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By JOHN CLARKE Using a wideband O2 sensor in your car, Pt.2 Construction and installation details Last month, we introduced our new Wideband Oxygen Sensor Controller and described the circuit. This month, we show you how to build it and give the test and installation details. B UILDING THE Wideband Controller is straightforward. All the parts, except for the wideband oxygen sensor, are mounted on a PC board coded 05110091 and measuring 112 x 87mm. This is housed in a diecast box measuring 119 x 94 x 34mm. An 8-pin circular multi-pole panel plug connector is used to provide the interface to the external wideband sensor. This sensor is mounted on the exhaust (either directly or via an adaptor pipe) and connects to the controller via a 7-way extension cable. In addition, the controller is fed with power via leads which enter via a cable gland and these wires terminate into an on-board screw terminal block. The 3-wire connection to the optional 72  Silicon Chip Wideband Display Unit also passes through this cable gland. Refer to Fig.13 for the parts layout on the PC board. Begin by checking the board for any defects such as shorted tracks or breaks in the copper. Check that the corners have been shaped to clear the internal corner pillars of the box by test fitting it in place. Similarly, check that the board has had rectangular sections removed from either side so that it will later clear the nuts used to secure the multi-pole connector and the cable gland. The shape required is indicated using thin tracks on the underside of the PC board. Now start the parts assembly. Insert the wire links and resistors first, tak- ing care to place each in its correct place. Table 1 shows the resistor colour codes but you should also check each one using a digital multimeter before soldering it in place. The 0.1Ω 5W resistor runs cold and can be mounted flush against the PC board. Next, install the diodes, zener diodes and the ICs but don’t install IC1 (the PIC micro). Instead, install a socket at its location. Make sure that this socket and the other ICs are all oriented correctly (ie, notched ends towards the top of the PC board). Follow with the capacitors, taking care to install the electrolytic types with the polarity indicated. That done, install REG1, REG2 and Q1. These parts are all mounted flat against the siliconchip.com.au IC4 100k 22pF 82k 12k TP5 62 22k VR5 Rcal 560k Vs/Ip Vs Ip 22k IC5 1nF 10 F 560k 4148 D4 Q3 4148 100 F 4148 Q2 0.1  5W D3 LED2 D2 220nF 22k TP3 3.3nF 100 F LED1 TP8 6482AIN 4.7k 470k IC3 4052B 6482AIN IC2 LMC6484AIN VR4 100k 100k 100nF 2.2k Q1 IRF540N 100nF TP6 4.7k 10 220nF TP7 TP 5V 100k 100nF 10 F TP GND 2.2k H– 10k VR1 GND2 JP1 20k H+ 100nF TP0 TP1 100nF +12V TP4 2.2k IC1 PIC16F88-I/P VR2 1 9 0 0 1 1 5OUT 0 WIDEBAND 150 220nF 220nF TP2 1k 4004 S-CURVE OUT 470k 120 D1 150 10k 150 22 F 10 F 10 F 470 470 10 100 F GND1 100nF REG2 7808 10nF REG1 LM317T 100 F 16V ZD1 VR3 RELL ORT N O C D NA BEDI W 100 F Fig.13: install the parts on the PC board as shown here. Use PC stakes at all the test points (TP0-TP8) and make sure that the semiconductors and electrolytic capacitors are all oriented correctly. correct part at each location. Transistors Q2 and Q3 can go in next. Be sure to use a BC327 for Q2 and a BC337 for Q3. Do not get these two transistors mixed up. Once they are in, install the 2-way pin header for JP1, then install PC stakes at the external wiring positions (see Fig.14). LEDs 1 & 2 are next on the list. These must be installed with the top of each LED exactly 24mm above the PC board. You can set their height by pushing each LED down onto a 19mm cardboard spacer that’s slid between its leads. In each case, the anode (longer lead) must go towards the top of the PC board. The three trimpots (VR1-VR4) can now go in. Be sure to use the correct value at each location and orient each one with its adjusting screw as shown on Fig.13 (this ensures that the voltages at their wipers increase with clockwise rotation). Note that these trimpots may be marked with a code other than the actual resistance value in ohms, ie, the 500Ω trimpot may be coded as 501, the 5kΩ trimpots may be coded as 502 and the 1kΩ trimpot may be coded as 102. Finally complete the PC board assembly by installing the 3-way & 2-way screw terminal blocks. These must be dovetailed together to form a 5-way block before installing them on the PC board. Make sure that the wiring access holes face towards the edge of the PC board. Boxing it up The completed PC board is mounted inside a diecast metal case on plastic stand-offs. PC board, so you will have to bend their leads down through 90° to get them to fit. This involves bending the two outer leads of each device down about 8mm from its body, while the inner lead is bent down about 6mm away. siliconchip.com.au Secure the metal tabs of these devices to the board using an M3 x 6mm screw & nut before soldering their leads to the PC board. Don’t solder the leads first, otherwise you could crack the PC board pattern as the screw is tightened down. Be sure to install the The PC board is mounted inside the case on M3 x 6mm tapped Nylon spacers and secured using M3 x 4mm screws. Before doing this though, you will need to drill all the necessary holes. First, position the PC board inside the base and use it as a template to mark out its four corner mounting holes. That done, remove the board and drill these holes to 3mm diameter. Deburr them using an oversize drill. Next, you need to drill holes in the ends of the box to accept the cable gland and the 8-pin circular connector (see photo). The location and diameters of these holes is indicated on Fig.14. They are best made by using a small pilot drill to begin with, then carefully enlarging each to its correct size using a tapered reamer. October 2009  73 TO CHASSIS NEAR BATTERY –VE CONNECTION (GREEN) OPTIONAL WIDEBAND DISPLAY WIRING +12V (IGNITION) (F1) INLINE FUSEHOLDER RELL ORT N O C D NA BEDI W 12 S-CURVE OUT 1 9 0 9 0 1 5OUT 0 WIDEBAND 22 (GREEN) (GREEN) CABLE GLAND (12mm DIA) Rcal +12V Rcal (GREEN) H+ GND1 7.5A WIRE Vs/Ip (YELLOW) Vs/Ip (RED) Ip (RED) TP GND GND2 Vs Ip H– 3 4 5 8 6 1 7 (ALL DIMENSIONS IN MILLIMETRES) Vs 4148 4148 4148 2 22 (RED) HEATSHRINK SLEEVE ON SHIELD WIRES (BLACK) H+ (RED) 12 H– (BLUE) Fig.14: follow this diagram to complete the external wiring. Also shown are the locations and hole sizes for the cable gland, the circular panel connector and the earth screw. Finally, you will need to drill a 3mm hole in the front side of the case to anchor the earth solder lug. Once all the holes have been drilled, secure the board in position, then run the wiring as shown in Fig.14. Note that you must use 7.5A rated wire as marked on the diagram for the 12V supply, ground and heater wires, since these carry heavy currents. The 8-pole circular panel connector is wired by first connecting the sensor wires to the PC stakes on the PC board and the heater wires to the screw terminal block. The wires are then fed through the nut and washer for the circular connector and then through the mounting hole before soldering them to the connector itself. Note that each soldered pin is covered with heatshrink tubing to avoid shorts and to prevent the wires from breaking. This means you will have to slide a length of heatshrink over each wire before soldering it to the connector. After soldering, the heatshrink is pushed over the connection and shrunk down with a hot-air gun. Similarly, the leads for the power supply should be fed through the cable 74  Silicon Chip 25mm SOLDER LUG gland before connecting them to the screw terminal block. If you are using the wideband and S-curve outputs, these wires also go through the gland. For the Wideband Display Unit, the 0V rail can be obtained from the TP GND pin, while the +12V supply can be picked up from the +12V terminal on the 5-way terminal block. Note that the +12V supply lead requires an in-line fuseholder and 5A fuse. This supply is obtained from the vehicle’s ignition circuit. Note that, because of the currents involved in the heater circuit, two earth wires must be used as shown in Fig.14. These connect together at the vehicle’s chassis. For temporary use, the cigarette lighter socket can be used to provide power via a lighter plug connector. Sensor extension cable The sensor extension cable is wired as shown in Fig.15. Make sure that the wiring is correct and use heavy-duty cable for the H+ and H- leads. The wiring is shown from the back of each connector, so be sure to follow this carefully. Note that the 6-pin connector includes wire-sealing glands 6mm REAR OF 8-PIN MALE EARTH SHIELD CIRCULAR (GREEN) PANEL CONNECTOR (16mm DIA) and these are placed over each lead before it is attached to the 2.8mm female crimp spade terminals. That completes the assembly. Now for the setting-up procedure. Setting up & testing It’s best to initially configure the Wideband Controller to measure the oxygen content of the air. That way, the controller can be tested with a known gas, ie, one that comprises 20.9% oxygen in fresh air. This test requires the installation of two extra 560kΩ resistors in parallel with the 560kΩ resistors associated with IC5b (ie, one across the existing resistor to pin 5 and the other added across the existing resistor between pins 6 & 7). The Vs/Ip and offset voltage set by VR4 is also different compared to the normal set-up for measuring exhaust gas. If you prefer to skip the above step in the setting-up procedure, leave the extra resistors out and simply connect your multimeter between TP3 and Rcal. Set the meter to read ohms and adjust trimpot VR5 for a reading of 311Ω. That done, skip directly to siliconchip.com.au Above: this view shows the completed extension cable with the sensor attached. Vs/Ip H– (BLUE* ) (YELLOW) Vs H+ (GREY) (RED* ) 5 4 3 82 6 7 1 SHIELD WIRE Ip (RED) Vs (GREY) Rcal Rcal (GREEN) (GREEN) 8-PIN CIRCULAR LINE CONNECTOR (REAR VIEW) * H– AND H+ WIRES SHOULD BE CAPABLE OF CARRYING 7.5A Vs/Ip H+ (YELLOW) (RED* ) H– (BLUE* ) 1 3 5 2 4 6 Ip (RED) 6-PIN FEMALE CONNECTOR (REAR VIEW) Fig.15: the wiring details for the sensor extension cable. Make sure that the wiring is correct, otherwise the sensor could be damaged. Be sure also to use heavy-duty cable for the heater H+ and H- leads and note that the 6-pin female connector at right is shown from the rear. the “Engine exhaust readings setup” procedure and ignore the instruction to remove the 560kΩ resistors between TP0 & TP5 and between TP6 & TP7. Oxygen concentration settings If you do intend to first measure the oxygen content of the air, just follow this step-by-step procedure: Step 1: solder one 560kΩ resistor between TP0 and TP5 and a second 560kΩ resistor between TP6 and TP7. Step 2: remove the jumper plug from J1 and connect a multimeter between TP3 and Rcal. Set the multimeter to read ohms. Step 3: adjust VR5 for a reading of 311Ω. siliconchip.com.au This view shows female 6-pin connector (left) at the end of the extension cable and the matching male plug that comes fitted to the sensor (right). October 2009  75 (VERTICAL PLANE) Mounting The Oxygen Sensor 25 10.5 +/-0.35 3 > 10° 23 ALL DIMENSIONS IN MILLIMETRES (HORIZONTAL PLANE) Fig.16: the Bosch wideband sensor must be fitted to the exhaust pipe at an angle of at least 10° above horizontal. This is necessary to ensure that any condensation drains out during the cold starting phase. Step 4: check that IC1 is still out of its socket and that the sensor is unplugged, then apply power (12V) to the circuit. Monitor the voltage between TP 5V and TP GND and adjust VR1 for a reading of 5.00V. Step 5: monitor the voltage between Vs/Ip and TP GND and adjust VR3 for a reading of 2.00V. Step 6: monitor the voltage between TP4 and TP GND and adjust VR4 for a reading of 2.343V. Step 7: switch off and install IC1 in its socket (watch its orientation). Reapply power and check that pin 8 of IC4 is at about 8V and that TP8 is at about -2.5V. If the latter voltage is positive, check the orientation of diodes D2-D4 and check the placement of Q2 & Q3. Check the orientation of the 10µF and 100µF capacitors as well. Step 8: now you are ready to test the operation with the oxygen sensor connected. Switch off and connect the sensor to the Wideband Controller. Before switching on, check that there is resistance between H+ and H-. It should be about 3.2Ω at 20°C. Note that the sensor will get hot and so the plastic protective cap should be removed and the sensor placed on a surface that can withstand 200°C. Glass cookware (eg, Pyrex) is ideal. Note also that the tip of the heater can become very hot. Step 9: apply power and check that the Heat LED (LED1, red) lights. If is doesn’t, check its orientation. Check that both the Wideband output and the S-curve output are at 0V. After about 20-seconds, the Heat LED should start flashing and the Data LED should light. The flashing Heat LED indicates that the sensor How To Remove The Narrowband Sensor It is highly unlikely that an open-ended 22mm spanner will be sufficient to remove the original oxygen sensor. Instead, it will be so tight that the nut will refuse to budge and will simply start to “round off” under the spanner. Basically, you will require a special oxygen sensor removal tool. This comprises a 22mm socket that has a slit along one side to allow for the oxygen sensor wires to protrude. Even with this tool, we found that the oxygen sensor was difficult to remove. Initially, no amount of force would budge it as it was seized solidly in place. In the end, we used “Loctite Freeze & Release Lubricant” (Part No. FAR IDH1024403) to help free it. This “shock cools” and penetrates and lubricates the screw threads and this allowed us to eventually remove the sensor. Note that special high-temperature grease must be used on the screw threads if you refit the existing sensor. A new sensor (such as the Bosch wideband sensor) will be supplied with this grease already applied to the thread. 76  Silicon Chip TAPPED WITH M18 x 1.5 THREAD Fig.17: this diagram shows the dimensions of the threaded boss that’s used to attach the sensor. It must be made of stainless steel and should cover the sensor’s thread completely. The tightening torque is from 40-60 Nm. has reached operating temperature, while the lit Data LED indicates that the Wideband Controller is measuring the oxygen content in the air and that the reading is available at the wideband output. The wideband output voltage will be proportional to the oxygen content. A 2.09V reading corresponds to 20.9%. Step 10: check that the voltage at the wideband output is close to 2.09V. It should be within 1% of this value if you are at sea level and the measured air is not in a confined space. At higher altitudes, the value will be lower because the lower air pressure affects the reading. In practice, the air pressure drops by approximately 10hPa for every 100m above sea level, starting from a standard pressure of 1013.25hPa. However, this pressure decrease rate does not apply for altitudes above 2000m where the rate becomes non-linear. And, of course, weather conditions also affect air pressure. For more detail, refer to the Ip versus Pressure graph (Fig.11) published last month. Typically, the reading will be 4% less at an altitude of 1000m above sea level. Since the oxygen concentration versus Ip current is almost linear, the graph can also be interpreted as the change in oxygen concentration reading with pressure. The oxygen concentration in percent is the reading from the Wideband Controller. Step 11: if the reading is nowhere near the expected value, check the resistor values on the PC board. Although adjusting the value of the 62Ω resistor can recalibrate the reading, this should not siliconchip.com.au be necessary and we have not provided for trimming this resistor. Step 12: this step adjusts trimpot VR5 to give the best operating conditions for the Wideband Controller and to obtain the highest resolution available. To do this, measure the voltage at TP3 and adjust VR5 so that the voltage is at about 4.8V. This setting now suits the particular sensor connected. If you change the sensor, this adjustment will have to be repeated. Alternatively, you can just leave VR5 set at 311Ω to suit all LSU4.2 sensors. Step 13: check the various operating voltages The voltage between Vs and TP GND should be 2.450V, while the voltage between Vs/Ip and Vs should be 450mV. The voltage between TP1 and TP GND should be 2.5V. There may be small variations here as the controller continually adjusts the current to maintain these voltages. If you have an oscilloscope, you will be able to see the 177mVp-p square wave imposed on the Vs voltage used for sensor impedance measurement. Engine exhaust readings set-up Having checked that the Wideband Controller accurately measures the O2 content in air, you now have to re­adjust it to give accurate engine exhaust measurements. Here’s what to do: Step 1: switch off and remove the extra 560kΩ resistors between TP0 & TP5 and between TP6 & TP7. Step 2: disconnect the sensor, then reapply power and adjust VR3 for a reading of 3.30V between the Vs/Ip terminal & TP GND. Step 3: adjust VR4 for a reading of 3.92V between TP4 and TP GND, then check the voltage on TP1. This should be 0.385V with the sensor disconnected. This voltage can be adjusted by tweaking VR4 but the TP4 reading should still be at or very close to 3.92V. Step 4: disconnect power and reconnect the sensor. Apply power again and check that the Heat LED is fully lit. Once this LED flashes, the Data LED will also flash at the same rate, indicating that the gas under measurement (air) is too lean for the lambda range of up to 1.84 (air has a lambda of 207). Step 5: check that the wideband output is close to 5V and that the S-curve output is close to 0V. Step 6: fit jumper JP1 to the 2-pin header. The Wideband Controller is now ready to measure exhaust gas. A Bosch LSU4.2 wideband sensor is used with the Wideband Controller. Note that other wideband sensors are not suitable for use with this controller. the exhaust manifold of a turbocharged engine. Instead, it must be installed after the turbocharger. (2) The exhaust pipe section prior to the sensor should not contain any pockets, projections, protrusions, edges or flex-tubes etc, to avoid the accumulation of condensation water. Locating the sensor on a “downhill slope” of the pipe is recommended. (3) Make sure that the front hole of the sensor’s double protection tube does not point directly into the exhaust gas stream. Instead, mount the sensor Sensor installation As mentioned in Pt.1, the Bosch LSU4.2 wideband sensor can be installed in the exhaust pipe using a suitable threaded boss. This should be as close to the engine as possible. Note, however, that the exhaust gas temperature under all engine-operating conditions at the sensor position must be less than 850°C. In general, installing the wideband sensor in the same position as the existing narrowband sensor will be OK. The following points should also be taken into consideration: (1) The sensor must not be mounted in Table 2: Capacitor Codes Value 220nF 100nF 10nF 3.3nF 1nF 22pF µF Value IEC Code 0.22µF 220n 0.1µF 100n .01µF 10n .0033µF 3n3 .001µF 1n0 NA 22p EIA Code 224 104 103 332 102 22 Table 1: Resistor Colour Codes o o o o o o o o o o o o o o o o o siliconchip.com.au No.   4   2   4   1   3   1   1   2   2   3   1   2   3   1   1   2 Value 560kΩ 470kΩ 100kΩ 82kΩ 22kΩ 20kΩ 12kΩ 10kΩ 4.7kΩ 2.2kΩ 1kΩ 470Ω 150Ω 120Ω 62Ω 10Ω 4-Band Code (1%) green blue yellow brown yellow violet yellow brown brown black yellow brown grey red orange brown red red orange brown red black orange brown brown red orange brown brown black orange brown yellow violet red brown red red red brown brown black red brown yellow violet brown brown brown green brown brown brown red brown brown blue red black brown brown black black brown 5-Band Code (1%) green blue black orange brown yellow violet black orange brown brown black black orange brown grey red black red brown red red black red brown red black black red brown brown red black red brown brown black black red brown yellow violet black brown brown red red black brown brown brown black black brown brown yellow violet black black brown brown green black black brown brown red black black brown blue red black gold brown brown black black gold brown October 2009  77 Tailpipe Sensing EXHAUST TAILPIPE SENSOR CLAMP FOR ATTACHING TO EXHAUST PIPE Fig.18: follow this diagram to build the tailpipe sensor unit if you don’t want a permanent installation. MOUNTING BOSS EXHAUST OUT EXHAUST FLOW 150 100 ALL DIMENSIONS IN MILLIMETRES I F YOU DON’T WISH to install the wideband sensor permanently, an alternative is to mount it in a tailpipe extension. This tailpipe extension can then be slid over the end of the tailpipe and clamped in position – see Fig.18. Note, however, that any readings obtained using this method will be affected by the catalytic converter and so won’t be as accurate. That’s because the catalytic converter reacts with the exhaust gas and perpendicular to the exhaust stream so that it can constantly monitor fresh exhaust gas. (4) Never switch on the sensor heating until the engine starts. This means that jumper J1 must be installed to ensure heating does not begin until 13V has been measured on the battery supply. Check that this jumper is installed. 250mm LENGTH OF 38mm (1.5") PIPE changes the oxygen content. In addition, some catalytic converters include an air bleed to feed oxygen into the exhaust to allow full catalytic operation with rich gases. Of course, this won’t be a problem in older cars that don’t have a catalytic converter. However, the sensor must be placed so that the exhaust is not diluted by air. Note also that exposing the sensor’s leads to exhaust gas may alter the reference air composition of the sensor and (5) The sensor must be mounted so that it is inclined at least 10° from horizontal (electrical connection upwards) – see Fig.16. This is necessary to prevent liquid collecting between the sensor housing and the element during the cold start phase. (6) The sensor receives reference air through the connection cable. For this The Wideband Controller mates with the Wideband Oxygen Sensor Display unit described in the November 2008 issue. 78  Silicon Chip give false readings. Fig.18 should be followed quite closely if you intend mounting the sensor in a tailpipe extension. By using the dimensions shown, the sampled exhaust gas is taken sufficiently upstream from the end of the tailpipe to prevent dilution with outside air. The pipe and clamp materials can be made of steel or brass but use a stainless-steel boss for mounting the sensor. reason, DO NOT use cleaning fluids or grease at the sensor plug connection. (7) The recommended material to use for the threaded boss in the exhaust pipe is temperature-resistant stainless steel to the following standards: DIN 174401.4301 or 1.4303, SAE 30304 or 30305 (US). Fig.17 shows the thread boss dimensions. Note that the sensor thread must be covered completely. (8) The use of high-temperatureresistant grease on the screw-in thread of the boss is recommended. The tightening torque is from 40-60 Nm. (9) The sensor must be protected if an underseal such as wax or tar or spray oil is applied to the vehicle. (10) The sensor must not be exposed to strong mechanical shocks (eg, during installation). If it is, the element could crack without visible damage to the housing. (11) Both the sensor and its connecting cable should be positioned to avoid damage due to stones or other debris thrown up by the wheels. siliconchip.com.au Frequently Asked Questions Q: Can a wideband sensor directly replace a narrowband sensor? A: No, a wideband sensor must be used in conjunction with a Wideband Controller. If the Wideband Controller has a simulated narrowband output, then this scan usually be connected to the ECU’s oxygen sensor input instead of the narrowband sensor. Q: I have heard that narrowband oxygen sensor (S-curve) simulators are not recognised as a valid sensor by the ECU which records a diagnostics fault code. Will the narrowband output of the Wideband Controller be recognised correctly as a valid sensor? A: Yes, usually it will. Narrowband sensor simulators usually comprise an oscillator that delivers a voltage centred about 450mV, with a sinusoidal variation of about 50mV above and below 450mV. However, these simulators oscillate continuously regardless of mixture and do not respond in the usual manner to mixture changes (ie, where a rich mixture cause the sensor output to rise above the 450mV stoichiometric point and a lean mixture cause it to fall below this point). By contrast, the Wideband Controller’s S-curve output simulates the response of a narrowband sensor and it bases its output voltage on the actual mixture readings. So a lean mixture will cause the nar- (12) Do not expose the sensor to water drips from the air-conditioner or from sources such as windscreen run-off during rain or when using the windscreen washer. The resulting thermal stress could damage of the sensor. Fast preheat Provided the sensor is correctly installed in the exhaust pipe and is rapidly heated by the exhaust, it can be preheated more quickly by starting at a higher effective heater voltage. To do this, the code for the Wideband Controller requires a small change. This as at line 706 and involves removing the semicolon (;) from the beginning of line 706 – ie, from in front of “btfsc PORTB,0”. The file then needs to be saved, reassembled and used to reprogram the PIC micro (IC1). This change is only recommended siliconchip.com.au rowband output to fall and a rich mixture will cause the narrowband output to rise above the 450mV stoichiometric point. Consequent­ ly, the ECU will recognise the signal as valid because it responds to mixture variations correctly. Q: Can I use a different wideband sensor with the SILICON CHIP Wideband Controller? A: No, only the Bosch LSU4.2 is suitable. Q: When the wideband sensor is installed in the exhaust pipe are there any special precautions to prevent sensor damage? A: Yes. First, the controller must not be switched on until after the engine has started in order to remove any condensation within the sensor before it is electrically heated. In addition, the sensor must be mounted more than 10° from horizontal to allow moisture to run out. The sensor must also be installed where the exhaust gas heats the sensor quickly but where it does not go above 850°C. Q: Can a wideband sensor be left installed in the exhaust pipe without a controller? A: Yes, but only for a short duration. Otherwise you should remove the unused sensor and plug the exhaust hole if the sensor is not connected to a controller. Q: Can the sensor and controller be used with a 24V supply? if all mounting requirements are met. In addition, jumper J1 will need to be installed for the fast start preheat to take effect. The Wideband Controller assumes an initial temperature of -40°C for pre-heating. This ensures that the sensor is not heated too rapidly for any initial temperature that’s likely to be encountered. Using the S-curve output As mentioned, the S-curve output from the Wideband Controller can be used to replace the existing narrowband signal. However, the vehicle must be currently using a zirconia-type narrowband oxygen sensor. If the vehicle already has a wideband sensor, then this sensor should not be replaced with the S-curve signal. A less common type of narrowband A: No, the sensor is not been designed to cater for 24V operation and using it at this voltage would result in excessive heater element current. Q: Can the sensor run from a 9V (216) battery? A: No, the heater current is too high for a 216 type 9V battery. Also a 9V supply not may be sufficient for the heater to reach the required operating temperature. Q: I want to monitor the Heat and Data LEDs inside the car. Can these LEDs be external to the wideband controller and connected to the controller using long wires? A: Yes. Q: If I unplug or plug-in the wideband sensor to the controller while the controller is still powered will it damage the sensor? A: There is a possibility the sensor will be damaged, due to reverse Ip current. It’s also possible that the ceramic material may crack due to incorrect heating up from cold. Q: What is the life of the sensor? A: Typically 10,000 hours or 160,000km if handled and installed correctly. Q: How long after the controller is switched on before the air/fuel readings are available? A: Less than 22 seconds with a 20°C gas temperature. lambda sensor has a ceramic element made of titanium dioxide. This type does not generate a voltage but instead changes its resistance according to the oxygen concentration. Once again, this type cannot be simulated using the S-curve signal. Identifying the sensor leads In order replace the existing sensor with the S-curve output from the Wideband Controller, you first need to identify the leads running from the sensor to the ECU. Basically, there are four narrowband sensor variations: (1) If the sensor has one lead this will be the signal wire and the sensor body will be ground. (2) If the sensor has two leads, one will be the signal lead and the other will either be a +12V heater supply or the October 2009  79 Parts List For The WideBand Controller 1 diecast metal box, 119 x 94 x 34mm (Jaycar Cat HB-5067) 1 PC board, code 05110091, 112 x 87mm 1 8-pin circular multi-pole panel plug connector (microphone type) 1 3AG in-line fuse holder 1 5A 3AG fuse (F1) 1 DIP18 IC socket 1 2-way PC mount screw terminals (5.04mm spacing) 1 3-way PC mount screw terminals (5.04mm spacing) 12 M3 x 4mm screws 4 M3 nuts 4 M3 x 6mm tapped Nylon spacers (do not use metal types) 1 3-6.5mm cable gland 17 PC stakes 1 2-way pin header with 2.54mm spacing 1 jumper for pin header 1 solder lug 1 50mm length of yellow medium duty (2A) hookup wire 1 50mm length of red medium duty (2A) hookup wire 1 50mm length of black medium duty (2A) hookup wire 1 100mm length of green medium duty (2A) hookup wire 1 150mm length of light blue heavy duty (7.5A) hookup wire 1 4m length of green heavy duty signal common. For a heated sensor, the body will be a common ground for both the signal and heater circuits. (3) A 3-wire sensor has Heater+ (H+), Heater- (H-) and sensor signal leads, with the body as the signal ground. (4) The 4-wire sensor is similar to the 3-wire sensor but with an extra ground lead for the signal ground. In each case, the leads are quite easy to identify but first a word of warning. Do not measure the narrowband sensor impedance with a multimeter. The reason for this is that the current produced by the meter for resistance measurements will damage the sensor. Note also that the maximum loading for the sensor is ±1µA. This means that to measure the voltage produced by a narrowband sensor, the meter must have an input impedance higher than 80  Silicon Chip (7.5A) hookup wire 1 2m length of red heavy duty (7.5A) hookup wire 1 250mm length of 0.7mm tinned copper wire (or 9 zero ohm links) 1 140mm length of 3mm heatshrink tubing (or 20mm yellow, 40mm red, 40mm black, 40mm green) Semiconductors 1 PIC16F88-I/P microcontroller programmed with 0511009A (IC1) 1 LMC6484AIN quad CMOS op amp (IC2) 1 CD4052BCN 1-to-4 CMOS analog multiplexer (IC3) 2 LMC6482AIN dual CMOS op amps (IC4,IC5) 1 LM317T adjustable regulator (REG1) 1 7808 8V regulator (REG2) 1 IRF540N 100V 33A N channel Mosfet (Q1) 1 BC327 PNP transistor (Q2) 1 BC337 NPN transistor (Q3) 2 3mm red LEDs (LED1,LED2) 1 16V 1W zener diode (ZD1) 1 1N4004 1A diode (D1) 3 1N4148 switching diodes (D2-D4) Capacitors 5 100µF 16V PC electrolytic 1MΩ. Digital multimeters generally have an input impedance much higher than 1MΩ and so they can be used to measure the sensor’s output voltage. However, the input impedance of an analog meter may not be high enough. The first step in identifying the leads is to set your DMM to DC volts (eg, 20V), then connect the negative lead of the DMM to chassis. That done, it’s a matter of starting the engine and probing the sensor’s leads with the DMM’s positive lead (a pin can be used to pierce the wire insulation but seal any holes with silicone afterwards to prevent corrosion). The sensor’s H+ lead will be at +12V, while its signal voltage lead will be at about 450mV. Once these two leads have been identified, switch off the engine and unplug the sensor. The H- terminal 1 22µF 16V PC electrolytic 4 10µF 16V PC electrolytic 4 220nF MKT polyester 4 100nF MKT polyester 1 10nF MKT polyester 1 3.3nF MKT polyester 1 1nF MKT polyester 1 22pF ceramic Trimpots 1 500Ω multi-turm trimpot (3296W type) (Code 501) (VR1) 3 5kΩ multi-turm trimpot (3296W type) (Code 502) (VR2-VR4) 2 1kΩ multi-turm trimpot (3296W type) (Code 102) (VR5) Resistors (0.25W, 1%) 4 560kΩ* 3 2.2kΩ 2 470kΩ 1 1kΩ 4 100kΩ 2 470Ω 1 82kΩ 3 150Ω 3 22kΩ 1 120Ω 1 20kΩ 1 62Ω 1 12kΩ 2 10Ω 2 10kΩ 1 0.1Ω 5W 2 4.7kΩ *(Two used for % oxygen in air readings) Sensor Parts 1 Bosch LSU4.2 broadband oxygen sensor Available from: TechEdge (http:// wbo2.com/lsu/sensors.htm part # [07200]) can now be identified – it’s the one that gives a resistance reading of typically 5Ω (and usually less than 10Ω) to the previously identified H+ terminal (warning: do not connect the meter probe to the previously identified signal terminal when making resistance measurements). The ground terminal is the one remaining. With Bosch sensors, two white leads are used for the heater, while a black lead is used for the signal and a grey lead is used for sensor ground. However, this does not apply in all cases. In some cars, the ECU will check that the sensor is connected and produce an error code if it detects that anything is amiss. In most cases, however, the S-curve signal from the Wideband Controller will be accepted siliconchip.com.au Bosch. Part # 0 258 007 200 Audi/VW Part # 021-906-262-B. 1 6-pin female connector for the sensor including 6 x 2.8mm female crimp spade terminals plus 6 end seals Available from: Techedge (http:// wbo2.com/cable/lsuconns.htm part # [CNK7200]) Or VW Part # 1J0-973-733 for the plastic shell only, type FEP FKG62,8/2FEP42122200. 1 8-pin circular multipole line socket Available from:TechEdge (http:// wbo2.com/cable/connkit.htm part # [P8PIN] Or www.farnell.com.au cat #8041563 1 6-way sheathed and shielded lead with 2x7.5A wires for heater. Available from: Techedge (http:// wbo2.com/cable/default.htm part # [DIY26CBL] for 2.6m long or part # [DIY40CBL] 4m long. Both parts include the 8-pin circular multi-pole line socket 1 8-pin circular multi-pole panel plug connector (microphone) Available from: Techedge (http:// wbo2.com/cable/connkit.htm part # [S8PIN] Or www.farnell.com.au cat #8041709 as valid but there are exceptions. First, the ECU may check the sensor’s impedance to determine if it is sufficiently heated (ie, when its impedance falls below a particular value). However, the impedance the ECU will measure at the Wideband Controller’s S-curve output will be 150Ω and this may be incorrect for some sensors. For the Bosch LSM11 narrowband sensor, the impedance is less than 250Ω when heated and so the 150Ω impedance for the S-curve output should be satisfactory. Other sensors may differ, however, and so the 150Ω output resistor may have to be changed to prevent an error code. No provision has been made to vary the S-curve output impedance to simulate the heating of the sensor siliconchip.com.au over time (ie, from a high value when cold to around 150Ω when hot). Usually, for a cold engine start, the ECU will wait until the engine is warm (as indicated by the temperature sensor in the cooling system) before readings from the oxygen sensor take place. By this time, the sensor will also be warm, with the S-curve output responding as it should to mixture variations and having a low impedance as expected by the ECU. Conversely, the sensor will already be hot for a warm engine start. If the ECU expects the S-curve output impedance to be high at engine start-up, then a timer such as the Flexitimer (SILICON CHIP, June 2008) can be used. This can be set to provide an open circuit connection between the S-curve output and the ECU for about 20 seconds after engine start, at which time the timer’s relay contacts close to make the connection. Alternative DIY Wideband Controller and Display Tech Edge designs wideband DIY (and pre-built) controllers. We have sold thousands worldwide since 2002. Our latest DIY design is the 2Y1. We also sell a 4 digit DIY display (the LD02) designed to team up with the 2Y1. We sell Bosch LSU (wideband) sensors suitable for the 2Y1 and other wideband units. Heater fault indications Some ECUs will indicate a fault if the heater leads to the oxygen sensor are disconnected. In this case, you will have to keep the original heater connection to the old oxygen sensor and mount it in a convenient place (eg, against the firewall). Just make sure that the heated sensor cannot be accidentally touched, as it can run very hot. Alternatively, you can make up a resistance box that has the same nominal resistance as the sensor’s heater element when hot. This should go in a diecast case and you would need to use resistors rated for the power. The power rating is calculated by assuming a 14.8V maximum supply and a 50% derating. For example, if the heater resistance is 12Ω, then 14.8V2 divided by 12Ω gives 18.25W. In practice, a 40W resistor would thus be required. A 12Ω 40W heater resistance could be simulated by connecting four 10W 47Ω resistors in parallel. Sensor response rate Another ECU check may involve the way the sensor responds to mixture changes in the exhaust gas. The ECU will expect the sensor output to be higher than 450mV for rich mixtures and less than 450mV for lean mixtures and the sensor’s response rate may be tested. For optimal set-up of the delay, the The 2Y1 has superior speed and accuracy compared to other DIY designs, and performance exceeds that of many commercial units costing up to several thousand dollars. The 2Y1 also has an inbuilt logger with 6 analog voltage inputs and an RPM and pulse input. An optional 1 Mbyte logger module is also available for storage when a laptop is inconvenient to use. The LD02 display is digitally connected (not via analog voltages!) for superior accuracy and can double as a monitor for analog voltages, collected from the 2Y1, or locally. LD02 can even be used with other wideband controllers that provide an analog voltage output. It can be used as a stand-alone display. 2Y1 DIY kit from LD02B DIY kit from Bosch LSU Sensor $99.00 + GST $49.00 + GST $97.00 + GST . . non-DIY units from $159.00 + GST . Both the 2Y1 and LD02 come as professional kits with double sided PCBs and some prebuilt and pretested SMD components. An online user forum as well as local telephone support is also available. Full construction details and further information from our website: http://wbo2.com/diy Tech Edge Pty. Ltd. (02) 6251 5519 October 2009  81 Using A Wideband Sensor In A Permanent Installation As a test, we substituted a wideband sensor for the narrowband sensor in a 2004 Holden Astra. The S-curve output from the Wideband Controller was then fed to the car’s ECU (in place of the output from the original sensor). This worked OK and no error codes were produced by the ECU. However, we did have to keep the heater circuit to the original narrowband sensor connected to achieve this result. In operation, the narrowband signal from the Wideband Controller cycles correctly above and below stoichiometric but it appears to be twice as slow in its response as the original narrowband sensor. A new narrowband sensor also had a slower response than the original sensor. The differences in the sensors are in the way the sensor is vented to the exhaust gas, the original narrowband sensor having side slits to allow fast gas entry. By contrast, the new narrowband sensor has its entry slits on the end while the wideband sensor uses small holes which are also at the end. As a result, the latter two sensors have a slower response because the gas is not replaced as quickly. So using a wideband sensor as a permanent installation may not be ideal in all cases but will be OK for testing mixtures. Whether or not it is completely successful as a permanent installation will depend on the sensor orientation to the exhaust gas flow. S-curve output from the Wideband Controller can be set to match the response of the original narrowband sensor. This adjustment is made using VR2 and can be as fast as the overall wideband response of <250ms when VR2 is adjusted for 0V on TP2. This can be increased up to an extra 1.2s when VR2 is set to that TP2 is at 5V, with shorter delays in between. For example, a setting of 2.5V will increase the overall wideband response delay by 600ms (ie, to 250 + 600 = 850ms). The correct setting for your vehicle can be easily determined if you have an oscilloscope. To do the test, make sure the original narrowband sensor is installed and connect the scope probe to the sensor’s output signal. Alternatively, an OBD (On-Board Diagnostics) scan tool that shows live or real-time parameter data can be used to monitor the sensor voltage if this feature is supported on your vehicle. When the engine is warm and idling, the sensor reading should oscillate above and below 450mV at a rate dependent on the sensor’s response rate and the ECU. By using the oscilloscope, the frequency of oscillation and the voltage can be directly measured. A typical narrowband sensor response is shown in Fig.19. Now replace the narrowband sensor with the wideband sensor and connect the S-curve output from the Wideband Controller to the sensor+ signal input of the ECU.That done, adjust VR2 so that the response appears to be similar to that from the narrowband sensor. Note that adjustments to VR2 can take up to 5s to have any effect, so take it slowly. If you don’t have an oscilloscope, monitor the narrowband sensor output using a DMM and then try to match the response when the Wideband Con- 0.55V TIME 0.45V 0.35V 1.25sec Fig.19: a typical narrowband sensor response with the engine warm and idling. The output oscillates above and below 450mV and can vary from just a few millivolts to about ±400mV (±100mV shown here). 82  Silicon Chip troller’s S-curve output is substituted. This method will not be very accurate, however. Alternatively, you may prefer not to bother trying to match the response time. In that case, set VR2 so that TP2 is at 1.25V. This will increase the normal Wideband Controller response by about 300ms (ie, to about 550ms), which should suit most vehicles. By the way, oxygen sensors do have a slower response as they age. This means that a faster response from the Wideband Controller can be used to simulate the narrowband sensor’s output when it was new. Finally, if the S-curve simulation proves unsuccessful, either because the engine runs poorly or the ECU logs a fault regardless of any attempts to match the response, then the narrowband sensor will have to be reinstalled. The Wideband Sensor will then have to be installed in a separate position. Other applications As indicated earlier in this article, the Wideband Controller can be set up to monitor the oxygen content in air. It can measure oxygen concentrations ranging from beyond the standard 20.9% in normal air right down to 0%. That makes it ideal for checking the oxygen content of the air in enclosed spaces such as fire bunkers and walkin cold storage containers, where the oxygen content can be depleted due to human respiration. Another application includes areas where oxygen is depleted due to combustion. This includes areas heated with gas, oil, coal or wood fires. Other instruments should also be used to ensure clean air, including those for monitoring carbon monoxide (CO) and flammable gases. In order to correctly read the oxygen content, the tip of the sensor must be exposed to the air under being monitored while the “lead end” of the sensor must be exposed to normal air. In other words, the sensor has to be able to use normal air as a reference. This means that the sensor must be mounted in the outer wall of the enclosed space, with its top section exposed to the outside air. The voltage output from the Wideband Controller is directly proportional to the oxygen content in percent. So a 2.09V reading represents an oxygen content of 20.9%, which is the oxygen SC content of normal outside air. siliconchip.com.au