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This PCB is from a HomeLink garage door opener module for cars. Specifically, the Gentex 960-0218. I'm trying to understand these pins and the design:

PCB

They were originally wired to a vehicle this way:

  • Pin 1: connected to gray wire
  • Pin 2: connected to black wire
  • Pin 3: dummy (not connected)
  • Pin 4: connected to tan wire
  • Pin 5: connected to red wire

This board has three LEDs that light up when the headlights are on (they are the yellow squares), and three black buttons to configure up to 3 different garage doors. The orange board, based on FCC filings, is a separate board that is a 288-433 MHz transceiver that communicates with the garage door

Based on posts on the Internet about similar modules, these pins are:

  • Pin 1: "Variable +12VDC" or "variable ground" (for button illumination)
  • Pin 2: Ground
  • Pin 3: not used
  • Pin 4: +12VDC for button illumination
  • Pin 5: +12VDC

I tried following the traces and I couldn't get very far. Pin 1 is connected to an SMD labeled "DT" and a 222Ω resistor, and pins 4 and 5 are connected to these pads right next to them. I can't see the other side of the board.

Questions

  • Does the pinout above even make sense, given the information I have?
  • I probed the buttons (see picture) and I think those are all ground and have continuity between them, but it ends when I follow the trace to the via circled in red. There is no continuity between those pins and any of the pins labeled 1-5. Shouldn't the ground for these buttons be connected to the ground pin?
    • Does this mean there is a broken trace?
  • What is "variable ground"? Couldn't the LEDs share the same ground as the rest of the board?
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    \$\begingroup\$ There's no attribution to the picture and same question was asked in Reddit a few hours ago. Asking the same thing in multiple separate places wastes effort as different people work on same question on different sites without updates between sites. \$\endgroup\$ Commented yesterday
  • \$\begingroup\$ @Justme I apologize, I didn't realize this was not allowed. I've deleted the reddit post. I took the picture myself, not sure what you mean by attribution \$\endgroup\$ Commented 5 hours ago
  • \$\begingroup\$ Giving proper atrribution simply means stating where the picture came from, whether you took it yourself or took a screenshot of a book, but it must be statet what book it is or from which website you pasted a photo here. \$\endgroup\$ Commented 23 mins ago

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  1. The pinout may make sense if that's what you read from the Internet. To know the pinout for sure you need to reverse-engineer how it works and needs to be connected. Or find a manual.

  2. There is no need for the buttons to have ground on one end. It might not be ground. You verified it's not connected to assumed ground. So it could be anything. There is no way of seeing how those buttons are read, and assuming one end of the buttons is ground may be a wrong assumption. To be sure, power up the module, measure voltages with multimeter, look at waveforms with oscilloscope. It might be the positive supply of the module instead of ground of the module.

  3. We cannot know what the term "variable ground" or "variable 12V" on that pin means for this module, if it is used for illumination. Maybe it is a translation error. Maybe it is used for dimming the lights like for other illuminated buttons.

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  • \$\begingroup\$ On the second point, is ground not strictly required then? There is no continuity between any of the pins labeled 1-5 (which are the only ones actually connected to the car), and any of the pins on the black buttons. I'm sorry if this is a dumb question, my experience with electronics is limited to simple Arduino/Pi type of stuff, where I'd wire the ground pins on buttons like those to the ground rail on the breadboard. \$\endgroup\$ Commented 9 hours ago
  • \$\begingroup\$ Oh, I just found out all those pins are wired to a diode. This pretty much confirms it's not ground, right? \$\endgroup\$ Commented 4 hours ago
  • \$\begingroup\$ @Confluence Nothing prevents you from wiring buttons to MCU supply, so that button pushed gives logic high and button not gives logic low (does need a pulldown resistor which may not exist internally in alll MCUs).And who knows what the diode is for. The 0V of the MCU does not need to be the 0V of the car, what if there is an isolated supply regulator for powering the components? \$\endgroup\$ Commented 52 mins ago

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