Heart Spark

The Heart Spark is a heart-shaped pendant which flashes little lights (light emitting diodes, LEDs) in time with your heart beat. A polar chest strap with transmitter (sold separately, see more information below) is used to measure your heart beat, which is transmitted wirelessly to the pendant. An arduino-compatible circuit captures each beat as it happens and flashes LEDs. The pendant is carefully designed to maximize its visual appeal, including symmetry and a high-gloss epoxy coating (as pictured to the right). A CR2032 coin-cell battery provides 8+ hours of battery life. Two small switches on the back allow selection of operating mode:

back1) Both switches down: Fake Mode. The pendant will flash all six LEDs at a steady 75 beats per minute (BPM) regardless of the presence or absence of a polar transmitter. This allows the pendant to be used even if you do not own a polar chest strap. Or more nefariously, you can look calm when you are not 🙂

2) Left switch high, right switch low: regular blink. All six LEDs will flash in time your heart beat, as sensed by a polar transmitter / chest strap. Faster blinking means your heart is beating faster; even without practice it’s easy to tell the difference between resting/calm heart rate (70 BPM) and elevated heart rate (100 BPM).

switch3) Left switch low, right switch high: activity blink. The number of LEDs that blink corresponds to your heart rate, as measured by the polar transmitter:
<80 BPM: 2 LEDs 80-90 BPM: 3 LEDs 90-100 BPM: 4 LEDs 100-110 BPM: 5 LEDs >=120 BPM: 6 LEDs

This mode allows you to know at a glance the numerical value of your heart-rate in a small range covering ordinary activity. It also has the benefit of saving power in the low-activity range.

4) Both switches high: circle blink. The LEDs blink in a circle each time the polar transmitter detects a beat.

Video of the three real-heart-beat operating modes:

The pendant has two holes, into which jump-rings are placed. The pendant can come with a variety of necklace options (see photos below):

A) nothing – supply your own
B) Metal hoop: choker-style metal hoop around your neck
C) Nylon rope with metal crimped ends
D) Metal chain with magnetic clasps

Note that if you use choose the metal chain you need to be careful during battery insertion that the metal chain does not come into contact with the battery holder, because you might short the battery to ground. Once you are wearing it, the chain is naturally held away from the battery holder, so it’s really only when you are not wearing it that you have to worry.

Each Heart Spark ships with 4 CR2032 coin cells. More batteries can be purchased online, or at most drugs stores. CR2032 is the most common form of coin cell. Battery life is 8-12 hours depending on mode.

To make the pendant blink in time with your heart, you will need to own or purchase a Polar transmitter and chest strap. Sensebridge recommends the Polar Wearlink Transmitter with Chest Strap, which you can get at REI, or MEC or Amazon.com or hundreds of other locations worldwide. We’re also fans of the NuMetrex Apparel which is designed for use with polar transmitters, and is slightly more comfortable than the default chest strap. If you do not own or purchase a transmitter, the Heart Spark will still blink, but only at a steady 75 BPM with no relationship to your real heart beat.

The Heart Spark comes with epoxy coating. See the picture to the right: the shiny one has the epoxy, we think it makes a huge difference in how awesome the Heart Spark looks. If you plan to program the device you’ll need to remove the epoxy to access the programming headers, because the epoxy makes the programming pinouts nigh on impossible to access. You can remove it by heating it up a little with a hot air gun (not a lot, it tends to make nasty smell when hot) and poking & prying at it with e.g. a dental pick, or a pair of fine tweezers. In my experience it comes off remarkably easily.

The Heart Spark V1.0 is $69 plus shipping & handling ($5 to Canada, $10 to USA and rest of the world). It will ship from Canada via the regular postal system, carefully packaged in a bubble envelope. Canada listing is in Can$, USA and rest of world pay US$.

Necklace Style

See also: the Sensebridge.com page on Heart Spark, it’s got photos of the new black Heart Spark, which is likely what you will actually receive since the green ones are now almost all gone.

Thanks to Elizabeth for modeling the Heart Spark:

Metal Choker
Metal Choker


Chain with Magnetic Clasps
Chain with Clasps