire.
I want to know your opinion about this guys, about what should I do?
Well, I don't like to give up so I read some posts in other forums, someone came with a suggestion to use 2 diodes in series. I had two diodes from an old tv (eic ba 159). Measuring the voltage between the two diodes, gave me perfect 4.2 volts! I understood the drop voltage on diodes but nothing happens. I thought my wall dc source was giving low current, it says 2A but I'm not sure if it's true (I'm in Brazil, we have many crap in here...). I tried with my dc power supply (I'm sure it can give up to 2A) and this time tablet blinks and shutdown 1 second later.
So, my big question:
Why doesn't work? An I using a wrong diode? Should I use a resistor? (when should I use resistor or not?). Did I said something wrong on my electronics learning?
I know it's a long question guys, thank you for reading.