circuit harness wiring

Thursday, December 26, 2013

Simple Micro volt probe Circuit Diagram

The current tracer helps locate a defective IC that is loading down the power supply. The tracer amplifies the small voltage drop caused by current flow along a fraction of an inch of PC wiring and drives an ordinary microammeter. Needle-point test probes are used to contatt the edge of a PC trace and to follow the current to determine which branch the current takes.

One-half of a dual 741 op amp forms a dc amplifier with ac feedback to prevent oscillations and hum-pickup problems.It drives a 50-to-100 Âµ meter. The other op amp provides a center tap for the 9 V battery supply and zero adjustment with R4. Two diodes protect the meter. Resistor Rl eliminates the necessity for shorting the probes when the meter is zeroed. The value of 1 ohm is large when compared with the resistance of the meter leads plus the bridged portion of PC wiring.

Micro-volt probe Circuit Diagram

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Saturday, October 5, 2013

Logic Probe With Sound Circuit

This logic probe can be selected to operate on TTL or CMOS logic levels, depending on switch S1. A string of resistors associated with switch S1 sets the threshold levels for a window comparator comprising IC1a and IC1b. Depending on whether the level applied to the probe is high or low, the window comparator turns on LED1 (high) or LED2 (low). The 1.2M and 680k resistors set the probe signal to a midrange value when the probe is open-circuit, thereby preventing either LED from being lit.

Circuit diagram:

Logic Probe With Sound Circuit digram

If a pulse signal is present, the output of IC1a will toggle the clock input of flipflop IC2a. This drives LED3 which either lights for each pulse or continuously, depending on the setting of switch S2. Finally, the outputs of IC1a & IC1b are connected by diodes D5 & D6 to the base of transistor Q1 which is connected to the Reset input of flipflop IC2b. This has a piezo sounder (not buzzer) connected between its Q and Q-bar outputs so that it produces a sound which echoes the input pulse signal.

Author: Tom Hughes Copyright: Silicon Chip Electronics

Wednesday, April 10, 2013

Lambda Probe Readout For Carburettor Tuning

A lambda probe (or oxygen sensor) can be found on the exhaust system of most cars running on unleaded fuel. Having reached its normal operating temperature (of about 600 degrees Celsius!) the lambda probe supplies an output voltage proportional to the amount of residual oxygen measured in the exhaust gas.

This information is indicative of, among others, the air/fuel ratio supplied by the carburetor(s) and hence the combustion efficiency. In modern car (and motorcycle) engines, this information is used to (electronically) adjust engine parameters like ignition timing and fuel injection. The indicator described here is intended for permanent installation on a motorcycle of which the air/fuel ratio needed to be watched, with the obvious aim engine power tuning after ﬁtting a different set of carburetors. Apart from this obvious technical use the unit’s bright LEDs will no doubt attract the attention of curious motorcyclists.

Lambda Probe Readout For Carburettor Tuning

At the local junkyard a single-wire lambda probe may be salvaged from a wrecked car. Once a suitable nut has been found, the probe can screwed into the exhaust pipe of the motorcycle, at about 30 cm from the cylinders. Since we’re talking of welding and drilling in an expensive (chrome-plated) exhaust pipe, you may ﬁnd that actually ﬁtting the probe is best left to specialists! The starting point for the design of a suitable electronic indicator is that in the noble art of carburetor tuning an air/fuel ratio of 14.7 to 1 is generally considered ‘perfect’, the range covering 16.2 to 1 (‘lean’) to 11.7 to 1 (‘rich’). The perfect ratio typically corresponds to a probe output voltage of 0.45 V.

Referring to the circuit diagram, that is the input level at which 5 of the 10 LEDs will light, including the green one, D5. If one of the red LEDs lights, the mixture is definitely too rich. Note that in general it is better to have a mixture that is a little to rich than one that’s on the lean side, hence a yellow LED lights between the green LED and the ﬁrst red one. Also note that the engine needs to be at its normal operating temperature before a meaningful indication is obtained.

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