Need Help Identifying PCB Design Feature

[Travman1023]

Hello,

I am looking at a steering angle sensor that has a printed circuit board with this wheel-shaped array of copper pads (see image). I am trying to get more info on how and why it works, but I don't know what this thing is called. Is it a capacitor? A switch? Or is it for a coil inductor? There wasn't any components or parts above it so I am thinking it might be for a different application or obsolete tech. I am an ME so my EE knowledge is limited. Thanks for any tips or feedback!

 

[IRstuff]

Maybe just an Easter egg

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[Compositepro]

I'm guessing that it is a schematic diagram of the printed circuit. There is no added cost to doing it this way since the circuit itself must be printed.

 

[MacGyverS2000]

Normally I would say it's a rotary encoder or multi-position rotary switch (one connection at center spoke, second connection to multiple possible paths, 2/3rds of which don't connect to anything), but the schematic-looking capacitor marks have me seriously scratching me head. Can we see an overall pic of the entire board (and maybe something in the pic for scale, like a quarter or a ruler)?

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[IRstuff]

The OP said there weren't any components in that area, and there are no vias nor sufficient solder pads for the "capacitors"

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[MacGyverS2000]

Yeah, I only see two vias, and the capacitors I mentioned are schematic symbols for caps, not actual component sites... I'd still like to see the entire board to try and get a better feel for why that stuff might be there.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[IRstuff]

No, I got that, but neither "capacitor" shows no vias at the circular thing side that could lead to a component mounting location. Those ends are completely floating.

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[Travman1023]

there is the backside.

I.D. of PCB is 1.5in
O.D. of PCB is 3.0in

most right pad (#1) is Vcc 5.0V
Pad #2 is GND

thank you for the comments/direction

-T

 

[IRstuff]

seems oddly unbusy, compared to below. What vehicle is it from?

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[Comcokid]

Just a guess. It looks like the encoder is based on a capacitance sensing method. There are four outer tracks of encoding plus one inner track of (possible) zero index. It looks like the PCB feature circles on an area where there are no tracks. So my guess would be that this PCB feature is a reference capacitance to determine the gap to the metal index ring to get additional accuracy for the encoding. The capacitor symbol-like traces may be there to determine the PCB dielectric constant for calibration/test of stuffed PCB before final assembly as an encoder. With a stuffed PCB w/o encoder ring calibration they can adjust for variations in the PCB dielectric constant variations lot-to-lot. And if they're really clever, the PCB feature can also help compensate for the capacitance change in the field as the PCB moisture content varies due to seasons, temperature, or relative humidity.

 

[MacGyverS2000]

Agreed, Comco... now that I can see the entire board, the feature being asked about is only indirectly related to the overall operation (aka, it has to be some form of reference, either once after initial install, maybe once during each ignition cycle).

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[IRstuff]

Still think it's an Easter egg; note that 3 of the 4 "connections" are actually floating and don't go anywhere.

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[MacGyverS2000]

Depends upon what sits above it... that's a good way to make a capacitive plate by placing another "thing" above it with a thin insulator between.

Dan - Owner

http://www.Hi-TecDesigns.com