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Feb 19, 2021 14:35:23 GMT
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I looking to re-purpose an old rev counter (possibly from an XJ6 as they’re cheap) and looking for a way of triggering it.
Traditionally it gets a feed from the points; two pulses every rotation for a four cylinder, three pulses per rotation for a six cylinder (XJ6) etc.
Now I figure I could easily generate the desired number of pulses per rotation from a disc with alternating black & white segments and an IR LED & photo-transistor combo.
However I would need a small amplifier to boost the signal accordingly, 20 years ago I could have designed such a circuit in my sleep but it’s been too long since I did any circuit design.
Does anyone know of a simple circuit for triggering a rev-counter in this manner? I’ve tried Google searching but I keep getting circuits for making a digital rev counter which isn’t what I want at all. So I figured I’d ask here.
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Feb 19, 2021 15:03:46 GMT
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That shouldn't be too hard, but optical sensors aren't used much on cars due to propensity for build up of filth on the sensor affecting reliability. Have you considered sticking magnets on a disc and a hall effect switch? In theory that should be able to connect directly to the points input on the tacho.
Salvaging a motor from an electric adjust seat with a memory function should yield a suitable magnetic disc and pick up plus some suitable mounting hardware.
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Feb 19, 2021 15:04:37 GMT
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Feb 19, 2021 21:14:34 GMT
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Thanks for the link, that should do exactly what I want.
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squonk
Part of things
Posts: 855
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Feb 20, 2021 17:35:37 GMT
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2004 Chevrolet Avalanche Z71
2005 Mercedes CLK320 Cabriolet
1996 Mercedes C180 Elegance Auto Saloon
1996 Rover 620Ti (Dead fuel pump)
1992 Toyota HiLux Surf
1987 Range Rover Vogue (Rusty)
1992 Range Rover Vogue SE (More Rusty)
2006 Chrysler Grand Voyager
2008 Corsa 1.4 Design
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Feb 20, 2021 18:11:45 GMT
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is there any reason why you cant just wire it your coil or w terminal on alternator if its a diesel
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Feb 20, 2021 21:06:08 GMT
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This is what I used to drive injectors from a lower voltage and tiny current signal generator. You wouldn't need the diode accross the injector, it's there to prevent a spike from the injector coil. I used a FQP30N06L mosfet Works a treat.  |
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Last Edit: Feb 20, 2021 21:11:47 GMT by kevins
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squonk
Part of things
Posts: 855
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is there any reason why you cant just wire it your coil or w terminal on alternator if its a diesel Diesel tachos are different to petrol ones. The petrol one is expecting to see a 0 - 12v (nominal) square wave pulse whereas a diesel one will use a +/- 18v (unrectified so above 12v) sine wave. The frequency of pulse will be out as well. |
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2004 Chevrolet Avalanche Z71
2005 Mercedes CLK320 Cabriolet
1996 Mercedes C180 Elegance Auto Saloon
1996 Rover 620Ti (Dead fuel pump)
1992 Toyota HiLux Surf
1987 Range Rover Vogue (Rusty)
1992 Range Rover Vogue SE (More Rusty)
2006 Chrysler Grand Voyager
2008 Corsa 1.4 Design
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Feb 21, 2021 13:45:00 GMT
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is there any reason why you cant just wire it your coil or w terminal on alternator if its a diesel Diesel tachos are different to petrol ones. The petrol one is expecting to see a 0 - 12v (nominal) square wave pulse whereas a diesel one will use a +/- 18v (unrectified so above 12v) sine wave. The frequency of pulse will be out as well. yes i understand that just wondered what he was fitting it to, to see if there was a easier way to do it that a trigger wheel. like fitting a diesel rev counter into a classic clock if its diesel. or the small circuit to connect wasted spark coils up if that whats being used |
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