Tag: DIY

MSP430 Launchpad: LED as PhotoDiode

Posted by on February 28, 2011


I’ve been meaning to build a “line seeker” robot for a while now, however I can’t source LDRs (Light Dependent Resistor) due to RoHS nonsense, so I decided to use plain old LEDs instead. While you could use a couple analog amplifiers and comparators to do this I thought it would be a fun little microcontroller project.

Right now we’re just exploring how to utilize a regular LED as a photo-diode, ie. an input sensor.

There are a couple ways to accomplish this – I chose the simplest for the time being – The idea is to sample the voltage present on the LED anode (or cathode!) by using the ADC on the MSP430, this voltage will be relative to the ambient light. You could picture the LED as a solar cell in this case.

The code:

We’re going to use the on-board LEDs on the LaunchPad to simplify things. The Red LED will be our “sense” input and the Green LED will be used to depict the current state of the sensor.

You’ll have to modify the header (and your project target) depending on which MCU you’re using, I happen to have a G2452 currently populated for another project I’m working on, but you can use any value-line MCU as long as it’s got an ADC.

Why so vague?

Lately I’ve been suffering a serious mental block, I would really like to explain the theory behind all this but not only am I uninspired I also can’t focus on writing… I would however recommend you Google “LED Sensor” (or similar query) to learn more about the subject.

Have fun.

MSP430 Launchpad: Random Software Delays

Posted by on December 13, 2010

The goal: to “randomly” flash the on-board LEDs at P1.0 and P1.6

The weapons: CCS, Launchpad, Cookies (you may choose your favourite ones)

The reason: To familiarize yourself with the coding environment, or just for the heck of it.

The library:

That’s our random library, it’s grand.h

The “g” prefix is one I often use privately, it’s simply the first letter of my name. However because there may be other routines in the future with a similar naming convention, having “g” prefixed is not a bad idea; without having to fall into namespace gibberish.

The PRNG is an old standard. No need to discuss it.

You may recognize those macros, yes! They’re from Quake3! — Although we aren’t using them I left them there for future reference on how to obtain usable value ranges from the PRNG. There’s a lot to be said about floating point values and whatnot, But I’m going to restrain myself in this case.

Now to the main code:

No external hardware is required, just make sure both P1.0 and P1.6 jumpers are set.

As you can see we’re simply toggling the LEDs with a random delay, the delay_ms(); function was taken from here.

Like I said there are quite a few topics to explain, however I decided to keep this one as simple as possible (Alright, I’m in a rush!)

So… Compile, run and enjoy!

Once I get the time I’ll put together some utilitarian code libraries and lengthier explanations, promise.

For those interested, you may download the entire project directory from here: Random Software Delays.