View Single Post
Old Nov 11, 2011, 01:59 PM
Tom Frank is online now
Find More Posts by Tom Frank
Dance the skies...
Tom Frank's Avatar
United States, MA, Walpole
Joined Dec 2003
19,007 Posts
Originally Posted by gblackford View Post
Thanks for the great post and especially the user manual. It beats the heck out of trying to decipher english as written by a Chinese person.
I just received the newest 808 camera that I ordered from eletoponline365. Service was faster than expected and camera works great (no date and time stamp). I also tested out in car video and definetly had EMI static from the engine. As an experiment I wrapped the camera in aluminum foil. Eliminated the EMI, but I'm worried about the heat being trapped. Maybe construct some sort of small aluminum box to shield the camera from EMI? Just thought I'd let you know.
Well first, the excellent user guide credit goes to Isoprop for writing it! I merely linked it in the FAQs.

The static noise heard in the video is, I think, as suggested by timetec in another post, not EMI but rather an audio clipping cause by the VERY low frequency response of the sound pickup (an electret mic, I think?). The very low rumble from road noise (which we can't hear very well) is easily picked up by the mic, and its amplitude drives the mic into clipping, which we CAN hear as static.

I first thought it was EMI as well, because the static stopped while driving when the car stopped with the motor idling, then started again when the engine speed picked up as I began moving again. But after reading about the clipping, I did another test while not moving, reving the engine to different rpm, and I had no static whatsoever. I thought it might be coming in through the car charger cable which I used during my driving test, so I connected that and still no static at different motor speeds. I also did a driving test with no cable connected, and the static started again when driving. So that convinced me it was the electret clipping and not EMI.

There was a possible camera hack fix suggested in timetec's post which might solve the problem (a different capacitor in the mic circuit) but there's been on posts showing a hack which confirms this. I thought I had given a link to this in the FAQs, but it appears I forgot. I will fix that now, so thanks for your post.

You can do testing similar to what I did to see if it's also mic clipping causing your static. Perhaps your foil shielding is attenuating the road noise enough to prevent clipping? If not, let us know.
Tom Frank is online now Find More Posts by Tom Frank
Last edited by Tom Frank; Nov 11, 2011 at 02:34 PM. Reason: hack was suggested, but not yet done.