Blade Nano QX Charger hacking

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Blade Nano QX Charger hacking

Postby xiaoshu » Mon Nov 20, 2017 7:15 am

Yesterday I've got a Blade Nano QX micro drone that my friend send to me . It's awesome.But when I use it I meet a problem. It arrives with a USB charger for the 150mAh 1S lipo battery, that has one very annoying feature. When it's charging a red LED is on, and when it's done charging the LED turns off. Overcharging the battery will damage it, so when charging I sit by the PC (or a USB wallwart) and wait till it's done.

In the meantime I've hacked a better solution using an Arduino UNO and some passives - I've taped an LDR on the LED, and connected another LED and a small piezzo buzzer to the Arduino. Now, when the LED is on (charging) my LED is also on (so I know what state the charger is in even though electrical tape is hiding the original LED [from admin: url removed, stealth advertising detected]), and when the LED turns off my LED turns off and a short melody is played on the piezzo. This was I don't have to sit by the charger.

Before I go on and move the project to an ATTINY and create a custom 3D printed housing for everything, I wanted to ask if there's a way to cut power to the charger, so I can have it connected to USB, but stop drawing current and stop charging the battery, in a way that I can safely leave the battery plugged in but not charging anymore.

I thought about using a transistor to monitor the LED and as soon as the LED is off, connect the transistor's base to ground and have it stop providing current to the charger.

The charger only uses the vcc and gnd wires on the USB.
Several questions that I had, but don't have enough data to answer:
Is a standard p2n2222a bjt OK for this?
Is it OK to leave the battery connected to the charger even if the charger isn't connected to anything?
what sort of protection should I add to the circuit if the solution I thought of is adequate?

As far as schematics or datasheets go - I couldn't find any. The user manual for the charger has no specs (

Only info available is :

Input: DC 5V, 350mA Output: 4.2V, 300mA

I've created a (very) crude schematic .

A picture of the charger (a simple USB dongle with one LED and the eflite micro connector)
Power comes in through the male USB connector, and goes out to the charger through the female USB connector. The Transistor should stop providing power to the charger as soon as the photocell resistor detects that the charger led is off.

I currently have the circuit working WITHOUT the transistor - meaning the microcontroller and the charger get their power from separate USB ports, and I have to manually disconnect the charger when charging is done.
Thanks all guys who give advises.
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