Introduction: IOT123 - I2C MAX9812 BRICK
The IOT123 BRICKS are DIY modular units that can be mashed up with other IOT123 BRICKS, to add functionality to a node or wearable. They are based on the inch square, double-sided protoboards with interconnected through holes.
A number of these BRICKS are expected to be on multiple nodes (Master MCUs - ESP8266 or ATTINY84) on a site. The MCU needs no prior knowledge of the sensors purpose or software needs. It scans for I2C nodes then requests a property dump (sensor data) from each slave. These BRICKs supply 5.0V, 3.3V and another AUX line which is customizable.
This I2C MAX9812 BRICK dumps 3 sound sensing properties:
- audMin (0-1023) - lowest value inside the 50ms (20Hz) sample window
- audMax (0-1023) - highest value inside the 50ms (20Hz) sample window
- audDiff (0-50) - a value derived from the difference of aMin and aMax
Sound Levels using I2C are not expected to be used for continuous readings. Think machine noise levels, meeting/venue room occupancy or sound due to movement (water/friction).
The Keyes type sensor bricks will be abstracted first as they come with vitamins (extra components needed) included and are relatively cheep (I bought 37 for 10AUD). Other boards/circuits will be introduced to the I2C BRICKS.
The through-holes adjacent to the ATTINY85 have been left unused, to enable a pogo pin programmer while the DIP8 is soldered to the PCB.
A further abstraction, packaging the BRICKS in small cylinders that plug into a D1M WIFI BLOCK hub, pumping the values to a MQTT server, is being developed.
Step 1: Materials and Tools
There is a full Bill of Material and Sourcing list.
- CJMCU-9812 sensor (1)
- ATTINY85 20PU (1)
- 1" Double sided protoboard (1)
- Male Header 90º (3P, 3P)
- Male Header (2P, 2P)
- Jumper Shunt (1)
- Hookup wire (~7)
- Solder and Iron (1)
- Strong Cyanoachrylate Adhesive (1)
Step 2: Meanderings
In order to determine what supply voltage to support and the application of the sensor on an I2C bus, I ran the following scenarios. A sound test file from https://www.audiocheck.net/Audio/audiocheck.net_dynamiccheck.ogg was used. #1 & #2 sketch. #3 & #4 sketch. #5 & #6 sketches (UNO & ATTINY85). Using the Arduino IDE Serial Plotter.
- 5V VCC sensor on Standalone Arduino UNO
- 3V3 VCC sensor on Standalone Arduino UNO
- 5V VCC sensor on Standalone ATTINY85
- 3V3 VCC Sensor on Standalone ATTINY85
5V VCC sensor on I2C 5V VCC ATTINY85 Slave connected to Arduino UNO
3V3 VCC sensor on I2C 3V3 VCC ATTINY85 Slave connected to Arduino UNO
#4 for some reason took ~15 seconds to become responsive where as #6 was responsive immediately.
#1 - #4 had similar resolution as they were connected directly to the analog pin. #5 & #6 had less samples being reported as they where slowed by the I2C bus.
The conclusion was there would be a limit to the applications the I2C sensor could be used for and that 5V/3V3 will be supported.
Step 3: Prepare the ATTINY85
AttinyCore from the Boards Manager is needed. Burn bootloader "EEPROM Retained", "8mHZ Internal" (all config shown above).
The GIST can be found here:
You may find more details in these instructables:
Best to test via breadboard before continuing.
If you have existing ASSIMILATE SENSORS, make sure the slave address is different on a SENSOR/MCU Host combination i.e. all the Temperature sensors can have the same address as long as you only have one Temperature sensor on a MCU/node.
Step 4: Assemble the Circuit
- On the CJMCU-9812, attach the Electret Mic so that it is facing away from the 3 through-holes.
- On the front, insert the components ATTINY85 (1), 3P 90deg male headers (2)(3), 2P male headers (4)(5) using the glue if well ventilated, and solder off on the back.
- On the rear, trace a bare wire from SILVER1 to SILVER2 and solder.
- On the rear, trace a bare wire from SILVER3 to SILVER4 and solder.
- On the rear, trace a red wire from RED1 to RED2 and solder.
- On the rear, trace a red wire from RED3 to RED4 and solder.
- On the rear, trace a yellow wire from YELLOW1 to YELLOW2 and solder.
- On the rear, trace a blue wire from BLUE1 to BLUE2 and solder.
- On the rear, trace a green wire from GREEN1 to GREEN2 and solder.
- On the rear, trace a black wire from BLACK1 to BLACK2 and solder.
- On the rear, trace a black wire from BLACK3 to BLACK4 and solder.
The sensor can now be connected directly via its pins to the PCB or via wires, to the points shown in the pin contract.
Step 5: Testing
A number of these BRICKS are expected to be on multiple nodes (MCUs - ESP8266 or ATTINY84) in an environment. This is a unit test: checks the UNO requests/responses until all the data has been dumped, then neglects the I2C slave.
- Upload the UNO code to your UNO test harness. Ensure ADDRESS_SLAVE matches the BRICK's I2C address.
- Connect the 3.3V or 5.0V on UNO to a VCC on BRICK.
- Ensure jumper for that pin is on.
- Connect the GND on UNO to GND on BRICK.
- Connect the A5 on UNO to SCL on BRICK.
- Connect the A4 on UNO to SDA on BRICK.
- Connect a 4K7 pull-up resistor from SDA to VCC.
- Connect a 4K7 pull-up resistor from SCL to VCC.
- Connect your UNO to your Dev PC with USB.
- Open the Arduino Console.
- Choose 9600 baud (restart the UNO and reopen the console if you have to).
- The output should be printed to the console once then the word sleep is repeated.
Step 6: Next Steps
The basic layout of the circuit and the I2C layer of the software is relate-able to many different sensors. The main thing to get right to start with, is the packet contract between master and slave.
I have slated/started a (3D printed) packaged network of sensors that use this framework and will link to it as parts are published.