where is speed sensor?
Discussion
just finished fitting my defi display which has an input to display vehicle speed. just need to splice into speed sensor output.
i found the speed sensor signal wire at the back of the speedo which comes from my speed sensor fitted to the front right hub.
problem is when i connect the defi to this signal, the speedo stops working and the defi doesnt register an input either. i think the defi is sinking the signal leaving both units without an input.
i know obes fitted the same display to his noble and hooked up behind the speedo and his worked, i have had a mail from him to confirm this. the big difference is that his had the speed sensor fitted to the gearbox.
i have had a look around the box and found a cut wire tapped up with the correct colour wires that would have connected to a gearbox sensor but cant see where the sensor would fit.
my idea was to fit a second sensor to the gearbox, let the speedo get a signal from the hub as it does now and feed the defi from the gearbox sensor.
anybody tell me, a pic would be even better, where i would expect to see the sensor fitted
cheers
sean
i found the speed sensor signal wire at the back of the speedo which comes from my speed sensor fitted to the front right hub.
problem is when i connect the defi to this signal, the speedo stops working and the defi doesnt register an input either. i think the defi is sinking the signal leaving both units without an input.
i know obes fitted the same display to his noble and hooked up behind the speedo and his worked, i have had a mail from him to confirm this. the big difference is that his had the speed sensor fitted to the gearbox.
i have had a look around the box and found a cut wire tapped up with the correct colour wires that would have connected to a gearbox sensor but cant see where the sensor would fit.
my idea was to fit a second sensor to the gearbox, let the speedo get a signal from the hub as it does now and feed the defi from the gearbox sensor.
anybody tell me, a pic would be even better, where i would expect to see the sensor fitted
cheers
sean
alex s said:
IIRC it is only the 5 speeds that have the sender on the gearbox.
When swapping to a six speed box, one of the things you have to do is fit a sensor for the speedo feed by the wheel, so I am guessing that the six speed does not have a sensor ( or the ability) on the gearbox.
HTH
Alex
that would make perfect sence to what i have seen/found on mine. have contacted defi regarding the problem so hopefully they will offer some adviceWhen swapping to a six speed box, one of the things you have to do is fit a sensor for the speedo feed by the wheel, so I am guessing that the six speed does not have a sensor ( or the ability) on the gearbox.
HTH
Alex
Wasn't me, but I did work out for whoever it was that asked it that you would need an "open collector" input on the secondary device if you want to use the speedo sensor that feeds the speedo.
Alternativly get a simple op-amp circuit made up to buffer the signal before feeding each device.
J
Alternativly get a simple op-amp circuit made up to buffer the signal before feeding each device.
J
joust said:
Wasn't me, but I did work out for whoever it was that asked it that you would need an "open collector" input on the secondary device if you want to use the speedo sensor that feeds the speedo.
Alternativly get a simple op-amp circuit made up to buffer the signal before feeding each device.
J
anyway we can have a chat mate?Alternativly get a simple op-amp circuit made up to buffer the signal before feeding each device.
J
right have fixed this problem and thought i would post some feedback in case somebody else has the same issue whe fitting a device which requires an input from the speed sensor.
basicaly the noble proximity sensor at the front wheel produces a 12v pulse at a rate of 85 pulses per second at 40 mph. when viewed on a scope this is a perfect square wave. however then the signal is in its off state there is not connection to ground. ie it is just a 12v pulse.
the defi display has a pull up resister on its input line which pulls the input up to 5v. the defi then looks for a pulse on its input which grounds or pulls this 5v down to ground.
so when connected up this means the noble speedo allways has at least 5v on its input (from the defi) so doesnt see the signal which now pulses from 5v to 12v in a square wave as being a full pulse therefore doesnt react.
the defi doesnt gets its input grounded so also doesnt react.
solution.
i used a common npn transister (2n222) and two resisters (110k and 22k) to decouple the two signals and create a ground pulse for the defi.
basically feed the noble speed signal through the 100k resister onto the base of the transister, then take the base of the transister to ground through a 22k resister.
this makes the transister switch on and off at the same frequenzy as the speed signal.
connect the emiter of the transister to ground and the collector to the defi input.
as the transister switches on and off the defi gets its input grounded throught the transister
simple really, a bit of time sat with a note pad, oscilliscope and trying to remember what i learnt at college 20 years ago was all that was needed.
usefull if you have a sat nav that dont respond to speed pulse or other simular device
basicaly the noble proximity sensor at the front wheel produces a 12v pulse at a rate of 85 pulses per second at 40 mph. when viewed on a scope this is a perfect square wave. however then the signal is in its off state there is not connection to ground. ie it is just a 12v pulse.
the defi display has a pull up resister on its input line which pulls the input up to 5v. the defi then looks for a pulse on its input which grounds or pulls this 5v down to ground.
so when connected up this means the noble speedo allways has at least 5v on its input (from the defi) so doesnt see the signal which now pulses from 5v to 12v in a square wave as being a full pulse therefore doesnt react.
the defi doesnt gets its input grounded so also doesnt react.
solution.
i used a common npn transister (2n222) and two resisters (110k and 22k) to decouple the two signals and create a ground pulse for the defi.
basically feed the noble speed signal through the 100k resister onto the base of the transister, then take the base of the transister to ground through a 22k resister.
this makes the transister switch on and off at the same frequenzy as the speed signal.
connect the emiter of the transister to ground and the collector to the defi input.
as the transister switches on and off the defi gets its input grounded throught the transister
simple really, a bit of time sat with a note pad, oscilliscope and trying to remember what i learnt at college 20 years ago was all that was needed.
usefull if you have a sat nav that dont respond to speed pulse or other simular device
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