Slow speed boat speedometer, for a row boat.

Discussion in 'The Projects Forum' started by bundick, Aug 4, 2010.

  1. bundick

    Thread Starter Active Member

    Dec 19, 2007
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    I row when I fish. No motor of any kind.
    I'd like to know how fast I'm rowing.
    This Speedometer would have a Digital .7" LED read out. Two of them, for miles and tenths/per hour.
    I don't think I can row any faster than 9 Mph :D

    In the past there have been Boat speedometers which were a little paddle wheel, moved by the water, an inductor to read the blades on the paddle wheel.

    Then what?
    I'm sure it's something I can put together. On this site there are Schematics to read counters like that and also to put the output to an LED display.
    This is going to be a 12Vdc or less device.

    If someone can make up a Block diagram, or link to them, I may be able to do the rest.:rolleyes:
     
  2. tom66

    Senior Member

    May 9, 2009
    2,613
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    A simple configuration would be a LM2917 (frequency to voltage converter) and an ADC chip. You can even buy a panel meter to read a voltage, then set up the LM2917 to output how you want. Or you could use a PIC microcontroller or similar microcontroller to time the pulses and output a speed. You would need some way of calibrating it, if you used a GPS device to give you a reference that could work.
     
  3. bundick

    Thread Starter Active Member

    Dec 19, 2007
    97
    1
    Thanks Tom. The microcontroller is way too much for me. Is there a way to make an analog circuit to read the pulses into the LM2917?
    Then send the out put of the counter to a pair of LED?
     
  4. tom66

    Senior Member

    May 9, 2009
    2,613
    213
    An LM2917 converts a frequency to a voltage. There's an application note for a rev-counter based on this IC. One thing is, the output will need to be adjusted to give MPH or knots or whatever you want. I designed a tachometer for my model plane (to measure the RPMs of the motor) based around one of these chips, so I have some experience with this chip - let me know if you need any help.
     
  5. bundick

    Thread Starter Active Member

    Dec 19, 2007
    97
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    OK, that's a start for me. Thanks a lot.
    Freq of the little paddle, converted to a voltage, moving the needle of a volt meter would be the simplest thing (I'm guessing)
    Then all I'd need is a small LED to light the display. Cool!
     
  6. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
    92
    I hope it isn't too against the intent to suggest a few more options.

    Several types of GPS including certain GPS equipped phones with the right apps can be set up to log your speed.

    If knowing your speed is the real requirement then that is going to be a good option.

    If you just want to make a speedo project then consider using a GPS system when you need something to calibrate against.
     
  7. Potato Pudding

    Well-Known Member

    Jun 11, 2010
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    I also meant to suggest a MEMS accelerometer based velocimeter.

    A paddlewheel based device is going to be better for measuring wave action than it will for your forward rate of speed.

    MEMS based accelerometers are not too horribly expensive in fact they are at the price range where they have become disposable. They are used in tell tales that are can be included in packaging for fragile high value equipment to log via a microprocessor, all the shocks from drops and rough treatment that the package suffers during shipment. They are also used in Laptops to detect freefall and park the hard drive in case the laptop is dropped. They are in the sensors that tell airbags to deploy. They are becoming very common because they are so useful.

    They work on the capacitance changes on cantilever nanostructures that are springy and bend when they are under acceleration. That means that they are simpler than you might have imagined to use.
     
  8. bundick

    Thread Starter Active Member

    Dec 19, 2007
    97
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    Thanks Pudding.
    RE: that fancy stuff; Your talking to the village idiot. I can just barely handle analog circuits. I'm not the guy to go delving into Micro Processing circuits.

    So far I'm up to the point where I'll have the little paddles, with magnets or Steele implants, and an inductor looking at those paddles as they go by.
    Then I'll amplify the "bump" and feed it into a frequency to voltage circuit and fee that into a Volt meter. I'll put a small LED in the panel meter to light it up for me.

    I do intend to use the GPS to verify my speeds and mark the panel meter with the speeds.

    I thank you a bunch for trying to enhance my effort.
     
  9. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
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    Analog Output

    That is one of the ways that it can be kept retro if you went with the Accellerometer. It just gives you a voltage out.

    Some Op Amps and a Panel meter and you are done.
    From the Op Amps you want a buffer and an integrator.

    Scrounge an analog panel meter. You can buy cheap needle and dial multimeters for a few dollars for example and scrap them to salvage the meter. You can open it up and relabel the dial with the speed.

    The whole thing could work on two AA batteries.

    I will try to resist further suggestions now that I have said my bit.
     
  10. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
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    If you're not really concerned about accuracy find some sort of small DC motor that's sealed so it can be immersed under water and attach a tiny propeller to the shaft. Since it's being driven the DC motor will act as a generator supplying an output voltage that rises as the shaft speed increases.

    As to a readout why not just buy one of those $5 digital panel meters off eBay? Must be a couple dozen people selling them on there in all sorts of ranges for next to nothing, you just have to put up with about a 10 day wait for China airmail to get here.

    I use quite a few of them in various projects, the latest ones I bought are even programmable such that you can have a 0 - 10 VDC input display as about any range indication you want. They come with a tiny programming interface board and some cables, a simple program you download is used to program them. The only downside is they don't have the decimal point feature in the program yet.

    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=370326104110&ssPageName=STRK:MEWAX:IT

    Might be overkill for your project though. I'm guessing a common 6V DC motor from an old CD player, wrapped in tape then sealed with silicone seal might do the trick. Experimenting with the size and pitch of the tiny pickup prop could probably net you a 0 - 2V output which, with the proper cheap meter, could be made to display as 00.0 - 19.9
     
  11. bundick

    Thread Starter Active Member

    Dec 19, 2007
    97
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    Those are all good suggestions. Thanks. I like the Red LED style panel meter design too. Just the thing for the dark of night.

    PS: I think the first accelerometer I was introduced to had a moving part inside a package. I think it was a Piezoelectric device.

    I envisioned it sorta like an earthquake monitor. A dangley that would touch a wire ring and make contact.
     
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