I am working on a project design for a speedometer converter. I would like for it to be a universally adjustable converter, but my initial design is very job specific.
in this particular case, my design must adapt the mechanical speedometer drive from an old VW bus to work with an instrument cluster from a newer model VW passat. to do this, I am taking a frequency signal from an electronic speed sender driven from the cable, which pulses 4 times per wheel rotation, and I need to multiply this signal a precice amount of times to match the signal required by the cluster.
My plan is to use two NJM4151 VFC/FVC IC's. where I will first convert the frequency to voltage with one, then convert the voltage back to a different frequency ratio with the second. Inevitably, I should be able to adjust this ratio by the turn of a single potentiometer.
the datasheet for the NJM4151 can be found here:
http://semicon.njr.co.jp/njr/hp/fileDownloadMedia.do?_mediaId=419
Following the datasheets Figure 5 schematic for single supply FVC, I have the first part of my schematic on my test board right now. it is functional, but I am having a little trouble with the math.
Some Information about the circuit in question:
---the circuit needs to operate from 0hz, (zero miles per hour) to at least 140hz, (@100 miles per hour, with 4 pulses per wheel rotation and ~800 wheel rotations per mile) for the sake of universal applications, a wider range may be needed, but unlikely to exceed the 1khz range ever.
----the voltage of the source is 12v, (automotive application) but it will be irregular, so I will probably use a regulator to bring it down to 10v stable.
the datasheet says this IC can "operate with a full scale frequency anywhere from 1.0hz to 100khz" So I dont think I will have any trouble with low speeds and this IC.
So my question is,
what values do I need to employ for components Rs, Rb, Ro, Co, for a circuit that will operate with a full scale frequency input of 0-1khz and an output of 0v to something less than 10v (since my supply will probably be a regulated 10v), with the ability to tune the frequency scale up or down with the turn of a single pot?
I have done a bit of trial and error, and tried to work out the formula in reverse to find my values for these components, but I seem to be missing some critical step. my figures just dont come out right on the proto board.
Note: I have read through this thread http://forum.allaboutcircuits.com/showthread.php?p=7150 where hgmjr wrote a nice explanation of the theory of this circuit and his included examples. it was very informative, and given time I think I might be able to answer my own questions, but I am hopeing someone can help me find the missing piece of the problem.
So if anyone has any input on this, I would greatly appreciate it. I know a lot of VW owners who are looking to install a modern VR6 engine into their busses will also be very greatful.
in this particular case, my design must adapt the mechanical speedometer drive from an old VW bus to work with an instrument cluster from a newer model VW passat. to do this, I am taking a frequency signal from an electronic speed sender driven from the cable, which pulses 4 times per wheel rotation, and I need to multiply this signal a precice amount of times to match the signal required by the cluster.
My plan is to use two NJM4151 VFC/FVC IC's. where I will first convert the frequency to voltage with one, then convert the voltage back to a different frequency ratio with the second. Inevitably, I should be able to adjust this ratio by the turn of a single potentiometer.
the datasheet for the NJM4151 can be found here:
http://semicon.njr.co.jp/njr/hp/fileDownloadMedia.do?_mediaId=419
Following the datasheets Figure 5 schematic for single supply FVC, I have the first part of my schematic on my test board right now. it is functional, but I am having a little trouble with the math.
Some Information about the circuit in question:
---the circuit needs to operate from 0hz, (zero miles per hour) to at least 140hz, (@100 miles per hour, with 4 pulses per wheel rotation and ~800 wheel rotations per mile) for the sake of universal applications, a wider range may be needed, but unlikely to exceed the 1khz range ever.
----the voltage of the source is 12v, (automotive application) but it will be irregular, so I will probably use a regulator to bring it down to 10v stable.
the datasheet says this IC can "operate with a full scale frequency anywhere from 1.0hz to 100khz" So I dont think I will have any trouble with low speeds and this IC.
So my question is,
what values do I need to employ for components Rs, Rb, Ro, Co, for a circuit that will operate with a full scale frequency input of 0-1khz and an output of 0v to something less than 10v (since my supply will probably be a regulated 10v), with the ability to tune the frequency scale up or down with the turn of a single pot?
I have done a bit of trial and error, and tried to work out the formula in reverse to find my values for these components, but I seem to be missing some critical step. my figures just dont come out right on the proto board.
Note: I have read through this thread http://forum.allaboutcircuits.com/showthread.php?p=7150 where hgmjr wrote a nice explanation of the theory of this circuit and his included examples. it was very informative, and given time I think I might be able to answer my own questions, but I am hopeing someone can help me find the missing piece of the problem.
So if anyone has any input on this, I would greatly appreciate it. I know a lot of VW owners who are looking to install a modern VR6 engine into their busses will also be very greatful.