Cycle Computer Sensor

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.

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.

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.

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

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.

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?

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.

-------------------------------------------------------- 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) =

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 > >