|   strange cyclocomputer problem -- going nuts!!! | rp
May 21, 2003 9:30 AM | | I've got a Cateye Mity 3 on my bike. It "clicks" everytime the spoke magnet passes by the fork sensor. I've checked everything -- nothing is hitting. The noise disappears when I move the magnet down the spoke out of the sensor's range. Has anyone ever heard of this? It's driving me crazy! |
| it's normal, | More than likely
May 21, 2003 9:36 AM | | |
| relays click when magnets pass by. It's made that way. sm. | clary.
May 21, 2003 9:46 AM | | Secret message: get used to it. |
| It didn't always do this though... | rp
May 21, 2003 9:50 AM | | ...at least not that I could hear. I've had other computers (even cheaper ones than this cheapie) that made no audible noises. ARGHH!!!! |
| The noise is always there | shiggy
May 21, 2003 9:57 AM | | Just easier to hear sometimes |
| Get a quiet Avocet computer then...it uses a coil rather than a relay... | clary.
May 21, 2003 10:04 AM | | Avocet computers
The better models of Avocet computers work on a different principle from all others. The Avocet sensor is not a magnetic switch, but a coil of wire. As the 20-pole magnet ring rotates past the coil in the sensor, a small electric current is generated. You can test this with an AC voltmeter. Spinning the wheel by hand, you should be able to measure an AC voltage of around 50 millivolts at the handlebar terminals. If you test with a continuity tester or ohmmeter, you should get continuity regardless of magnet position. Unlike most cyclecomputers, the Avocet system allows you to replace just the wire, without replacing the sensor or the handlebar mount.
(The Avocet models 15 and 25 use conventional reed switches with single spoke magnets.)
http://www.sheldonbrown.com/cyclecomputer-troubleshoot.html#avocet_computers
Will the real Sheldon Brown please stand up! ("On May 5, 2003 I shaved for the first time since 1968.")
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| relays? | pimpbot
May 21, 2003 11:49 PM | | Relays typically use a lot of power (compared to solid state switching, like transistors, no moving parts!) to actuate. I would be surprised to see one in a speedo that ran of a lithium calculator battery... it would have to draw so much current that the battery would die in a few days of use. Relays are't needed in devices like these since MOSFET transisitors with their ultra high impedance have been invented. That's why a typical bike computer can run for a year or three off a tiny battery. Every system I've seen uses a magnet on the wheel to generate a tiny signal in a humbucking coil of wire attached to the frame or fork. There are no moving parts in the pickup mechanism.
The clicking may be some kind of mechanical shifting on your wheel magnet. Try zip tying it down to your spokes to see if it goes away. |
| <font color=red>R E L A Y !</font> A computer sensor is a magnetic reed relay switch... | clary.
May 22, 2003 6:56 AM | | "a switch is classified as a relay when it incorporates electrical contacts".
A proximity switch, activated either by an electromagnet (coil) or a permanent magnet, is most often classified as a relay when it incorporates electrical contacts. The general concept is that a switching action takes place without any physical contact.The reed relay hermetically sealed in a glass envelope is a classical example of a static magnetic proximity switch. Most references to it may be found in literature related to relays.
http://www.geocities.com/ResearchTriangle/Thinktank/4347/Proximity_Switch/proximity_switch.html
What is a reed switch ?
The basic reed switch consists of two identical flattened ferromagnetic reeds, sealed in a dry inert-gas atmosphere within a glass capsule, thereby protecting the contact from contamination. The reeds are sealed in the capsule in cantilever form so that their free ends overlap and are separated by a small air gap.
How does a reed switch work ?
When a magnetic force is generated parallel to the reed switch, the reeds become flux carriers in the magnetic circuit. The overlapping ends of the reeds become opposite magnetic poles, which attract each other. If the magnetic force between the poles is strong enough to overcome the restoring force of the reeds, the reeds will be drawn together.
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| And don't forget... | pimpbot
May 21, 2003 11:55 PM | | DC electric current flows from negative to positive, not the other way around as commonly believed.
I know it's not relivant here, I just wanted to start a flame war. It's true though!
Negative means that there is an excess of electrons, and positive is a deficit of electrons. Which way do you thing the electrons wanna go?
Of course, AC flows both ways, it switched direction all the time. |
| Where were you when Steve Fossett needed hot air? | clary.
May 22, 2003 7:03 AM | | |
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