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Cycle Computer Sensor

P

pandy

Jan 1, 1970
0
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?
 
P

Paul Hovnanian P.E.

Jan 1, 1970
0
pandy said:
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?

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.
 
R

Robert Roland

Jan 1, 1970
0
The commersial cycle computer product such as VETTA and Sigma
have every long usage time in a lifte of CR1023 battery.

I have a Sigma on my motorcycle. It uses a reed switch.
Is reed switch stable enough for cycle computer

I'd say they are. The switch is, of course, wrapped in sturdy plastic.
( they of cause do
not
satisfy for speed sensor in a car)?

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.
 
P

pandy

Jan 1, 1970
0
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.
 
D

Dave

Jan 1, 1970
0
pandy said:
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
 
T

Tony Williams

Jan 1, 1970
0
Dave said:
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.

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.
 
P

pandy

Jan 1, 1970
0
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.
Very useful advices.
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 ...

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?
 
P

pandy

Jan 1, 1970
0
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.
 
T

Tony Williams

Jan 1, 1970
0
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) = <5mA max contact current.

R2 = 20*R1... giving Logic 0 = V+/21.

With those numbers, and a 5v rail.

Closing time will be roughly 1.3mS from 5v to 0.25v.
Opening time will be about 30mS from 0 to 3v.
Max frequency up to about 32Hz.
 
P

pandy

Jan 1, 1970
0
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 intensity the
reed switch
needs.
 
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