My current business card (ok, actually a personal card; my day job business cards are not nearly as awesome) is a 3 channel wireless solenoid controller:

If you’re able to read my phone number, please don’t call me in the middle of the night and breathe heavily into the phone.

Here’s a picture of the assembled card. Pay no attention to the mangled legs of the power regulator; this is a picture of the first prototype, and has since been fixed.

Also see the better copper fill around the Site 3 Fire Arts logo in the first PCB picture.


I do give these cards out to people during normal business card exchange rituals. So, I chose to use only through hole parts: people often have little or no experience assembling electronics, so it was designed to be as easy as possible. XBee radios were also chosen for their ease of use.

The card itself is the same size as a normal business card. I have them made on 0.8mm FR4.


The card has two separate power inputs: one for the control system, and one for the solenoid power that it switches. This allows the card to be powered off a 3.7V LiPo battery (with 2 pin JST header) or 3xAA/AAA battery pack, while switching 12V, 24V, or higher voltage DC to activate the solenoids.

Since this was designed for fire art, having a separate solenoid power source allows a deadman switch inline, so the dangerous side can be shut down immediately while keeping the controller side active. The two sides are separated via optoisolators.


The card uses an XBee radio (Series 1 or 2) for wireless communication. The card does not have a microcontroller on it: the outputs are triggered directly via DIO lines 0 – 2 of the XBee.

This means that a Series 1 radio is preferable, as they can do IO line pairing: change the IO line on the sending radio and it will trigger the output on the receiving radio automatically. Series 2 radios will also work using a remote AT packet to control the line.

Solenoid control

The solenoid power is switched using MOSFETs. Each channel has a LED indicator that lights up only when the channel is active.


Bill of Materials

Found in the wild

I use my card as a way of controlling fire out the eyes of a giant metal cat skull cutout:

This is what happens when the solenoids are activated:

Here’s the controller I built. Since I only had Series 2 radios around, the remote has an Arduino Pro Mini in it which reads the button press and sends out a remote AT packet to turn DIO0 on and off. Also, I specialize in making sketchy-looking detonator things.

I haven’t yet seen someone using one of my cards for their own project. If you have, send me a picture and I’ll post it here.