Electronics, Lighting, & Gadgets - VDO cumulative altitude malfuctions

This is an interesting puzzle. My friend has 2 VDO MC1 cycle computers. They both work perfectly, except that erratically, in mid ride, the "altitude gained" number goes haywire -- on each of them! Every other calculation on his computers is correct for the entire ride -- mileage, speed, % grade, even the "real altitude."

Today at the coffee stop we examined each of our computers (I have the same computer on my bike.). The only difference we could note was that his is mounted on his stem, so there is chrome right beneath the hole on the underside of his computer, while mine is mounted on the handlebar. Could the chrome, a half-inch or so underneath the little hole, have an effect on the perceived altitude gained?

We thought perhaps his computer was simply malfunctioning, but when he put an identical brand new one on the same bike, the same thing started to happen.

Any ideas?

Are they wireless? Perhaps there is some sort of electrical interference.

Yes, they are wireless. But mine never malfunctions when we're on the same ride.

Yes, they are wireless. But mine never malfunctions when we're on the same ride.

Who knows, maybe something in his bike or the placement of his mount is amplifying some electrical noise. Have you tried swapping computers with him when the malfunction happens?

No, we'll have to try that. It certainly seems to have something to do with his own configuration, since 2 identical VDO's do the same thing on his bike.

One thing just occurred to me. In addition to the VDO on his stem, he has a Flight Deck on his handlebars. He added the VDO on his stem because the Flight Deck doesn't have the altitude. I wonder if the Flight Deck is providing some kind of intermittent interference?

No, we'll have to try that. It certainly seems to have something to do with his own configuration, since 2 identical VDO's do the same thing on his bike.

One thing just occurred to me. In addition to the VDO on his stem, he has a Flight Deck on his handlebars. He added the VDO on his stem because the Flight Deck doesn't have the altitude. I wonder if the Flight Deck is providing some kind of intermittent interference?

That sounds very likely. Maybe try turning off the Flight Deck when the VDO is going wonky to see if it stops acting up.

Thanks. We'll have a pretty long ride together on Saturday and I'll suggest he remove the Flight Deck and see how it behaves.

Success! When he put the VDO on his other bike, without the Flight Deck, it worked fine for the whole ride. The 2 sensors are most likely interfering with one another, similar to what happens when 2 Polar Heart Rate Monitors are in close proximity.

Thanks for the suggestion about "electrical interference." That's what made me think about his Flight Deck.

Success! When he put the VDO on his other bike, without the Flight Deck, it worked fine for the whole ride. The 2 sensors are most likely interfering with one another, similar to what happens when 2 Polar Heart Rate Monitors are in close proximity.

Thanks for the suggestion about "electrical interference." That's what made me think about his Flight Deck.

Excellent! Glad you got it sorted.