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  • Author Author: Fred27
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Combined NFC reader / keypad

Fred27

So, the board is back from the fab. It looks really nice - especially as it only cost $1 (+$8 shipping) for 3 from Seeed. It's been pasted, populated and toasted and ready for test. Well - it would be ready for test if it wasn't missing just one component - an out-of-stock 32.768kHz crystal.

image

The board will eventually be the way into my house. There's a small NFC antenna that I'm hoping will be tuned well enough for the tiny NFC implant in my hand. There's a capacitive touch keypad (hence the MSP430FR2633 microcontroller) because even I don't think getting my kids chipped is a great idea.

 

Unfortunately without the missing crystal it will be a pain to get the capacitive touch or the SPI comms with the TRF7970A NFC transceiver working. I'll wait for it and work on other stuff for now.

 

I can confirm that the reverse mount RGB LED that shines through the circular gap in the soldermask seems to work really well though. The FR4 diffuses it nicely. Blinky is always a good start to prove the MSP430 is running happily. I'll have to wait to see how my QFN soldering went. It looks borderline under the microscope. This time I decided to solder down the thermal pad first and check alignment and then use some paste and a hot air gun to do the leads. That should minimise the chance of any shorts under there that I can't see. At least I hope it does - I've never tried it that way before.

  • in reply to Fred27

    I can see where that might be problematic.  With capacitive contact there should be coupling (albeit less) with partial contact with a smaller finger.

     

    Gene

  • in reply to genebren

    I'll certainly try tuning. The problem may be the design of the mutual capacitive button that's based on a TI design. They consist of two rings - one about 10mm diameter and one about 7mm. An adult finger covers both altering the capacitance. My son's finger completely fits inside the inner one.

  • in reply to Fred27

    David,

     

    Having worked on a few different capacitive touch sensors, I do believe that tuning should be able to help.  Not sure if your functionalities are coming from within a library, but I believe that the trips levels should be tunable.  I wonder too, if by lowering the thresholds, if the touch be a larger finger might possibly force adjacent contacts into a false touch.  Again, thinking out loud, but if there is some confusion in adjacent contacts, if you might be able to use a calibration step to set the thresholds, i.e. press and hold the touch on '*' or '#' to determine the thresholds, then setup the pad for the code input.

     

    Still,very cool!

    Gene

  • in reply to Fred27

    It's looks really nice with that black soldermask. I think v2 should have a beep after every key is pressed image

     

    Luis

  • The capacitive touch keypad is also working pretty well, including decoding key presses and checking for the right code. The proximity / guard sensor works, but may need some tuning so I've disabled it for now.

    Unfortunately, the 10mm mutual capacitive sensor buttons work just fine for me but seem to have a bit of trouble detecting my 4-year-old's tiny little fingers and it is really meant for him to use. Not sure if tuning will sort this out or if a redesign of the key is in order.