Hi, I’m Mark Longstaff-Tyrrell. I’m an electronics engineer and I’m at Fab Lab today
to talk to you about the STM32L476 Discovery board.
This board is produced by ST to showcase their range of low-power microprocessors.
The device is a 32 bit arm cortex m4 core with a floating point unit like the rest of the Discovery boards range
it comes with a built in USB programmer so you plug in directly into your PC and start developing with a range of software tools available.
The key feature of this device is it's incredibly low powered consumption.
It can be powered from a 3 volt coin cell and the board comes with some firm ware to demonstrate those very low power modes
which makes this device great for developing for, battery powered applications such as wearable devices.
It comes with a built in LCD screen and also a USB on the go port, which can be configured to support a range of devices.
On the back of the board, there's two rows of headers which can be used to access some of the spare IO lines
from the microprocessor and interface them into your own projects.
So to demonstrate some of the capabilities of this board and this device,
I've developed a radar speed detection system.
This uses an off the shelf radar motion detector, so I'm gonna use the on board,
analog to digital converters to sample the output of the radar, then use the floating point unit and the DSP function to calculate the spectrum of that signal
and then look for peaks in that spectrum, which correspond to the radar returns from the larger objects in the senses field of view.
By calculating the frequency of those returns, I can calculate the velocity of those objects and display them on the built in LCD screen
I can also use the USB port configured as a serial device to dump the sample data as well as the spectrum that's been calculated to a PC so we can look at that spectrum, use that for debugging.
I've also configured the audio deck, to output the samples of data so we can listen to that signal as well.
So I've set the board up to show the functions that we're going to use to implement this doppler speed radar,
at the moment I've got the board connected to a signal generator which is going to simulate the output of the doppler radar, when there's an object approaching.
On the PC screen you can see the radar output at the top in green,
and at the bottom you can see the calculated spectrum that the microprocessor on the board is calculating.
And that frequency output is going to be proportional, to the velocity of the object we're measuring.
So it's a fairly simple calculation, so you convert that into miles per hour or meters per second
and that's done by the device and displayed on the screen.
So, now let's plug the radar in, and we can see the real output.
So this is the radar module, that I've developed. It's got the doppler radar module here
a simple, off amp amplifier which gives a gain of a few thousand, to amplify the micro volt range output from the radar
into some signals we can detect with the board.
This additional board is to supply some power supply filtering to clean up the digital power supply from the ST board.
I've used the same connectors that work with the ST board so it will simply plug in
and now we can listen to the output of the radar through the speakers.
So for slow moving objects, you can hear, it's quite a low frequency.
So in order to simulate an object moving on the bench top, it's much more convenient to use a small fan like this
which can provide the illusion of a moving object to the radar and you can immediately hear the doppler return of that fan running.
You can see it on the screen.
So now we're outside FabLab and we're going to try and test the device by measuring a cyclist going past.