What is it?

You probably know the TP4056 - a classical lithium battery charging chip. However, it's parameters are not adjustable, meaning you are stuck with a charging voltage of 4.2 V and you need to change a resistor every time you want to change the chargingcurrent. This gadget allows you to very simply configure your charging profile - and not only Vmax and Imax, but also min/max temperatures, cutoff current, precharging voltage and current. So it is very good if you have many different sizes/types of lithium-based batteries (or you just want to experiment with different charging parameters).

There are a total of 8 configurable parameters:

• Vmax - maximal charging voltage, usually 4.1 to 4.35 for lithium batteries
• Imax - maximal charging current, depends on your battery & usb socket. Max 2 amps.
• Vpre - if the battery starts with a voltage below this, it is firstly precharged before switching to full-blown charging
• Ipre - current during precharge
• Icut - cutoff current at which the charging is stopped
• Tmin - minimal temperature (ignored if temperature sensor is missing)
• Tmax - maximal temperature (ignored if temperature sensor is missing)
• Vcon - on power-up, the device starts monitoring the output; if a voltage higher than this appears on the output, it starts the charging process. You can usually find these parameters in the manufacturer's datasheet for you battery.

The configuration itself is done via serial (baud 19200) - you plug this into your computer and it acts as a serial COM port and a configuration portal shows up. There you can adjust whatever you want, all changes are stored in EEPROM. You can then unplug this, plug it into a wallwart, connect a battery and it performs the charging process according to the saved parameters. It does, however, output the current charging parameters via serial, so if you have a computer with a 2 A USB socket, you can watch your charging process in real time.

The principle of operation is described in detail on my blog (see the 'documentation' link), but simply said, it's a buck converter with an ATtiny44, MCP1501 (precision 4.096 V reference) and an CH330 USB-serial. There's also a WS2812 LED for state-of-charge signalization.

Everything is open source (see documentation), so feel free to make it yourselves!

Update: I am currently sending new revision of this board (rev 1.1). Some of the updates are: - components only on one side, making it more durable (you can wrap it in heat shrink tubing, if you want - or I can do that for you for free, just send me a message). - generally improved layout, with a different MOSFET (incresed efficiency) - different voltage reference