My understanding of electronics and circuits is limited... but I am pretty good at figuring things out with a hint or two.

I have a motorcycle and I am looking to simplify the gauge cluster. Basically eliminate the existing tachometer and fuel gauge with just warning lights. So, I would like a LED to illuminate when fuel is low, and RPM's hit the redline. Since I already have the gauges, I know the cluster is receiving a signal of varying "strength" (term?) from the igniter and the fuel tank. What I want to do is monitor these signals and when the gauge reads almost empty and the RPM's read 11,000 a light comes on.... one for each obviously.

Is their some sort of switch that I can connect that turns on when these conditions are met? I have read something about a "Schmitt Trigger" that seems like it might work? I understand that I would have to calculate or get the specifications of both the tach and fuel sender signals. But can I buy a switch that is preset to turn on and off based on a range? If not... what might I be looking for?

I am trying to keep this very simply and minimize the electronic components involved. I have attached pics of the wiring diagrams for both if that helps.



Thanks in advance for any tips or input you might provide.

 

The tachometer is probably not receiving a level that represents the RPM, but a series of pulses, one pulse for revolution ot one pulse for each spark. So the frequency of the pulses changes engine speed.

 

The tachometer is probably not receiving a level that represents the RPM, but a series of pulses, one pulse for revolution ot one pulse for each spark. So the frequency of the pulses changes engine speed.

I agree.... so is their a switch that would trip when a certain numbers of pulses were received?

 

I am scratching my head as to why anyone would want to do this. Especially a warning light for fuel. By the time the light comes on (assuming it does come on and does not stay off do to a fualt of your design and/or build), it might already be too late.

Not to mention, it is going to be very difficult to manufacture something as aesthetically pleasing as what the manufacturer provided.

I think this is yet another case of a solution looking for a problem.

 

A gauge has the advantage that you can see a trend. A simple on/off LED would give you no warning of an impending fuel/engine problem. Like Spinnaker, I can't see why you would want to 'simplify the gauge cluster'. This seems to be a case of 'improving it worse'. That said, once you can provide sufficient information about the gauge input signals (pulse frequency range and voltage range) it should be possible to design a circuit to do what you want.

 

I am scratching my head as to why anyone would want to do this. Especially a warning light for fuel. By the time the light comes on (assuming it does come on and does not stay off do to a fualt of your design and/or build), it might already be too late.

Not to mention, it is going to be very difficult to manufacture something as aesthetically pleasing as what the manufacturer provided.

I think this is yet another case of a solution looking for a problem.

I have had this bike for many years. I already know the revs and the powerband, I just need a reminder when I go to the redline.

I regards to gas level my thought was I could set the light to go on when I have a gallon left, or whatever level I chose based on the voltage from the gauge. Just like in most modern cars... an extra reminder you are getting low.

I wasn't really trying to explain the why as I felt it would detract from the questions I had, but basically I just want the speedo which to me will be much cleaner than the current configuration.

 

A gauge has the advantage that you can see a trend. A simple on/off LED would give you no warning of an impending fuel/engine problem. Like Spinnaker, I can't see why you would want to 'simplify the gauge cluster'. This seems to be a case of 'improving it worse'. That said, once you can provide sufficient information about the gauge input signals (pulse frequency range and voltage range) it should be possible to design a circuit to do what you want.

The fuel light is just like in a car, a secondary reminder fuel is low. Thank you for the feedback on the type of circuit I would need.

 

Hi

Might be able to use LM29x7 FVC in a speed switch configuration. When the frequency of the impulses reach 11,000 RPM
the LED would light up. But you would need to figure out the tacho signal output pulse range vs rpm. You might be able to get this info from the tacho specs.

eT