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Using A Wideband O2 Sensor In Your Car, Pt.2

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.

By John Clarke

Building 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.

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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.

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 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, taking 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.

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The completed PC board is mounted inside a diecast metal case on plastic stand-offs.

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 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.

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 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).

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