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Russell Bull
08/13/05 22:44
Read: 721 times
Melbourne
Australia


 
#99363 - Engine analyser
Responding to: Farshid Jafari Harandi's previous message

for determining the RPM why do you think you need to sample a signal from the ignition coil primary? The signal from one spark plug is sufficient. For determining the spark advance, the spark triggers a timer, when the timer expires, it fires the flash light(normally at top dead centre). The value of this timer is the spark advance value. Measuring the timing for each spark plug seems of little value - most engine analysers allow you to view the signal from each spark plug as this is used to determine the combustion characteristics in each cylinder. The cylinder to cylinder timing is normally fixed mechanically or electrically.

I would suggest you get your hands on a commercial timing light to see how they do this. These can vary from the very cheap to very expensive - the circuitry tends to be similar. Most of the ones I've seen and used have a split ferrite core that clamps around the spark lead and a number of windings for the pickup coil - a simple transformer. For the flash, it is usually a 'ringing choke' style of converter charging a capacitor with about 200-300 VDC and a SCR dumping a small capacitor's chanrge into a trigger transformer for a xenon flash tube.

It is normally easier to measure the period between the sparks rather than the frequency. Derivatives with a PCA timer may help here although you have a capture on timer2. Also remember that the angle is a fraction of the period time value.

I wouldn't waste time using optocouplers - I rarely see use of these in automotive electronics. Best to be careful in pcb layout and protection circuitry. Since the electronics are normally powered from the vehicle electrics, optos add little value.




List of 45 messages in thread
TopicAuthorDate
Tachometer and engine timing tool      Farshid Jafari Harandi      08/13/05 22:06      
   Engine analyser      Russell Bull      08/13/05 22:44      
      RE : Engine analyser      Farshid Jafari Harandi      08/14/05 12:19      
         Engine analyser      Russell Bull      08/14/05 19:11      
            Xenon Flash Lights      Farshid Jafari Harandi      08/14/05 20:50      
               Xenon flash lights      Russell Bull      08/14/05 21:39      
                  Calculating RPM      Dan Adams      08/15/05 07:38      
                     RE: Calculating RPM      Farshid Jafari Harandi      08/15/05 14:10      
                  flash charge circuit      Farshid Jafari Harandi      08/15/05 14:16      
   Look at this then        Steve M. Taylor      08/14/05 07:15      
      I like it...      Farshid Jafari Harandi      08/14/05 12:20      
   Xenon      Neil Kurzman      08/14/05 16:51      
      Delay time < 10us      Farshid Jafari Harandi      08/14/05 20:31      
   Led Instead Xenon        Roberto Muņoz      08/17/05 08:02      
      Interesting idea, were I to make sutch a      Erik Malund      08/17/05 08:08      
         White is better for finding the TDC mark      Farshid Jafari Harandi      08/17/05 14:13      
            If white light is required and what I ha      Erik Malund      08/18/05 06:08      
               Good link      Farshid Jafari Harandi      08/18/05 14:07      
      Nice !!      Farshid Jafari Harandi      08/17/05 14:08      
         I do not work with white LEDs but with r      Erik Malund      08/17/05 14:30      
            White LED      David Smith      08/18/05 07:01      
               got curious and googled      Erik Malund      08/18/05 07:12      
               got curious and googled      Erik Malund      08/18/05 07:13      
               Hmm      Steve M. Taylor      08/18/05 07:35      
                  Sure it's not, but      Farshid Jafari Harandi      08/18/05 14:07      
                     New prototype circuit      Farshid Jafari Harandi      08/19/05 01:07      
                        I would recommend a constant current cir      Erik Malund      08/19/05 06:05      
                           Current regualtor      Farshid Jafari Harandi      08/19/05 10:02      
                              C2 may blow your LED, what is it there f      Erik Malund      08/19/05 11:19      
                              Led ON time      Russell Bull      08/19/05 22:51      
                                 6000 RPM      Farshid Jafari Harandi      08/20/05 12:42      
                                    6000RPM      Stuart Hall      08/21/05 01:06      
                                       Can't comment on that now      Farshid Jafari Harandi      08/21/05 14:30      
                  saw an article and while this probably      Erik Malund      08/18/05 14:12      
                     Thanks      Steve M. Taylor      08/18/05 14:33      
                        timing light      Russell Bull      08/18/05 23:09      
                           unanswered questions      Farshid Jafari Harandi      08/19/05 01:06      
                  White LED v Xenon tube      David Smith      08/19/05 01:19      
                     'difficult' to drive      Farshid Jafari Harandi      08/19/05 04:25      
                        Big LEDs      Steve M. Taylor      08/19/05 04:57      
                           So Thats it !      Farshid Jafari Harandi      08/19/05 09:59      
                              Who has said ir has to be just one, can      Erik Malund      08/19/05 11:21      
                                 C is for stability ?      Farshid Jafari Harandi      08/20/05 12:32      
                     I have no idea, but I have seen I do not      Erik Malund      08/19/05 06:13      
                        White LED 'drivers'      David Smith      08/20/05 14:31      

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