EfiO2Meter General Info

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note : this is a brand new efiLabs product and we're in the process to create the documentation as well as updating our main web page at efiHacks.com ... please bare with us and give us a few days :) to complete this task while we are also cranking out the necessary tasks for mass producing this exciting efiLabs tool. production units should be available by late july ...
now late oct ... had to overcome a very tricky hw bug, an open connection on the VM signal on the sensor connector, which only shows up upon heating the sensor and then it's only detectable on the sensor side ... duh ... and we were looking at the signals on the board ... duh ... the failure signature looked like the cj125 is malfunctioning or the sensor itself.
we also switched cpus and are running it now on a arm-cortex lpc1347 ... also a 2 channel instrument is in the works..
as of now, we have 2 production style boards (pics below) running and passing all tests :)


About and more about the efiO2Meter

This page provides an overview of the efilabs bluetooth based Wireless Wide Band Air Fuel Ratio Oxygen Meter.
It uses the Bosch CJ125 wide band O2 sensor front-end processor and Bosch LSU 4.9 Wide Band Oxygen Sensors. Legacy support for the LSU 4.2 is also available.

Sensor is not Sensor, find out more about the LSU 4.9 vs LSU 4.2 sensor.

The design is based upon a 32-bit arm-cortex cpu running at 72 MHz and code written in C++ modules.
A 2nd CJ125 piggyback-daughter board has also been designed into the overall concept and should be available shortly after the basic unit is finished.
This add on option allows to measure dual exhaust systems equipped with 2 LSU 4.x sensors

This info page will also describe the instrument connectivity, the functionality of the LEDs, the sensor type and range selections and more important information on the handling of this instrument.

Do NOT, even accidentally, disconnect the sensor while the unit is powered on. Damages to the Sensor and or Instrument could occur .... that's what the Bosch documentation says.

efiO2Meter Controller Board

Top view of the efiO2Meter Instrument Circuit Board.

EfiO2Meter board top.jpg

Bottom view of the efiO2Meter Instrument Circuit Board.

EfiO2Meter board bot.jpg

Summary of the efiO2Meter Instrument Circuit Board.

Basic Measurements and Operations

The basic functionality of the Instrument is to control the wide band O2 sensor and provide the O2 Air Fuel Ratio measurement results.
The LSU 4.x sensors are complex devices and require 2 PID control loops, one fast one for the ion pump current, which is proportional with a linearizing function to the air fuel ratio and the 2nd one being a slower PID control loop to keep the sensor sensing element at a constant temperature to provide accurate readings.

Operations Environment Optimizations

To achieve a long functional sensor operations lifespan, the heating process from a cold sensor to the final operating conditions and during normal operations, the software observes the strict regulations provided by the sensor manufacturer (Bosch).
In addition a few safety mechanisms have been built into the software to guarantee a safe and long lifespan of the sensor.
To prevent drops of condense water to hit a hot sensor during an engine cold start, a variable sensor warm-up delay is available in software to assure that all water has been evaporated at the sensor location before the sensor starts with the heat-up process to reach normal operating conditions.
A sensor startup signal and a software controlled heater on / off command can also be used to accommodate customer specific operation conditions.

Measurement Data Display and Configuration

While the Instrument does not have any display, it provides 2 different channels of serial communications and software application support for the Windows, Linux and Android Operating Systems.

One of those communication channels is an implementation of a Wireless Class A Bluetooth Radio running the SPP serial data protocol on a CSR chipset and the other being a wired RS232 Serial Channel.
While the data output is transmitted simultaneously on both channels, command reception can only be received at one at the time (receive signal OR function).

This allows the Application Software the display of the O2 readings, a small real time graph and configuration options on the display surface of your android based cell phone or tablet computer.

Datalogging of all available instrument data is also available on all supported Operating Systems.

Internal CJ125 based signals are also being transmitted and can be monitored for any kind of additional diganostic information.

We also publish the communications protocol details, so that anyone has the ability to interface to the efiO2Meter with custom written software.

Serial Communications Data

The system supports 2 different types of data transfer to the host computer. Packetized Binary Data Transfer and CSV, Comma Separated Values in readable ASCII format. More details at link.

Narrow Band Sensor Simulation Output

One dedicated analog voltage output has been implemented to simulate a narrow band O2 sensor along with adjustable O2 level trigger points and output voltage levels.

A rail / rail op amp output guarantees a full output voltage swing of 0 V to 5 V with a dynamic output impedance of 0 ohm and a 100 ohm current limiting resistor.
Output Voltages below 0.5 V require a load resistance of 5 k or higher.

This Output Voltage can be linked or referenced (added) to a virtual ground sense input.

O2 Level Analog Voltage Output

A 2nd analog voltage output has been implemented to provide a linearized O2 level 0 V - 5 V output with a software variable output range and unit conversions.

A rail / rail op amp output guarantees a full output voltage swing of 0 V to 5 V with a dynamic output impedance of 0 ohm and a 100 ohm current limiting resistor.
Output Voltages below 0.5 V and above 4.5 V require a load resistance of 5 k or higher.

This Output Voltage is efiO2Meter system ground level based.

Digital Control Signals

The Instrument provides 2 digital control signals with one being a measurement and heater start / stop (on / off) input. The other one being an error condition open drain mosfet output with jumper selectable pullup resistors for 5 V and 12 V output.

Extensive Built in Diagnostic Functions

Two LEDs are provided to indicate various operational stages of the Instrument and Sensor.

The following error conditions will be detected and output over the serial data channels :

Most short and open conditions in the sensor wiring. Extreme operating environment and out of range conditions (i.e. supply voltage range).

Up to two additional LEDs are for the indication of the bluetooth radio readiness and connecting condition.

One LED indicates a blown fuse for the heater current.

Bosch LSU 4.9 vs Bosch LSU 4.2 :

We have found a very nice Techie Comparison of the LSU 4.9 vs LSU 4.2 at

We took the liberty and copied the content rather then only providing only this link to keep this info available in case the link ever fades away :)

The techie doc copy can be found at our Bosch LSU 4.9 vs LSU 4.2 page.

Another convincing example of comparison are the measured Lambda calibration reference points for each sensor, taken from the original Bosch Sensor Data Sheets.

Bosch LSU 4.9 : a total of 25 data points

0.650, 0.700, 0.750, 0.800, 0.822, 0.850, 0.900, 0.950, 0.970, 0.990, 1.003, 1.010, 1.050, 1.100, 1.132, 1.179, 1.429, 1.701, 1.990, 2.434, 3.413, 5.391, 7.506, 10.119, 30.000

Bosch LSU 4.2 : a total of 10 data points

0.700, 0.800, 0.850, 0.900, 1.009, 1.180, 1.430, 1.700, 2.420, 30.000

Note : All published design documentation is Copyright efiLabs.com and its use is without exception FOR NON COMMERCIAL PURPOSE ONLY. For commercial licenses contact efilabs.com ... try us, we're reasonable :)

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