A Very Annoying Business Card

Solar powered business card designed to attract attention on a regular basis.

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A solar powered business card that emits attention seeking beeps every 2 hours to remind the recipient to send the ratcatcher an email.

The objective is to create a nice looking business card that's not too fat and that will remind whoever it was given to of the existence of the 'ratcatcher' every 2 hours or so with an annoying sequence of beeps.

Obviously, most of the cards will be given out with no electronics to those considered to be on the 'B' list ie mates in the pub. But if there's a serious looking 'A' lister like a billionaire living on a Caribbean island, then they get the version fully populated with electronics and battery.

The electronics is not completely ridiculous compared to the overall concept and features a small solar cell and energy harvesting chip to keep the lithium coin cell battery charged up. During the 'rest' period, the ESP32 MCU is completely turned off to save power and gets turned on through a transistor when the timer sends a pulse. A nifty CMOS logic circuit keeps the MCU in the 'on' state until all the annoying beeps have been broadcasted at which point everything is turned off again.. The energy harvester works at very low voltage levels and will charge the battery even when sitting on the billionaire's desk, assuming it is the right way up !

Another useful feature of this device is it's extreme low quiescent current due to the technical properties of the timer. It consumes energy in the order of 10 nano amps, which is less than the normal discharge rate of the battery.  If the timer is set to the maximum value of 2 hours, only a small amount of ambient light is needed to keep the battery charged. Setting the timer value is achieved by selecting the desired resister on the switch bank, with R = 174K giving about 2 hours.

The real question is: 'how long before the prospective billionaire either sends the ratcatcher an email (presumably to get his rat infestation sorted) or throw the whole thing into the Gulf of Mexico in disgust?'


sch - 84.50 kB - 06/16/2024 at 08:39



pcb - 117.00 kB - 06/16/2024 at 08:39



x-arduino - 1.11 kB - 06/14/2024 at 15:59


  • Device is now working as intended

    Dead Rat Productions06/21/2024 at 16:03 0 comments

    After removing the replacing the MCU, a short to pin 4 was cured and selecting the correct board in Arduino cured the pin definition problem. Turns out the MCU was fine, but the short must have been underneath it.

    Now it is sitting on a sunny shelve happily beeping every 2 hours and 17 minutes. Only problem now is that it does not seem annoying to me - I actually quite like it! I guess it would be annoying if somebody was trying to sleep though.

  • Card populated and MCU damaged during testing

    Dead Rat Productions06/17/2024 at 16:18 0 comments

    Finally got 'round to populating the business cards and fixing a few errors. I missed a few grounds on the logic gates, which was no big deal to fix, and found that the SEEED Xio SAMD21 MCU could not drive the buzzer directly and so had to switch in a ZTX 450  NPN transistor, which worked ok. Although the circuits 'kind of' worked, it seems that I have damaged the MCU, which is a bit annoying (pun intended)  probably trying to drive the buzzer, so that needs to be swapped out for a new one. Strangely, the buzzer still works although pin D1 now thinks it's D2, which is very strange. Pin 13 also works, powering the onboard LED, but none of the other pins seem to work. Hopefully easy to fix once the MCUs arrive from Digikey. Plenty of time before the competition finishes although fairly sure it's not going to win anything :(

  • PCBs arrived from PCBWay

    Dead Rat Productions06/04/2024 at 15:40 0 comments

    After a bit of friendly haggling over the number of business cards to be produced, Liam from PCBWay agreed to fully sponsor this project with some lovely gold ENIG plated pads, solder pasting stencil and perfectly reproduced artwork and email address font. I was worried about the font, but it seems most people have Verdana somewhere on their computer systems. It would be pretty bad if the address was in system font or some over strange offering.

    All of the circuits have already been tested so it should be just a case of placing the components and throwing into the reflow oven. A few changes to the design had to be made including getting rid of the ESP32 C3 board as it seemed to be a fake and replacing it with a fully branded and trusted Seeed Studio Xiao ESP32C3 Tiny MCU, which worked fine.

    One noticeable choice in the design is the battery holder. It's an expensive component, but in my mind very worthwhile. The worst thing I could do is fly all the way to the Bahamas to visit the prospective billionaire project investor with a business card that has a loose battery. With this battery holder, you literally have to prize the battery out with a screwdriver - it will never accidentally fall out or come loose!

  • Artwork and battery position alignment

    Dead Rat Productions05/11/2024 at 17:25 0 comments

    Basic initial layout looks ok. Main thing is that the battery fits inside the rat's abdomen. The timer module is just copy and pasted from another project so that should be fine. Just waiting to test a suitable IMU, which should arrive Monday-ish. Could be room for more than one buzzer, which could be fun.

  • Initial Concept

    Dead Rat Productions05/10/2024 at 12:52 0 comments

    The layout has to make sure that the battery does not interfere with the artwork. Fortunately, it fits nicely in the rat's stomach !!

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