USB Data Pins
 

Alright, i have finally started an external DIY charger project that i have put off for quite sometime now.

A typical USB cable for the nano-clones has 4 pins, 2 for power supply, 2 for data in/out.

Now, i am able to supply the 5V required for the player to charge. Also, i've measured the current that goes to the player is about 160mA. All these fits a typical USB output rating.

When i connect the player to the DIY charger, the DIY charger appears to be an external battery rather than a charger.

Example, the player shows 1/3 battery life. When connected, the battery life becomes 2/3.
As compared to normal charging via computer or AC adaptor where the battery icon animates, the battery icon now does not animate.
This i assume that the external DIY charger acts as a parallel battery source now?

So the question is, what kind of input does the 2 data pins need? Logic 1 or 0? As i've left it open-circuit at the moment.
Also, is 160mA enough? It is very difficult to measure the current that supplies the player when charging via computer.

Perhaps someone with USB knowledge can answer this?

Re: USB Data Pins
 

OK, first of all you need to pull the data pins down to GND with 15k resistors. This will enable "charging mode".

Also, a standard PC USB port can supply up to 500mA (wich is the maximum for USB2.0), so 160mA is much lower and this is why is only shows 2/3 battery level.

My wall charger can supply 1A although the MP4 player should only pull 500mA and it should be current limited internally anyway so you won't be able to get it to pull, say, 5A!! However, I haven't actually measured how much mine pulls whilst charging, so I wouldn't recommend going above 1A.

Also, make sure that your charger is current limited and has plenty of protection to prevent a smoking MP4 player.

Also, for USB data, it is not standard logic levels (0, 1), rather a duplex, differential signalling method.

zetski210 , thanks for the info.

So basically the data pins both needs to be grounded for the player to reconisge as a charging signal.

Regarding the current, i'm not sure if i am able to increase it any higher. This 160mA comes directly from a LM7805 output, only wire resistance.

It very weird, but likely what you said, i'm suspecting the current is too low. But i'll try grounding the data pins and see how it goes.

If it still doesn't work out, i'm going with a boost convertor.

Re: USB Data Pins
 

Hello Mympx partners, first !Happy birthday to these great Forum.


The IC LM78XX can supply to 1AMP what means the player can "Suck" until 1AMP from Chip but if the player only need 100mA the chip deliver 100mA to player. you need limit the current by mean of a resistance only if you will not allow the 1A to player.

There is a "Light" version of LM78XX called LM78LXX what can supply to 100mA only.

when you are charging a battery you will need "monitor" the power consumptions of player, when battery is charging they spend aprox 250 mA for a normal charge, 500 mA for a fast charge and 160 mA for a slow charge then when the consumptions drop to a fews ma (aprox 60mA) the battery is full charged and the current must be limited to aprox 10mA for a "standing" charge (supply only the current used for battery's monitor circuit) for not overcharging the battery.

regards from Colombia

impeeza , thanks for the additional info..

Another reason i was thinking that perhaps the battery i used wasn't that strong enough. It's the square 9V dry cell.

Another weird thing i noticed was when it is connectted to the charger, i measured the 9V battery and about 7.4V showed on my multimeter. Fine, i thought probably the battery was going flat.
When i unplugged it, the voltage across the pins became 9.5V instead.

But anyway, i'm thinking of some ways to draw more current from the battery.

Re: USB Data Pins
 

Ja ja you get in the tricky electronic world now you are doomed :twisted:

it happened to my in the past and my teacher told me:


"remember EVERY electronic device use some amount of electrical potential (Voltage)" and the IC are not exception the LM78XX compsume aprox 2.7 Volts... so do the math.

je je je

good luck, and remember if i can help don't doubt in contact me.

Yeah it works!

i've grounded both tha data pins and now the player reconigses the charge. The battery icon is animating.

Great! Will be putting up a guide on this DIY charger soon.. :D

For get more current from battery you must use some tricks i see in somewhere get 20A :shock: from a CR2032 (3V) i see in google.

regards

impeeza , the CR2032 are button cells, and besides button cells are not readily available in every shop. Also, i'll need a boost convertor to increase the 3V to 5V.
However, i'm not sure if a single button cell would be able to charge the player for more than 1 full charge. As these button cells are about 220-230mAh.

i'll try to get the current charger working with perhaps 4xAA cells, 6V to 5V, not as much losses as compared to the 9V cell.

The current 9V cell managed to charge my nano-clone from a flat battery to around 1/3 capacity in about 15mins. So an estimated full charge would take about 45mins or so.

hello, the 80% of charge of a litium poly battery can be reach in aprox 25 mins but a full charge may take 2 hours, i really just am learning why but http://en.wikipedia.org/wiki/Lithium...olymer_battery has been helping a lot.

regards

Alright, the 9V battery is almost flat and my player only managed about 2/5 battery capacity. Perhaps it's the low capacity of the 9V cell, those cheap batteries.

Got bored while waiting for it to charge and i just finished soldering my DIY laptop cooler! :lol:
2x16cm fans! Will be doing the base tomorrow.. :D

But anyway, will be testing with other types of batteries for the charger over the next few days. Hopefully will get 1 with reasonable performance.

Re: USB Data Pins
 

The good'ol'LM7805 is an linear reg and hence very inefficient. You would get far better results from a DC-DC converter such as a switching regulator or buck converter. These will however require additional components, but will increase the lifetime of the 9V battery.

The reason for the drop in voltage when the battery is connected is that whenever you pull current from a battery, due to the electron movement, the potential will drop. As long as the voltage is above the "dropout" voltage for the regulator, the regulator will draw current and provide a stable output voltage. However, Impeeza is correct in that there is a voltage drop accross the LM7805 and this creates power loss and heat. DC-DC converters do not have this problem.

Using a series resistor to limit current is not advisable, as the resistor will drop the voltage and therefore eliminate the voltage regulation. If you want to limit the current, use a buck converter that has current limiting features. This will also improve efficiency.


Sorry for the lecture in power electronics, but it's what I do...
Oh, and Good Luck - try not to electrocute yourself by drawing 20A from a button battery :shock: