Teardown: Dashcam GPS antenna

Article By : Brian Dipert

Successful teardown reversals open the doors to subsequent dissections of location-sensing accessories.

After having torn down and subsequently successfully reassembled two Aukey dashcams, the DRA1 and (more recently) DRA5, I had two options for what to do with them: donate them or keep them (I guess I could also “sell them”, but that’d really stretch the meaning of “open box”, wouldn’t it?). So far, I’ve kept them. And in preparation for potentially pressing them into service, I’ve purchased two accessories for each:

I ordered three of the latter, actually motivated in part by a quantity discount offer from the seller, and with a teardown in mind.

These modestly priced devices (currently listed on eBay for $8.99 each) are more than just passive antennas; they include processing ICs that merge and reconcile the signals coming from multiple GPS satellites and output a serial data stream (strictly speaking, in the form of NEMA sentences) that informs the dashcam of its real-time location for display, datalogging to a SD card, etc. In fact, modern receiver ICs are instead referred to as GNSS (global navigation satellite system) devices because they comprehend not only GPS but also Galileo, GLONASS and other services. Maxim Integrated’s (now Analog Devices’) MAX7269 is a representative example.

My unit arrived absent any instructions and packaged only in a clear plastic bag.

Here’s what it looks like unbagged, as-usual, alongside a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes:

You’d be understandably confused if you looked at the connector and wondered if the GPS receiver outputs stereo audio (or to be exact, in this particular case, acts as a stereo headset with an additional mono microphone output, or as a balanced-input headset). It certainly looks like a conventional 3.5mm audio plug, doesn’t it? Scan GPS receivers on eBay or elsewhere and you’ll find both four- (TRRS) and three- (TRS) conductor versions; I needed to be sure that I bought the variant expected by the Aukey dashcams…but hold that thought.

Sometimes in these teardown projects identifying the components once I get inside is the biggest challenge. And other times, just getting inside is the hardest part. This was one of those latter situations, as it turned out. But I’m getting ahead of myself. Step one was to peel off the sticker on the bottom of the receiver, which revealed a coin-shaped magnet underneath, presumably intended to “stick” the receiver to a piece of metal on the inside of the vehicle (again, I’m somewhat guessing, because….no documentation…):

But all that sticker peeling didn’t actually get me inside. So, my attention was next drawn to a seam around the sides of the receiver:

The seam was asymmetrical (horizontal on two sides, curved on the others), so I was skeptical that it was anything more than cosmetic, but I figured it wouldn’t hurt to try anyway…

I’m not like other, luckier folks with their fancy, pricey sonic blades ;-), so I as-usual had to resort to box cutters and screwdrivers-as-chisels (I almost also broke out the hacksaw):

When the side-seam attention didn’t get me anywhere (I was at the time operating under the eventually-incorrect assumption that the top part of the case was snapped or glued to the remainder and would eventually yield), I turned my attention to the bottom-side circumference seam; which you can, in retrospect, faintly see in the earlier photos after I removed the sticker:

But no matter how much of the outer case I was able to break away, and how long I applied a heat gun to the assemblage, I couldn’t get that top off:

Taking a breather, I peered inside and saw another seam:

Redirecting my implements-of-destruction attention to it got me where I wanted to be:

Turns out, my screwdriver jabbing had inadvertently also jostled the Faraday cage inside loose (along with creating other damage which you’ll shortly see, but none to me, thankfully):

The PCB lifted right out:

Revealing…well, not much, unless you’re into low-noise amplifiers. Specifically, there are two SOT-23-6 packaged AT2659S devices from a company called Zhongkewei, and alternate-sourced (Google informed me) by Maxim Integrated/Analog Devices. What about those scoring marks on the PCB, by the way (such as the ones on either side of component F1)? Those were from my screwdriver and the neanderthal who was wielding it.

Flip the PCB over and you see a squarish device attached to the other side, a ceramic patch antenna to be precise:

All of which leaves me with two questions:

  1. Where’s the GPS receiver chip? No matter what I tried, I couldn’t get the ceramic patch antenna to budge, so I can only assume this particular IC is mounted on the non-visible side of the PCB, in-between the PCB and the antenna.
  2. Why was a four-conductor plug necessary? Look closely at the soldered connections between the wire and the PCB and tell me how many you count. Three, right? Which makes sense…power and ground coming from the dashcam, plus serial data headed to the dashcam. If this were an A-GPS design, where the receiver’s GPS-sourced location data is augmented by cellular tower-sourced location data coming either from the dashcam itself or (for example) a cellphone Bluetooth-connected to the dashcam, a fourth wire (and conductor mated to it) carrying a serial data stream headed in the opposite direction might make sense, but that’s not the case here.

That all said, and as I’ve admitted before, RF stuff isn’t my particular forte…therefore why I count on my readers to fill in the knowledge gaps. Sound off in the comments, please!

 

This article was originally published on EDN.

Brian Dipert is the Editor-in-Chief of the Edge AI and Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.

 

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