Hey, I’ve been taking a bunch of designs I made for various implants and wearables and turning them into reference designs. I made a standardized module format that can fit in a breadboard for prototyping but has castellated holes so you can surface mount it to an interconnect PCB and make proof of concept devices. If it works out for your use case you can copy the reference design onto a custom PCB. Feel free to ask any questions here.
I’ll post the template information in this introductory post so anyone can use it to make their own, and then make individual replies in this thread for each design I’ve completed. Everything is open source CC BY-SA. All the PCB source files are included for Altium Designer, but the zipped up Gerber folder in each project directory can be used to order the designs without any ECAD experience. The order instructions for PCBWay and a mechanical drawing are included in this template directory.
This reference design is for the NTAG 5 Link NTP5332 chip. It has NFC energy harvesting and a very interesting “Transparent I2C Master Channel” so that you can send commands from an NFC reader through the chip to any attached I2C device like a sensor, and it will relay the I2C response back through NFC to the reader. This means you can power and communicate with I2C devices without a microcontroller on board. Two optional sensors are on board: the TMP117 temperature sensor and the ILPS22QS pressure sensor. You’ll need to adjust the values of C1, C2, C3 for whatever NFC antenna you intend to use. You can find information about antenna tuning by reviewing some of my other threads on the forum.
This reference design is for an analog heart rate sensor (photoplethysmography) based on a design shared by https://pulsesensor.com/. It uses the APDS-9008 optical sensor and MCP6001 op-amp to detect peaks in the pulsatile waveform of your heart beat. A green LED provides the light for reflectance spectroscopy, and the output triggers an NPN transistor so you can drive small loads like the LED driver in the next post.
This reference design is for a dual LED driver circuit. They use ZXSC310E5TA boost converters to efficiently drive series LEDs from an input voltage range of 0.8V - 8V. In our application we were using it to drive strings of several flexible LED filaments in series, being supplied by supercapacitors which have much of their useable energy in the low voltage region of their discharge curve. Coupling that with the above PPG module resulted in a flashing heartrate LED device that you can see in a video below.
This reference design is for a Qi wireless charging receiver. It uses the BQ51013 chip to manage Qi 2.0 compliant power contract negotiation. You can power it from phone or wireless charging pad, and it can easily source 500mA at 5V without much heat management.
This reference design is for energy harvesting and battery management. The BQ25505 chip can handle input from a variety of energy harvesting sources like photovoltaics, thermoelectric generators, and near field RF coupling. The default configuration described in the bill of materials will configure the maximum power point tracking to 50% of VOC and allow energy harvesting from 125kHz power sources like the taidacent commercial emitters intended for lighting up dioramas with wireless LEDs. The solder jumper can allow default MPPT values of either 50% for TEGs and near field RF or 80% for photovoltaics. You can change the values of R1 and R2 to manually adjust the MPPT percentage for optimization. C3 and C4 can be changed to adjust the LC tank circuit to resonate with different antennas, or left DNP for TEGs and photovoltaics. The BAT and GND pins allow connection of a variety of energy storage solutions like lithium ion batteries and supercaps, and has power path mosfets that allow various protection features like UVLO, OVP, OCP, and different charge/discharge voltages. Resistors R3-R7 configure the IC. The output is unregulated but could be connected to an efficient buck regulator like the TPS62736. Our intended use case was trickle charging small lithium ion cells like the CG-425A through a titanium enclosure, which is possible without much heating of the enclosure because there is no foreign object detection and power contract like there would be if using Qi wireless charging.
