I have a long-time friend and colleague, Bob Diamond, Department Head, Mechanical Engineering at L3 Narda-MITEQ on Long Island, NY. We worked together in the 80s at General Microwave Corp. in NY---Bob was a mechanical engineer and I was an analog and power engineer there at that time. We’ve both come a long way in 35 years.
Here is Bob’s brief description of his recent addition to his car with a dashcam and some subsequent problems he encountered with noise on his AM Radio:
My daily commute is about 12 miles each way from Babylon to Hauppague and back. The best North-South route for me is using the Sagtikos Parkway most of the way. The Sagtikos Parkway goes North and South in an almost perfect straight line for over 10 miles. Many drivers on this road think they can go near 90 MPH until they end up crashing into the car in front or alongside them. It is one of the most accident-prone routes on Long Island.
In my near 20 years of driving this road I have never had an accident but I‘ve had a few close calls and have seen an un-countable number of accidents. Because of this, I thought it would be a good idea to install a dashcam on my car; God forbid I get caught up in an accident or a witness to one. Plus, I enjoy doing ‘mods’ to my car and playing with electronic toys! (Editor Steve T: “I love when ‘Mechanical guys’ do electronics/electrical DIY projects! Bob is a very versatile engineer; you can be sure I will be calling on him when I run into any mechanical challenges in my projects.)
Because of the above, I bought a mid-dollar range dashcam and mounted it on my windshield. The power supply for the dashcam has a mini USB plug at the dash cam end and a power plug (cigarette lighter plug) at the other end. I didn’t like the wire hanging down from the cam, across my dashboard and into the power receptacle. When I do mods to a car, I want it to look factory installed.
After some internet research, I found a company called ‘The DashCam Store’ that sells hard-wired power supplies for Dashcams. You run the wire from the Dashcam up and under the headliner, down and under the pillar trim, and then down into the fuse panel. The kit includes a DC-DC converter (see Figure 1) that you plug into the fuse panel and chassis ground. This all becomes hidden inside the fuse panel area.
The power supply that came with the DashCam
Even though I have a great sound system in my car, plus satellite radio, I still listen to AM radio quite often for news, traffic and weather. I normally listen to WCBS AM, which is 880 on the AM dial. WCBS is a 50,000 Watt clear-channel broadcast station. As soon as I installed the Dashcam kit, all of my AM reception was wiped out by interference from the Dashcam DC-DC converter. I tried a direct ground to the battery, shielding the DC-DC converter in a metal box and a Mu-Metal box with no improvement. I also tried re-routing the wires and shielding the wires, also with no improvement. At that point I contacted Steve Taranovich, knowing that ‘Mr. Analog’ would most likely know of a solution.
He was kind enough to direct me to Linear Technology and they supplied me with their LT8645S Step-Down Silent Switcher test board as Steve recommended.
I bought a plastic electronics project box and mounted the board in the box (see Figure 2).
The Linear Technology LT8645S demo board which solved the noise problem.
Then I simply cut the input and output wires off the DashCam Store DC-DC converter and soldered them to the LT8645S board. Before I closed everything up I started the car, turned on WCBS 880 AM and Voila!--- ZERO interference, crystal clear AM reception. I scanned up and down the entire AM band and all is crystal clear. It works perfectly!
Editor Steve T: I love a story with a happy ending. See my review of this Linear Tech power solution on EDN, Silence is golden: 65V, 8A synchronous step-down switching regulator.