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Beeping, Blinking Business-card Badge (B4)

Second generation of the NFC business card adding audible feedback

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This environmentally friendly re-usable business card delivers a vcard with a tap and actively indicates the access with audio and visual cues. This makes use of the LPC8N04 ARM Cortex-M0+ with integrated NFC interface. Everything is powered from the energy harvested through NFC so there are no batteries to replace. The card provides a standard vcard NDEF that is recognized by most modern phones without requiring special apps. This is a great project for OSHPARK's Flex service.

This design was done in Upverter, so you can modify it in your browser without installing any software: 

Upverter B4-flex Project

Please note that this project uses an MCU that is only available in a fine pitch QFN which is not trivial to assemble.  The previous B3 Blinking Business card Badge uses NFC EEPROM which are available in larger packages that are more friendly for beginners.

I'll post the source code once I get a chance to clean it up a bit.

  • 1 × LPC8N04 ARM Cortex-M0+ with integrated NFC
  • 1 × PKMCS0909E4000-R1 Piezo Buzzer 9x9mm
  • 1 × B3U-1000P Switches and Relays / Switches
  • 1 × 155124M173200 RGB LED Side View
  • 1 × 0.1uF Capacitor

View all 6 components

  • Power Estimates

    greg07/30/2023 at 23:41 0 comments

    I assembled two of the test boards, one with ST25DV and the other with NT3H2211, then took some measurements with different loads.  

    Turns out the ST25DV does not regulate the output voltage, and it drops off with load fairly steeply.  The NT3H2211 is better regulated, and maintains the voltage better when loaded.

    The CH32V003 needs at least 2.7V to run and will consume between 2.3 and 1.9 mA depending on how many peripherals are enabled.

    The measurements are listed below and a plot of the output voltage vs load curve fit to the measurements.  This shows that the NT3H2211 provides a much more consistent voltage and stays above the minimum 2.7V up to a higher load current.  This suggests it will be easier to power the CH32V003 and a few peripherals with the NT3H2211, but there is not much margin.  

    I hear they are coming out with a low power CH32L103.  I wonder how the price of that will compare to the CH32V003.  It is available in the same TSSOP20 pin package, but it has more memory and advanced features like USB, which is not a requirement in this case.

    LoadST25DVNT3H2211
    No Load4.013.09
    1000 Ohm2.722.82
    500 Ohm2.372.66

  • Course Correction

    greg07/30/2023 at 03:41 0 comments

    It has been a while since I posted on this project.  I had some inspiration at CrowdvSupply Teardown 2023 and have been putting in some more time on this.  I’ve got a few issues with the NXP micro.  It only generates 1.8V from NFC which is only enough to drive a red LED without a voltage doubler.  It is also missing support from their SDK on GitHub.  

    With the WCH CH32V003 available for about a dime in volume, I could use it with a I2C NFC EEPROM for about the same price, and drive an RGB LED without a voltage doubler.  The CH32V003 is not specifically a low power device, so I decided to see if it would be feasible to drive this from the NFC harvested power.  It only runs down to 2.7V, so I need to know if the NFC chips can deliver that when loaded.  There are a few options available with energy harvesting output.  I’ve used the ST25DV in the past, and NXP has a couple similar devices like the NT3H2211, or NTP53321.  The data sheets are pretty sketchy on how much power is available, so I decide to measure it for myself.  

    I designed a board to test a couple of the device.  The ST25DV and NT3H2211 are both designed with 50pF load capacitance, but the NTP53321 is designed for a different load cap, so it would require a different tuned antenna.  I already have an antenna I’ve used for 50pF load, so I designed a board to test the two 50pF chips.  Unfortunately they have different pin outs, so I had to put down two footprints in parallel.  I added the CH32V003 and a current sense amp so I could see how much current it is using.  I used my badge as a template and shrank it to save a little on the OSHPark price.  I kept the bannana plug/alligator clip pads for measuring voltage and current.  I’ll share more about what I found in another post.

  • More details on B5

    greg04/20/2021 at 01:19 0 comments

    My progress been delayed by samples getting stuck in customs.  I would have preferred to have tested out the design before sharing more, but I can at least provide some of the theory of the design that I ordered from OSH Park.  It looks really good in after dark.

    Here is the schematic for the design:

    As I mentioned in the last post, I included two buzzers as a stuffing option.  You can see how they overlap in the picture of the board.

    Another interesting thing to note are the three resistors, R5-7.  These are another stuffing option I will be testing.  As shown they are three different load resistors that I could use for impedance measurements.  I am hoping that the loading of the current to digital circuit will be sufficient for my measurements so that these are not needed.  If they are not needed as loads, I may use them as reference values for calibrating the impedance measurements.  I expect reference impedances will be more useful than the programmable loads.

    The current to digital circuit measures current integrated over time which is perfect for counting coulombs into a capacitor.  The voltage rise per coulomb is proportional to the capacitance. 

  • A Dilemma, A Hedge & A Hack

    greg03/25/2021 at 03:04 0 comments

    To improve performance while operating from harvested power, the LPC8N04/NHS3152 suggest adding decoupling capacitors to a couple of the high drive GPIO pins.  There are four high drive GPIO pins that also happen to be the timer/PWM pins.  This allows us to use two for decoupling and two for the piezo buzzer.  The dilemma is that the SWD signals are also on two of these high drive GPIO, so I have to choose:  do I want to give up decoupling or buzzer when I am programming/debugging? 

    I can provide power externally when programming/debugging, so I could easily give up the decoupling, but SWD may not work with the capacitors installed, so I may need to add and remove them often.  On the other hand, I only need to remove a single resistor to eliminate the load of the piezo buzzer, and if I use a large enough series resistor, SWD may even work with the resistor present.  But, if I share the buzzer with SWD, I can't use them at the same time.  To hedge my bets, I will put decoupling caps and a buzzer on both pairs so I can extend my indecision until I assemble the boards.

    The buzzer is one of the largest parts on the board, so adding a second one adds bloat, but there is really no point installing them at the same time so they can share some space.  I placed them so they overlap on the board.  You might think the hack is ignoring all the placement errors in KiCad, but the real hack is that the silkscreen for the buzzers goes right over the pads for the other buzzer.  I know that OSH Park clears silkscreen off pads so I left it there.  I can clean it up in the next pass when I figure out which stuffing option to keep.

  • Zero height connector

    greg03/21/2021 at 23:06 0 comments

    A business card or badge should be as close to flat as is possible.  With the new features I am adding I want to provide convenient connections without adding to the thickness of the assembled board.  A 4mm plated through hole with an oversized pad is ideal for this application.  It is probably the most utilitarian connector you can put on a PCB.  It adds zero height and zero cost, and it works with banana plugs, alligator clip, and screws.  Banana plugs are the perfect connection for a multi-meter.

  • 'B' is for Banana Plug

    greg03/19/2021 at 04:03 0 comments

  • Displaying data without an app

    greg03/14/2021 at 03:52 0 comments

    In my latest spin, I traded the LPC8N04 for the NHS3152 so I can make use of the added analog features.  The added ADC will allow for reading voltages, so this business card will be able to act as a volt meter. 

    The NFC Forum defines NFC Data Exchange Format so NFC devices know how to communicate with each other.  Using one of the standard formats allows phones to recognize the data and act accordingly.  The business card uses a standard v-card type to share contact information, but there is no standard type for a volt meter.  I could create an app to implement a custom NFC protocol, but there are some other standard formats that can be utilized without requiring a custom app.

    One very flexible format is the URL type.  This format exists so that you can tap a tag that will direct you to a website.  To enable reading the voltage without an app, I will create a voltage display web page and pass the data to the page in the query string of the URL. 

    This way the business card/badge will also serve as a volt meter that doesn't need batteries and never needs to be recharged.

  • I think I found another "B"

    greg03/08/2021 at 03:38 0 comments

    I have been working on an update to light up the blue and green LED's and to add some additional features.  Just placed the order with OSH Park.  I'm excited to try their after dark service.  Here is a sneak peak:

  • To Do List

    greg02/28/2021 at 18:51 0 comments

    The current design is a functional Beeping and Blinking Business card Badge, but there are a few improvements I would like to make.  Here is some of what I hope to accomplish in a future update:

    • Re-enter design in KiCad and try to move past the shame of the disgusting schematic I created in upverter.*
    • Add voltage doubler to light green and blue LEDs from harvested power
    • Add cap to an I/O pin to store harvested energy
    • Migrate to NHS3152 to get analog for new features
    Read more »

  • Lessons Learned - NFC

    greg02/27/2021 at 03:09 0 comments

    To be useful as a business card, I can't expect a stranger to load an app to get the vcard.  This means I need to use the standard vcard NDEF and live with the power that provides.  That only lets me play a couple quick tones.  I was hoping to find a way to trick the phone into reading longer, but I haven't found it yet.

View all 14 project logs

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brucejdii wrote 02/26/2021 at 23:52 point

A Flexible PCB AND a NFC device - an AMAZING Double Whammy!   I'm glad that you posted the "first attempts".... it gives understanding and hope to those who undergo such ordeals- that it takes practice to develop the skillz...

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