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Cycle Computer Sensor

From the information I search from internet, Cycle computer sensor used in the real world may fall into three catalogs: reed switch or Hall effect sensor, or Magnetic Resistor.

Reed switch seems a mechanical switch that can switch on when magnet comes and off when it goes.

Reed switch ++ advantage: simple, easy to interface to circuit, no power consumed.Only two-wire need to interfaced to circuit.

Hall-Effect Sensor: ++ advantage: more stable, long life, electrical(not mechanical), Can change three wires to two wire interface. accept higher frequency detecting. ++ disadvantage: Comsume more power.

Known little about another one : magnetic resistor.

It is difficult to choose one from these three kinds. I wonder which kind the industry adopt.

The commersial cycle computer product such as VETTA and Sigma have every long usage time in a lifte of CR1023 battery. If they use Hall-Effect sensor, (since Hall-Effect sensor consume much current) how can they reduce power comsumption?

Is reed switch stable enough for cycle computer ( they of cause do not satisfy for speed sensor in a car)?

Which is the best choice?

Reply to
pandy
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Number 3: The coil pickup. Its simple and requires no power to the sensor and it has no moving parts.

By the way, I have a 1979 Porsche which uses a reed switch pickup for the speedometer. 160,000 miles and it still works.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
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Life is like a buffet. Its not very good but there\'s plenty of it.
Reply to
Paul Hovnanian P.E.

I have a Sigma on my motorcycle. It uses a reed switch.

I'd say they are. The switch is, of course, wrapped in sturdy plastic.

An inductive pickup is probably more reliable, and in a car, power consumption is no real issue. It also has the advantage that you can use an existing sprocket as input.

On the other hand, the reed switch works well on bikes and motorcycles, so I'd think it would work on a car as well.

--
RoRo
Reply to
Robert Roland

Robert Roland, Paul Hovnanian P.E: Thank you very much.

I am now convinced that reed switch is a good choice in a cycle computer.

I am now searching a small reed switch that can fit cycle computer's requirement.

Reply to
pandy

A key point in obtaining a long life from a reed switch is not over driving it with too strong a magnetic field - aim for something like 25 - 50% over 'just operate'. Stronger fields will tend to cause early failure from fatigue.

Also note that the contacts that stick out of the reed switch are part of the magnetic circuit - if you cut them down or bend them the sensitivity will drop substantially - hence the smallest reed switch may not be a good choice ...

Dave

Reply to
Dave

The other key to reed switches is to limit the current/voltage, and the ambush most people fall into is to have a capacitive load. Best life is obtained with a limiting resistor, mounted as close to the switch as possible.

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Tony Williams.
Reply to
Tony Williams

Very useful advices.

Then, we should average the size and the sensitivity of the reed switch. Lots of test may be done to achieve a good selection! Has we have any experiential point?

Reply to
pandy

A limiting resistor is needed for longer life for a reed switch also for the longer life for one battery lifecycle. Any further suggestions are appreciated.

Reply to
pandy

-------------------------------------------------------- Bad. _____V+ ~~~~ | [R1] +------------------------------------+--->uP Reed / Line, C and L. | +-------------------------------+ ===C1 | | +----+--->0v

-------------------------------------------------------- Better. _____V+ ~~~~~~~ | [R1] +-----------------------------[R2]---+--->uP Reed / Line, C and L. | +-------------------------------+ ===C1 | | +----+--->0v

-------------------------------------------------------- Best. _____V+ ~~~~~ | [R1] +-[R2]-------------------------------+--->uP Reed / Line, C and L. | +-------------------------------+ ===C1 | | +----+--->0v

--------------------------------------------------------

Very roughly, and depending on logic input requirements.

R2*C1 = 1 mS..... filtering closing contact bounce time.

V+/(R1+R2) =

Reply to
Tony Williams

I am studying Model RI-02, Ri-01C, RI-70, RI-90 of COTO company.

They are all small enough. it seems one of which can satisfy the requirement.

The next step will be choosing a proper magnet for the cycle computer.

I will refer some document to caculate of the magnetic > >

Reply to
pandy

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