Project:
We have an existing sensor interface shield with schematics that utilizes Particle IoT modules as the primary logic and communications chips. However, we need to create a version of these boards for Pycom chips as well (GPy, LoPy4, FiPy)
Because Pycom boards do not have an internal battery charge circuit, fuel cell chip, on-board microusb connector, etc. like the Particle chips do, these will have to be added to our board.
This board will be used in environments from -10C to +35C and in high humidity (normally 85+%). The current design uses all automotive grade components and keeps these conditions in mind.
Existing board schematics and design files are available on github
We need to incorporate the following features into this sensor board:
1) LiPo Battery charging via solar panel (up to 6V/9W solar panel) or wall power supply (5v)
1a) Charge status LED
1b) Charge status LED should have jumper to be able to cut power to it for low power applications
1c) MicroUSB power connector
1d) Power switch to be able to kill power from battery completely without needing to disconnect battery and input power
2) MicroSD Card storage (in SD mode, not SPI mode - Pycom expects specific pins to be used
3) Fuel gauge circuit to get battery level via I2C
4) Input voltage and current monitoring (** existing schematic for INA226)
5) MicroUSB connector to communicate with the Pycom chip
6) Terminal blocks for:
6a) Analog and Digital I/O
6b) TTL Serial
6c) 3.3V, 5V, and GND pins
7) Two 4-20mA current loop circuits on terminal blocks (** existing schematic)
7a) Current loop circuits needs to be able to be disabled by I/O pin either on pycom directly or I/O expander)
8) Two Atlas Scientific EZO carrier board circuits on terminal blocks (** existing schematic)
8a) EZO circuits needs to be able to be disabled by I/O pin either on pycom directly or I/O expander)
9) On board temp/humidity/pressure sensor (** existing schematic for BME280)
10) Header pins for I2C lines
11) Need DIP switches (4-6 position) to be able to set various configuration options which will be read in by the Pycom. The pycom boards have limited I/O pins, so we will likely need I/O expander such as MCP23008 so that we can read these values in via I2C.
12) Ethernet Interface (this MAY not be needed if we can use Pycom's PoE ethernet module for the pygate. We are working with them on this now)
12a) Ethernet module should be able to be omitted from board population or disabled via a jumper if needed to save on cost/power depending on the specific application)
13) RTC chip with backup coin cell battery on-board
IF POSSIBLE (VERY nice to have):
14) USB interface for the on-board MicroSD card. We would like to be able to plug in a USB cable from a computer to a port on the board and access the microsd card as a mass storage volume from the computer. This would allow us to read/write config data and copy log files off the device without removing the card from the board. This is actually pretty important as these devices are used in the wilderness, commonly over moving water, and we have already lost a couple cards this way. Being able to just plug in a USB cable to the board to be able to mount the card on the computer as a mass storage drive would help prevent this.
As you can see, most of the sensor interfaces we already have schematics for, but we don't have the PCB design files in Eagle/Altium for the existing board. We have worked with another engineer for a couple years on this, and he is currently unavailable for the foreseeable future due to a family emergency.
The common underlying theme of the design of this board is LOW POWER. These devices are used primarily off-grid on solar/battery power only. They need to be able to last a week without solar input, which is why we need to be able to disable different areas of the board via I/O. We typically disable ALL sensors to prevent power consumption, and only turn them on for a short amount of time when we need to take a reading. So while you are designing this board, please take this into consideration.
We are VERY open to your ideas and suggestions. We love to hear input and get your thoughts. If you can think of a better way to do something, or think we are doing something stupid, please tell us! No offense will be taken! If you hate one of our existing schematics or think it can be improved, PLEASE let us know. Convince us of the improvement and we'll pay you extra to re-work that piece. Please reply with your favorite color as well so that we know you actually read this, too. We know that fixing things in the design phase will save a lot of money in the long run, so don't be shy!
If you need any more information please let me know and don't hesitate to reach out.
About the recuiterMember since May 20, 2018 Surya S
from Texas, United States