a day ago •
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:
03/25/2021 at 03:04 •
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.
03/21/2021 at 23:06 •
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.
03/19/2021 at 04:03 •
03/14/2021 at 03:52 •
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.
03/08/2021 at 03:38 •
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:
02/28/2021 at 18:51 •
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:
---------- more ----------
- 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
* The tool had nothing to do with the quality of the schematic. I have no one to blame for that but myself. I am moving to KiCad because it is a much more capable tool and I have been burned by upverter updates in the past. I promise the new schematic will be a vast improvement.
02/27/2021 at 03:09 •
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.
02/27/2021 at 02:59 •
In this upgrade from my B3 Blinking Business card Badge, I upgraded the LED to RGB since I figured I would be able to change the color, but I forgot to check the harvested voltage, so the only one you can see when powered by NFC is the red LED. The 1.8V generated inside the LPC8N04 will not turn on the blue or green. In my next project I will add a capacitor and schottky diode so I can double the voltage by toggling an I/O.
02/26/2021 at 03:23 •
The LPC8N04 is only available in a QFN so hand assembly is not trivial. If you can live without sound, NFC EEPROM chips like the one I used in B3 are available in much more hobby friendly packages.
OSHPARK's flex service provides 3 copies of your design, so three strikes and you're out.
Swing 1, was a futile attempt with a soldering iron. The $15 USB soldering iron has been a reliable road warior, but it was no match for the fine pitch QFN.
I decided I needed to upgrade my gear for swing 2, so I picked up a station with hot air:
This was a nice improvement, but still not quite good enough.
I was starting to get discourage and I only had one attempt left so I had to make it count. The last flex sat on the shelf for several months until I saw a cute little board heater on twitter. It was under $100 so I decided it was worth a shot. I didn't quite realize how small it was until I open the package (feather for size), but it is large enough for most of my projects and just right for this job.
Third times the charm.