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Wideband Lambda Probe Interface (1)

Part 1: Test exhaust oxygen levels

Wideband Lambda Probe Interface (1)
The price of fuel only ever seems to go in one direction so it is important not to waste it. The use of a wideband lambda sensor to analyse the combustion gases from a vehicle engine or heating boiler will indicate how efficiently fuel is burnt. The interface to such a sensor can however be quite complex. This design marries a lambda probe interface IC with a microcontroller to produce a stand-alone lambda measurement device. Built-in self calibration gives hassle-free setup and ensures measurement accuracy.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor Members can exclusively download these files for free as part of their Membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Extra info, Update
* Interface for wideband lambda probe.
* Suitable for wide range of Lambda values.
* Digital output with RS232 interface.
* Output of lambda value and operational status.
* Fault evaluation via diagnostics register.
* Analogue output 0 to 4 V.
* Automatic calibration.
R8 = 62Ohm (SMD1206)
R10* = 82.5Ohm (SMD1206)
R2 = 100Ohm (SMD0603)
R18,R19 = 470Ohm (SMD0603)
R9,R15,R16,R20 = 1kOhm (SMD0603)
R21,R7 = 4.7kOhm (SMD0603)
R17 = 6.8kOhm (SMD0603)
R1,R3*,R6,R11,R12,R13,R24 = 10kOhm (SMD0603)
R22,R23 = 39kOhm (SMD0603)
R5,R14 = 100kOhm (SMD0603)
R4 = 470kOhm (SMD0603)
*For LSU4.9:
R3 = 31.6kOhm (SMD0603)
R10 = 300Ohm (SMD1206)
C7,C8 = 22pF (SMD0603)
C16,C18,C19,C21,C22,C23,C24,C25,C26 = 100nF (SMD0603)
C20 = 10?F 35V (Panasonic B)
C5,C17 = 220?F 35V (Panasonic F)
L1,L2 = 47?H (SMD1210)
D1 = SM6T30CA (SMB)
D2 = MBRS320 (SMC)
D4 = MURS120 (SMB)
D6 = 1N4148 (Minimelf)
LED1 = LED, red (SMD0805)
LED2 = LED, green (SMD0805)
Q2 = IRLU024N (TO251)
IC1 = Atmega8-16TQ (Atmel), programmed, Elektor #110363-41
IC2 = CJ125 (Bosch)
IC3 = 7805
IC4 = LM4041 (SOT23)
IC5 = LMV321 (SC70)
IC6 = SP3232EB (TSSOP16)
Fuse, 4A (Schurter type OMT 125 4.0A)
Fuse, 500mA (Schurter type OMT 125 0.5A)
Q1 = 14.7456MHz quartz crystal (HC49-SMD)
X1,X2,X4 = 3-way PCB terminal block, 3.5mm pitch (AKL059-03)
X3 = 8-way PCB terminal block, 3.5mm pitch (AKL059-08)
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