Monday, October 26, 2009


Hello again,

Well, we've finally got a proof of concept. We decided to do a two-machine proof of concept - in which both machines are in directional antennae pointed the same way. One machine pings the other, and in order for the ping to be received, it must bounce off of something in front of the setup for the other computer to receive it. When the other computer receives this ping, it sends a response back to the sender which also must bounce off of the object in front of the rig. When the sender receives the response, it calculates a dT which we can use to approximate how far away the object is from the rig.

We're using bootable SLAX thumb drives with BlueZ loaded into them. We're using the l2ping command to ping over bluetooth. We have both machines in cardboard boxes lined with tin-foil to make a directional antenna.

Results are promising, as we can already see differences in the raw ping times. With some signal processing, we could probably even see more detail in our times. We're currently just flood pinging the other laptop and qualitatively examining the times we get.

This isn't a true dopplar radar, but the more we research what's available to us, we probably won't be able to get a dopplar shift from consumer grade hardware. We'll likely have to build our own hardware using an antenna/ADC. This proof of concept is good enough to show considerable distance differences (1, to 9 meters with reasonable resolution). We will be unlikely to get MCG information from this rig.

Source code has been posted to google code. It is currently just a renamed version of l2ping, but as we add our own signal processing to the response times the code will slowly morph into something more directed toward dopplar radar.

In other promising news, we found that BlueZ allows us to ping a secondary bluetooth device connected to the same laptop. This brings the machine count down to one - a necessity for our second milestone. Huzzah!

And in other news, BlueZ is apparently used in Android. Mobile dopplar ahoy!


Tuesday, October 6, 2009


We're currently performing research into the MCG Project, and we've finally hit pay-dirt. We figure we can perform an MCG using data packets rather than raw analog signal. Here's how we're thinking about doing it:

We send a data packet with a pseudo-random number encoded in it. We open a window shortly after this message is sent - initially a very small time interval after - and listen for the echo, checking that its the same PRN. If it's received in this time window, we know we have a signal. We can vary the window from very short to longer time intervals in order to get a broad spectrum of dopplar times. From this - we can perform some signal processing to determine where the heart beat is.

It's a very high level idea at this point, and much needs working out. The importance of this idea is more relevant to the hardware side of things - it's finally feasable to use consumer level electronics! We just need to look into enabling full-duplex communication on the same frequency with bluetooth/802.

More to come.