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Old 04-05-2009, 01:58 PM
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Earthman Earthman is offline
Motorized Bicycle Senior Member
Join Date: Mar 2009
Location: Pittsburgh, PA
Posts: 82
Default Speedometer problem from RFI or EMI.

I just installed a cheap, 4-function electronic bike speedometer that mounts to the handlebars of my bike (I wanted to know how fast I was going). After setting up the meter and starting the engine, I found that electronic noise from the ignition system caused the new meter to malfunction by going into reset mode. As long as the engine was running, the meter would not work.

The fix was to install a small split ferrite bead on the sensor wire between the magnetic sensor and the meter (see photos). These things are made to suppress RFI (radio frequency interference) in electronic equipment. They are inexpensive and easy to install. I just happened to have a bunch handy, snapped one on, and solved the problem. Since I’m an amateur radio operator, a.k.a. HAM, I tend to accumulate such stuff.

If you have similar problems, but don’t have a split ferrite bead handy and don’t know a HAM, you might be able to find one at Radioshack or online. Buy from the following links:

Digi-Key - 240-2344-ND (Steward - 28A0434-0A2)

The link above is for Digi-Key Part Number240-2344-ND



More info on RFI suppression can be found at …

Ferrite Beads
Attached Images
File Type: jpg CIMG8447.JPG (644.7 KB, 210 views)
File Type: jpg CIMG8446.JPG (648.2 KB, 212 views)

Last edited by Earthman; 04-07-2009 at 08:03 PM.
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