What happened to Altimeter V4 (Strange Behavior!..) - RC Groups
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Jan 23, 2013, 09:46 PM
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What happened to Altimeter V4 (Strange Behavior!..)

Well, I recently upgraded to V4 Altimeter. I made one test flight and the result was above my expectations. I praised the V4 in the original Altimeter V4 thread (just about a week ago).
Today, I did my second flight with the new V4 Altimeter on board my hexacopter.
I am climbing straight up on a clear afternoon. Temps are in low 70s (very dry conditions).
All of a sudden I get a voice alert from my OSD system. The max altitude (400 feet) exceeded. I look at the reading and it shows over 600 feet!!! WHAT?
I am confused!.. Then it corrects itself. I am at 100 feet. I climb to 150 feet and stop there. It shows 150feet (-/+ 2 feet) very acceptable. I am just thinking that it was probably the sudden environment change (from my car to outside). I didn't wait much for the sensor to get adjusted to outside conditions.
So in about 10 seconds, the altitude reading jumps back up to 350feet. I land and it reads 200+ while on the ground.
I reset the OSD. It starts at 0 and does the same thing again. Worse than Altimeter V3!!! What the heck...
I stop flying and trying to understand what causes this. I do a few more resets. Nothing changes. It starts at zero feet every time; It is consistent for a few second and then jumps 20-30 even 50feet while I am holding the multi in my hands (No motors are running) So I know it is not about interference.
Then all of a sudden, I realize the sun light hitting the sensor directly from the Horizon. It is a sunset time; and the Sunlight hitting the sensor from the side. I mounted the sensor so that the single-digit screen is facing sideways.
As soon as Sunlight hits the sensor, altitude reading jumps; when I cover it with my hands it goes back to normal.
I then cover the sensor with an electrical tape; fly and sensor functions as expected.
The reason why it fixed itself all of a sudden during the first take off was that I was rotating. And at the moment sensor turned away from the sunlight.
The other day when I did my first test flight, it was after the sunset (almost in dark). So that's why it didn't happen. So I am pretty sure the cause is the sunlight.

Is this a KNOWN issue with this sensor? How? why? Reason!..

Should I change my mounting position or cover the sensor?

Bill, hopefully you will read this soon
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Jan 26, 2013, 04:47 PM
billpa's Avatar
Hi Iskoos,

Sorry for the trouble. We have had a couple of reports over the years of the sensor element responding like that to direct sunlight (but I don't recall movement of that amount), which is generally only an issue for multirotors, where it is mounted outside the fuselage. Any mems based barometric sensor will likely have the same issue.

The solution is exactly what you described - covering it should completely eliminate it.

I have just updated the installation and troubleshooting sections of the manual to reference this possibility, as more and more people use the sensor in multis.

We're going to be adding a light shield to the sensor in future production runs to make sure no one else is confused by this.
Jan 27, 2013, 11:43 PM
Registered User
That's great that you guys listen to us and make the necessary modification. Good customer service...
Actually when I was saying it jumped from 150 to 350, I was being very conservative. Yesterday I playedback the recorder file and it actually jumps from around 100 feet to over 600 feet in a matter of few seconds and the altitude was unstable throughout the flight.
I remounted the sensor so it is now facing down. I removed the covering to see how it will work. I did two test flights; One was yesterday, sensor worked flawlessly but the flight took place after the sunset. So it shouldn't say much. Today I did the second one right afternoon and it worked okay as well. I will do a few more tests and if I see no problem, I will not cover the sensor.
But let me ask, if I need to cover it, can I use aluminum foil? And should I leave any opening so the sensor element can have direct air path?
Jan 28, 2013, 10:00 PM
billpa's Avatar
I suspect there may be some variability from sensor to sensor re direct sunlight sensitivity.

We are determining how best to cover the sensor itself it in production.

If you are removing the shrink covering on the altimeter, one way to completely block the sensor from light is to cover the element with electrical tape, but put a small square of paper (slightly bigger than the hole(s) in the sensor element) on the sticky side of the tape, to keep the adhesive in the tape from directly contacting the holes. Those holes should not be completely blocked by adhesive.
May 09, 2013, 10:56 AM
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MJB9's Avatar

Can you post a picture of how to correctly cover the ALTIMETER-V4? I am about to buy one and want to do the mod correctly.
May 09, 2013, 04:42 PM
billpa's Avatar
Hi, if this is inside a plane and not exposed to direct sunlight, I suspect this will not be an issue for you. If you are using it where it will be directly exposed, I would first just place a small piece of black electrical tape directly above the sensor (small rectangular white or metal sensor shown in the photo here), without removing the heatshrink casing from the altimeter.
May 09, 2013, 04:51 PM
Registered User
MJB9's Avatar
Thanks. It will be inside a quad, but there are openings all around it so I definitely will want to shield it. Any issues with just replacing the clear shrink wrap with black shrink wrap? I don't need the display showing since I'll be using OSD Pro.
May 09, 2013, 04:59 PM
billpa's Avatar
There is no issue with replacing the shrinkwrap. However, you might want to try it as-is first, to see if this is even necessary. The sun induced drift seems to be very rare.
May 09, 2013, 05:15 PM
Registered User
MJB9's Avatar
Will do--thanks. It's not like it will be same issue with naza m where it could shoot up/down and crash because of this. I'll only be using for altitude checking and not part of guardian suite.
Jun 17, 2013, 09:01 AM
Registered User
I just purchased a V4 from Tower. It seems to have an extreme sun light sensitivity. Reading thousands of feet instead of hundreds. I bought it to see how far up I was going in auto's with a TREX 600. It is mounted on the rear gyro spot. The first one or two seem to read correctly but then it goes completely nuts. I put a towel over the heli between flights. Black tape seemed to work but I need more flights to verify this - ran out of battery.

My question is whether the sensor is sensitive to sun light ? or is it just getting hot ? from the nice green house formed by the clear shrink. I would be dazed and confused if the sensor is actually sensitive to light.
Jun 19, 2013, 01:18 PM
billpa's Avatar
Four Stroker, sorry to hear about the issue. There seems to be variability from sensor to sensor regarding sunlight. We occasionally hear reports of massive variation, but they are not typical. Covering the sensor with black tape should take care of it.
Jun 29, 2013, 05:47 PM
Registered User
I removed the shrink wrap and made a black plastic cover for the sensor from frozen dinner tray. Put clear shrink back on. It now works as expected.

I had to go find out why a MEMS pressure sensor was light sensitive. The ones made with a silicon membrane are - light solar cells. Other technologies are not.
Oct 14, 2013, 07:20 PM
Registered User
I have the V4 Altimeter that is displaying erratically do you think that tape would help?
Oct 16, 2013, 09:10 AM
JohnET's Avatar
It is possible. Give it a try and if it doesn't help, open a support ticket and we will get it sorted.

Regards, John

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