Puck.js Capacitive Sensing - NFC Ring used for Puck.capSense()?

[espruino-discuss]

Posted at 2017-04-27 by intern

Hi all,

I would like to get some clarification on the capacitive sensing capabilities of the Puck. The documentation of the Puck.capSense() mentions this:

TX must be connected to RX pin and sense plate via 1MOhm resistor.

I've read through the circuit diagram, and I thought the TX is already connected to the RX and sense plate via a 1MOhm resistor, is this referring to another external 1MOhm resistor?

If no pins are supplied, the NFC ring is used for capacitive sense.

What does "no pins are supplied" mean?
Does this mean since the Puck has pins D11 (exposed) and D12 for capacitive sensing --> pins are supplied --> so it does not use the NFC ring?
Or does it mean when nothing is connected to D11, the NFC ring will be used for capSense instead?
But when I go through the circuit diagram there doesn't seem to be a connection from the CAPSENSE_TX and CAPSENSE_RX to the NFC wires, so how does capSense uses the the NFC ring on the Puck?

Thanks.

[gfwilliams]

Posted at 2017-04-27 by @gfwilliams

Hi, I'll update the docs for this - it's pretty misleading.

• Just calling Puck.capSense() on its own will use D11
• If you call Puck.capSense(tx,rx) with your own pins, you need a 1M resistor between the tx and rx pins, and to connect the thing you're checking to the rx pin.

Originally Puck.js was going to use the NFC ring for capacitive sensing, but when I started trying it with devices in a case, it was almost unusable (it couldn't reliably detect a hand over it) so I had to switch to just having a pin set up for it (D11) - it looks like I forgot to change the documentation for the function.