I use lithium polymer (LiPo) batteries very often in my projects. They are small, have very high current density, inexpensive, and rechargeable. They've become a staple in my electronics workbench. There is one problem that I have with them. They have a non-breadboard friendly connector called a JST connector. JST connectors are great for their application, but it makes interfacing the LiPo with my breadboard projects a bit difficult. I usually plug two small wires into the JST connector, then plug those wires into my breadboard, but that has not been a very neat solution for me. Eventually, I decided to make these little breadboard power supplies as a nice way to interface the battery to my breadboard projects. I love them. I would like to share my project with you all and hopefully you like them as well.
Also, I introduced the project on Adafruit Show and Tell. Check out the video at the 6:20 mark
Step 1: I Love Open Source Hardware!
I love open source hardware! As a result, I've uploaded all the Bill of Materials (BOMs) and design files for each of the designs. Please see the individual BOMs for the list of components and where to buy them.
Furthermore, the products are currently available at GroupGets for sale. So feel free to buy them or just download the BOM and design files and make your own!
You can find the GroupGets campaign here
Please find the GitHub repos for each design in the following locations or generally at: https://github.com/CalvEngIO
LiPo Battery Breadboard Power Supply: https://github.com/CalvEngIO/LiPoBatteryBreadboar...
LiPo Battery Breadboard Power Supply with Charging: https://github.com/CalvEngIO/LiPoBBSupplyWithChar...
LiPo Battery Breakout: https://github.com/CalvEngIO/LiPoBatteryBreakout....
LiPo Charger: https://github.com/CalvEngIO/LiPo-Charger.git
Step 2: Key Components
I've developed 4 different types of these power supplies with key features.
The connector mates directly with the LiPo battery. It's very snug and has two pins for "Power" and "Ground"
3.3V regulator, AP2210K
5V logic is still popular in the Maker community, but 3.3V logic is soon becoming the de-facto standard (you could probably argue that it already is in the industry). I actually find myself using 3.3V more than anything personally, usually because I always use LiPo batteries, so it made more sense to use a 3.3V regulator, as opposed to a boost circuit to get the voltage up to 5V. Also, boost circuits can induce quite a bit of switching noise on the power supply, which is usually a problem for my applications.
Battery Charger, MCP73831T
It's pretty handy to have a charger built into the board so you can charge the battery without removing it from the power supply. I decided to move this to a separate design however. It was my first time tackling these types of boards, so I went with the easiest, cleanest solution first.
Voltage Selection Jumper
3.3V does usually let me do what I need to do, but the 300mA output current limit of the regulator may be a bother for some. I added the selection jumper just in case I need higher current out and needed to power directly from the battery. I often do a lot of low power sensor circuits, so 300mA is quite fine most of the times, however. The voltage selection headers are 3 pin males headers and they are labeled with 3.3V (or VReg on one of the boards) and RAW (or LiPo on one of the boards). Connect the center pin to 3.3V if you would like to power from the regulator. Connect the center pin VRAW if you would like to power directly from the LiPo battery. I use a simple shunt (Digi-Key part number: S9337-ND) to make this connection.
I learned this from Ladyada. Always include an ON/OFF switch. So I did. This also allows me to power down the board without removing the battery. As you may know, LiPo batteries typically sit pretty snug in the JST connector, so removing them as little as possible is most ideal.
I used LEDs to indicate the current status of the board. I've gotten quite a bit of inspiration from Adafruit and SparkFun's designs over the years and learned pretty quickly how handy status LEDs are.
Step 3: Without Charging
This version breakouts the LiPo battery out to the breadboard power rails on both sides. It includes an ON/OFF switch for the regulator that can be used to power the whole board down. It also has a voltage selection jumper which enables the user to select between powering from the 3.3V regulator or directly from the LiPo battery for higher current capabilities.
Going a bit more into the ON/OFF switch, the AP2210K has an ENABLE pin (pin 3). By pulling this pin LOW (to ground), you disable the regulator. Pulling the pin HIGH (up to the supply voltage), you enable the regulator. Then, you use the voltage selection jumper to power from 3.3V or from the LiPo battery directly. The ON/OFF switch allows the circuit to go into low power mode disabling the regulator, all the LEDs, and so on. This way, you can leave the LiPo battery plugged into the breakout and conveniently flip the switch and keep working on your projects.
Pin-out from regulator's datasheet: https://www.diodes.com/assets/Datasheets/AP2210.p...
Link to GitHub repo: https://github.com/CalvEngIO/LiPoBatteryBreadboardSupply.git
Step 4: With Charging
The version with charging incorporates a MCP73831T LiPo battery charger IC. It's a very popular PMIC (power management integrated circuit) for charging LiPo batteries. SparkFun and Adafruit use it in their products, which is were I got the inspiration. It is pretty simple. You connect pin 3 (VBAT) to the LiPo battery, and input 5V into pin 4 (VDD). The chip handles all the logic for charging a battery. It charges automatically when 5V is put on pin 4, stops charging when it detects the battery is fully charged, or when 5V is removed. The breadboard power supply includes a 10.2k resistor between the pin 5 (PROG) to ground. This sets the charger for 100mA charging current which fits USB standard. This fits my favorite battery capacity size as well (400mAh from SparkFun).
On the breadboard supply, charging is enabled as soon as a micro USB cable is plugged in while the ON switch is in the "ON" position.
Link to GitHub repo: https://github.com/CalvEngIO/LiPoBBSupplyWithCharging.git
Step 5: JST to THT Breakout
And for instances where you need a simple JST to THT (through-hole) breakout, there's this. This breakout is for when I need a simple interface without all the other features of the previous supplies. This is also incredibly cheap and easy to assembly, so I can get a ton of them no problem and leave them lying around my workshop at home or at work. The four headers pins plug right into the rails of your breadboard. Only two of the pins are electrically connected to power and ground, while the other two are for mechanical stability.
Link to GitHub repo: https://github.com/CalvEngIO/LiPoBatteryBreakout.git
Step 6: Battery Charger
I buy a ton of SparkFun's LiPo chargers. My one issue is that the battery charger doesn't have adjustable charging current. Additionally, the charger is set for 500mA, which is actually a bit high for my favorite battery size (400mAh). Typically, you don't want to charge the batteries with a higher current than their rated capacity. Furthermore, I always found myself wanting a convenient breakout for the STATUS pin (pin 1) so that the charger can be embedded into other projects and a host microcontroller can monitor the charging status of the battery. As a result, I decided to make my own version to remedy a few of the concerns I just listed.
This version is set for a charging current of 100mA (fitting USB standards). I also broke out the pins of the battery charging IC (MCP73831T). This also allows the user to change to the charging current by adding a resistor from PROG to GND. This pin will be placed in parallel to the 10kiloOhm resistor built into the board, so don't forget about your equivalent resistance calculation. The charging current is given by the equation
I(charging) = 1000V / R_PROG, where R_PROG is the resistor value between the PROG pin and GND. The datasheet describes this on page 15 in section "5.1.2 CURRENT REGULATION SET (PROG)".
Link to GitHub repo: https://github.com/CalvEngIO/LiPo-Charger.git
Step 7: Remix and Share
Thanks for reading!
Please share your breadboard power supply designs! What features do you find handy?
Please feel free to take a look at the EAGLE files as well as the Bill of Materials (BOM). My next version will include a boost circuit to give a 5V output. I know quite a bit of people would find that helpful so it would be a pretty useful addition in my opinion.