Difference between revisions of "CO2MeterHacking"
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Revision as of 23:44, 25 March 2014
This project is about hacking the Voltcraft CO-100 CO2-sensor, such that we can read the exact ppm value as displayed on the LCD.
This particular CO2-sensor is present in the klusbunker at RevSpace and is currently used to control the ventilation in a crude manner (by monitoring the warning LEDs on the display module). Having the CO2 ppm value available as a number allows for nice things such as logging the levels over time, announce them on IRC, show them on the LedBanner , etc.
The user manual of the Voltcraft CO-100 says "Attention! The RJ45 connection (see chapter 7, item „K“) must not be used. The connection is only intended for the manufacturer". Of course, a claim like that can only be interpreted as a challenge! :)
Investigation & findings
The CO2 sensor inside the CO-100 (in the left of the picture) has a sticker saying ZGw063RY. Googling for this number reveals a CO2 module that looks just like the Voltcraft CO-100, so it appears that the CO-100 is basically just a rebranded ZyAura ZGw063RY module.
The CO-100 seems to miss a bunch of components that can be mounted on the PCB, close to the RJ45 connection (most likely an RS232 chip with charge pump capacitors).
The CO2 sensor in the CO-100 is a ZyAura ZG-01 module. This sensor uses the ZyAura protocol, which vaguely resembles SPI, see File:ZyAura CO2 Monitor Carbon Dioxide ZG01 Module english manual-1.pdf.
On the bottom left of the PCB is a set of pads that are marked with G, C, D, V, meaning Ground, Clock, Data, Voltage of the ZG01 sensor. The voltage level on these pins is 3.3V.
The ZG-01 sends 5-byte frames containing measurement values:
- byte 0 is an identifier for the measurement item, e.g. whether it is a CO2 ppm value or a temperature.
- byte 1 and 2 contain the value of the item (byte 1 is the MSB, byte 2 is the LSB)
- byte 2 is a checksum over bytes 0-2, just the sum modulo 256.
- byte 3 is always 0x0D
Besides the CO2 ppm value and temperature, it also sends various other (so far unknown) measurement items.
Measurement items encountered so far:
|0x42 'B'||4708||Temperature in hexi-degrees Kelvin|
|0x50 'P'||857||CO2 ppm value|
|0x52 'R'||10438||Barometric pressure?|
|0x56 'V'||10443||Barometric pressure?|
|0x6D 'm'||2559||Seems to always have same value|
|0x71 'q'||855||Always close to value of item 0x50|
Software has been written to interface an arduino to the clock and data lines of the ZG-01. It consists of an finite state machine (FSM) that processes the data line on each falling edge of the clock line. The FSM assumes that a new frame is starting when the time between bits is more than 3 milliseconds. Measurements of the CO2 ppm level are sent over the air using a 2.4 GHz NRF24L01+ module.
Arduino pin mapping:
- digital pin 2 (PD2): ZG01 clock signal
- digital pin 3 (PD3): ZG01 data signal
- TODO: pin mapping of the NRF24L01+ module.
The source code can be found on github.
The plan to integrate the CO2 sensor into the space infrastructure is as follows:
- Attach an arduino to the G, C, D, V lines. The arduino takes power from the V-line and decodes the SPI-like signals from the ZG-01 on the C-line and D-line.
- Connect an NRF24L01+ module to the arduino SPI port and send the CO2/temperature frames over the air to a central NRF24L01+ receiver (e.g. the one which handles the SkipButton, Nomz Bell). The unique 4-character id for the CO2 sensor is "CO_2".
- From there on, the CO2/temperature data can be further processed (to be logged, sent to the ledbanner, announced on IRC, etc.)
This requires only minimal modifications to the CO-100 modules itself and makes uses of the existing wireless infrastructure.
- consider powering the Arduino from the 3.3V line coming from the CO2 sensor
- fix the wireless RF24 based protocol, it seems to work sometimes, but not all the time
- investigate further into the unknown measurement items sent by the ZG01