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Need a Tachometer — Parallax Forums

Need a Tachometer

ii_awesumii_awesum Posts: 2
edited 2005-04-09 19:01 in BASIC Stamp
Hi all, just registered on this site.

I'm looking for design ideas to make a reasonably·accurate automotive tachometer for a point based V8.· and reading into a legacy BS2-IC.· If it's (likely) already been done, would anyone share their efforts?· I am hoping to build an engine monitoring interface and data logging into a Pocket PC.· I prefer not to use hall effect but rather use the existing pulse based signal going to the analogue tach.

Many thanks in advance.
Mike

Comments

  • GDGD Posts: 1
    edited 2004-09-14 16:31
    Are you going to try and transmit the data wirelessly? I was thinking that it would be great to be able to see what was going on in the car as I watched it on the track. I would like to hear if anyone has done this or has some ideas.
    Thanks
    Gary
  • ii_awesumii_awesum Posts: 2
    edited 2004-09-14 18:45
    For now I intend to connect the PDA via serial cable.· The PDA is also my GPS on another port.· ·My biggest concern is consuming too many cycles on the BS2 as I need it to monitor other environmentals and just dump flat strings of data for GUI display/logging on the PDA (or laptop if I go that route).·

    Perhaps there is already a cost effective prefab tach chip/module that outputs serial RPM data without too much supporting components?
  • BriefmarkBriefmark Posts: 10
    edited 2004-09-14 19:37
    To give you an idea of what is commerically available, MaxQData makes a Pocket PC based box which does what you want to do.· See http://www.maxqdata.com/· for more info.· I don't think it uses a Stamp however.· My son has one of the units, and it works quite well.

    Fred

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  • Gerry ShandGerry Shand Posts: 45
    edited 2004-09-22 22:21
    The way I would do this is as follows:

    a. set up a magnet or similar pick up circuit on the ditributor's rotor.

    b. run into a pulse conditioning circuit.

    c. run the output of the pulse conditioning circuit into the stamp through one input using the COUNT command. You would have to do some experimenting for the sample time but it would probably be between 100 ms and 1 s.

    d. at this point you can have the stamp re-transmit the tachometer data digitally by a serial link to a wireless transmitter, an LCD display designed to handle serial data from the stamp, or any other device with a serial input (may need a conversion chip to shift the voltage levels).

    The advantage to doing it this way is you have the data coming in digitally that is then processed by the stamp and then retransmitted to wherever using digital techniques. This means only one conversion is done and you do not have to worry about instrument drifting and any necessary re-calibration required.

    HTH.

    Gerry Shand
  • Eric REric R Posts: 225
    edited 2004-09-25 03:12
    Check out the datasheet for the LM2907
    I think you will find it to be what you are looking for.
  • hisidehiside Posts: 1
    edited 2005-04-09 19:01
    I am trying to do a similar concept of a tachometer funtion from an engine ignition signal with RPM limits to perform functions.· Has anybody done a tachometer circuit using a BS2?

    Thanks for the help.
  • truetechtruetech Posts: 6
    A fully digital car tachometer IS possible with a Basic Stamp 2sx chip. I built one that is not only fast, but it also runs the speedometer. These two instruments in any car need to be extremely responsive. That is why you need to dedicate one chip to display just the functions that require a high response time (this excludes things like oil pressure, fuel level, voltage and temperature which are a piece of cake with the RCTIME function). To effectively make this happen, you need to use the PULSIN function (not COUNT). Trust me, I really tried to make it work with COUNT, but the response just was not fast enough. The one I built is tied into an LS1 engine in a Camaro that I race and it's dead accurate. A couple things required to make this work is a good understanding of the integer math that limits Basic Stamps (but also makes them fast). Calculating the frequency requires an equation that generates the Period based on inputs from the PULSIN function. Then some interesting synthetic division (to get the accuracy required) in order to calculate the frequency and finally the RPM or Speed (all these calculations may sound like a lot, but the SX chews them up pretty fast). I also added a rate change filter algorithm to limit spikes. The calculated values get fired out in serial form to a MAX7219 chip for a combination 4 digit seven segment LED display and 32 individual LED's to form a bar graph. The entire process is wrapped up in one DO Loop. Anyone interested, let me know, I've already been through the pain of multiple paths down the wrong road on this project and I'm finally happy with how it turned out. Just don't attempt it without using an SX or better (you need the speed of the faster stamps).
  • kwinnkwinn Posts: 8,697
    Did you notice that this thread was started 12 years ago?
  • truetechtruetech Posts: 6
    Yes, Just wanted to share my experience with other users
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