Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Need Help Identifying PCB Design Feature

Need Help Identifying PCB Design Feature

Need Help Identifying PCB Design Feature


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!

RE: Need Help Identifying PCB Design Feature

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.

RE: Need Help Identifying PCB Design Feature

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)?

Dan - Owner

RE: Need Help Identifying PCB Design Feature

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

RE: Need Help Identifying PCB Design Feature

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.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Need Help Identifying PCB Design Feature


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


RE: Need Help Identifying PCB Design Feature

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.

RE: Need Help Identifying PCB Design Feature

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).

Dan - Owner

RE: Need Help Identifying PCB Design Feature

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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close