Showing posts with label Tuning. Show all posts
Showing posts with label Tuning. Show all posts
Saturday, October 18, 2014
Lambda Probe Readout For Carburettor Tuning circuit and explanation
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. 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.
Apart from this obvious technical use the unit’s bright LEDs will no doubt attract the attention of curious motorcyclists. 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.
Thursday, October 2, 2014
Tuning Fork Simulator Circuit Diagram
- This signal is then buffered by gates N3 . . . N6 and the balanced output A stage gives a level sufficient to drive a small loudspeaker. ln spite of the current consumption of 65 mA, a standard 9 V battery (preferably alkaline-manganese) will suffice, because tuning forks are by their nature used for short periods only. lf the fork is used for longer periods, it might be advisable to consider a rechargeable battery.
- An oscillator, a divider, a loudspeaker and a battery are all that is required. T0 be useful, an electronic tuning fork must, of course, be a compact unit.
- As the use of special, and therefore oostly, crystals was precluded, a little research showed that it would be possible to use relatively simple and standard components.
- The oscillator is constructed a- round gates N1, N2 and tuned to 1,000,120 Hz (with a frequency counter if possible), by means of trimmer C2.
- A standard tuning fork produces a tone of 440 Hz, that is, the inter- national A (orchestral pitch). lt is not very difficult to make an elec- tronic alternative.
- It appeared that the required frequency can be derived from a readily available 1 MHz crystal which, by means of a trimmer, can be pulled to 1,000,120 Hz which is the nearest frequency containing a whole num- ber times 440 Hz.
- The oscillator output is fed to lC2 which divides; bv 227;; l2° + 25 + 26 + 27 +;,*1). practically symmetrical signal of 440 Hz is then available at output 011 of lC2.
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