Source: https://ozhealth.com.sg/product/genial-digital-thermometer-t15-orange/
I tore down a digital thermometer today (a Genial T15), and the interface to the LCD caught my eye: although there were conventional solder pads on the PCB, there was curiously no direct connection between the PCB and the LCD, which was offset some millimeters above by a rubber spacer of sorts. The entire assembly was fixed in a rigid enclosure (not shown) to prevent relative motion of the PCB and LCD:
My guess upon seeing this arrangement is that the LCD is capacitively coupled to the PCB, and the rubber spacer acts as a dielectric.
My questions are:
- Is this guess correct? Is there indeed capacitive coupling going on?
- What are the pros and cons of this design?
- Is this approach to interfacing with an LCD common in industry?
NOTE: I'm asking about a capacitively coupled LCD, not a capacitive touchscreen.
Best Answer
Rather than capacitive coupling, what you describe is probably an elastomeric connector. What looks like a rubber spacer is actually a piece of elastomer that is interspersed electrical connections that are arranged to carry signals through the connector in the vertical direction only.
The diagrams below show how the connectors are constructed.