A Change of Plan: -

Date	Discussion
March 2023	This page was intended to be all about setting up the Speeduino. However, there has been a problem that has caused a fairly major change of plan. The main timing signal used to synchronise the engine mechanics with the Speeduino electronics was to be taken from the mechanical points in the distributor. It is a simple and very cost effective solution. However, it is traditionally a very noisy signal, electronically, that has to be very carefully filtered and also reduced in amplitude, from 12volts to 5volts. I have built a number of successively more complex noise filter circuits and the most recent is described, in some detail, in a preceding chapter. I also built a tester for the points signal, consisting of an old distributor, with its original mechanical points, coil and spark plug. The distributor shaft was driven by an electric motor whose speed could be varied to simulate different engine revs. The results have been disappointing. Not only is it difficult to effectively filter all the noise that occurs across the full operating rev. range, but the timing of the signal, in relation to the mechanics, I now realise, is somewhat variable as well. Also, minor adjustments to the points, or even just cleaning them, can cause significant timing changes, which makes life very difficult for the ECU. One solution would be to use a more modern distributor that doesn't use mechanical points at all but uses a solid state sensor instead. This approach would certainly improve matters. However, "points", of any kind, are deliberately designed to alter their timing relationship with the engine, in order to adjust the ignition timing for special situations, such as sustained high speed or hard acceleration. All of which means that the ECU can receive a very confusing set of signals, making its job harder than it might otherwise be. Not only "harder", but therefore, unreliable as well. Hardly a desirable situation. As a result of these issues, the difficult decision was made to abandon the idea of using the distributor points signal to drive the ECU and look for something else. Most modern cars use one, or more, separate sensors to drive their ECUs. These may be in the distributor, if they even have one, or they may be on the crankshaft or camshaft, or both. They usually consist of a rotating disk, with "teeth" or slots, that can be detected as they move past a sensor. There are three main types, optical, magnetic and proximity. Optical sensors have an infrared light source positioned behind a perforated disk, so that holes in the disk can be detected as they pass. Optical sensors are subject to dirt and the light source has a specific life. Magnetic sensors use a disk, with tiny, embedded magnets, making it expensive to produce. The magnets can be detected as they pass a Hall Effect type semiconductor, which is not only very reliable, but produces a very convenient output waveform. However, it can also be subject to stray magnetic interference from alternators and the like. Proximity sensors, more properly called Variable Reluctance ("VR") sensors, react to the presence or absence of ferrous metal. They contain their own magnet and a coil, so that the disk attached to the machinery can be a plain iron disk with "teeth". They have no moving parts, nothing to wear out, relatively simple to make and are much less subject to noise or interference. The Speeduino has provision for utilising a VR signal, from a crank trigger disk, with the addition of a small, and readily available, extra processing module. It simply plugs into a socket already provided on the circuit board for the purpose. Since Rhapsody's engine was built in 1965, long before VR sensors were invented, it needs to be modified to be able to produce a suitable signal for the ECU. A common approach is to attach a toothed wheel to the front of the crank shaft, usually directly onto the harmonic balancer, behind the fan pulley, and mount the sensor somewhere conveniently nearby. Like all things, it's so much easier if someone has done it before. One of the advantages of using a very common engine is that not only have other people already addressed the issue, they actually provide a kit of ready made parts so that you don't have to "reinvent the wheel"! Just bring money! So back to the trusty Internet to find a Crank Trigger Kit suitable for Rhapsody's Holden 149 engine. Very soon, I found Luke Hoffman from Sonic Injection. Not only does he offer exactly the right kit of parts, but he's also located just a few kilometres away, which is very convenient.

Date

Discussion

March 2023

This page was intended to be all about setting up the Speeduino. However, there has been a problem that has caused a fairly major change of plan.

The main timing signal used to synchronise the engine mechanics with the Speeduino electronics was to be taken from the mechanical points in the distributor. It is a simple and very cost effective solution. However, it is traditionally a very noisy signal, electronically, that has to be very carefully filtered and also reduced in amplitude, from 12volts to 5volts. I have built a number of successively more complex noise filter circuits and the most recent is described, in some detail, in a preceding chapter.

I also built a tester for the points signal, consisting of an old distributor, with its original mechanical points, coil and spark plug. The distributor shaft was driven by an electric motor whose speed could be varied to simulate different engine revs. The results have been disappointing. Not only is it difficult to effectively filter all the noise that occurs across the full operating rev. range, but the timing of the signal, in relation to the mechanics, I now realise, is somewhat variable as well. Also, minor adjustments to the points, or even just cleaning them, can cause significant timing changes, which makes life very difficult for the ECU.

One solution would be to use a more modern distributor that doesn't use mechanical points at all but uses a solid state sensor instead. This approach would certainly improve matters. However, "points", of any kind, are deliberately designed to alter their timing relationship with the engine, in order to adjust the ignition timing for special situations, such as sustained high speed or hard acceleration. All of which means that the ECU can receive a very confusing set of signals, making its job harder than it might otherwise be. Not only "harder", but therefore, unreliable as well. Hardly a desirable situation.

As a result of these issues, the difficult decision was made to abandon the idea of using the distributor points signal to drive the ECU and look for something else.

Most modern cars use one, or more, separate sensors to drive their ECUs. These may be in the distributor, if they even have one, or they may be on the crankshaft or camshaft, or both. They usually consist of a rotating disk, with "teeth" or slots, that can be detected as they move past a sensor. There are three main types, optical, magnetic and proximity. Optical sensors have an infrared light source positioned behind a perforated disk, so that holes in the disk can be detected as they pass. Optical sensors are subject to dirt and the light source has a specific life. Magnetic sensors use a disk, with tiny, embedded magnets, making it expensive to produce. The magnets can be detected as they pass a Hall Effect type semiconductor, which is not only very reliable, but produces a very convenient output waveform. However, it can also be subject to stray magnetic interference from alternators and the like. Proximity sensors, more properly called Variable Reluctance ("VR") sensors, react to the presence or absence of ferrous metal. They contain their own magnet and a coil, so that the disk attached to the machinery can be a plain iron disk with "teeth". They have no moving parts, nothing to wear out, relatively simple to make and are much less subject to noise or interference.

The Speeduino has provision for utilising a VR signal, from a crank trigger disk, with the addition of a small, and readily available, extra processing module. It simply plugs into a socket already provided on the circuit board for the purpose.

Since Rhapsody's engine was built in 1965, long before VR sensors were invented, it needs to be modified to be able to produce a suitable signal for the ECU. A common approach is to attach a toothed wheel to the front of the crank shaft, usually directly onto the harmonic balancer, behind the fan pulley, and mount the sensor somewhere conveniently nearby. Like all things, it's so much easier if someone has done it before. One of the advantages of using a very common engine is that not only have other people already addressed the issue, they actually provide a kit of ready made parts so that you don't have to "reinvent the wheel"! Just bring money!

So back to the trusty Internet to find a Crank Trigger Kit suitable for Rhapsody's Holden 149 engine. Very soon, I found Luke Hoffman from Sonic Injection. Not only does he offer exactly the right kit of parts, but he's also located just a few kilometres away, which is very convenient.