Wideband Lambda Probe Interface (1)

Part 1: Test exhaust oxygen levels

Published in issue 1/2012 on page 16

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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Products

Components

Resistors
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)
Capacitors
C7,C8 = 22pF (SMD0603)
C1,C2,C3,C4,C6,C9,C10,C11,C12,C13,C14,C15,
C16,C18,C19,C21,C22,C23,C24,C25,C26 = 100nF (SMD0603)
C20 = 10μF 35V (Panasonic B)
C5,C17 = 220μF 35V (Panasonic F)
Inductors
L1,L2 = 47μH (SMD1210)
Semiconductors
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)
Miscellaneous
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)