Sniff is a "Scratch-like" programming language that's designed to help Scratchers move gently from Scratch to more conventional languages. They can start writing programs, without having to learn a new language because Sniff is based on Scratch. They learn a little more about variables, compiling, syntax errors (!), and they can have fun controlling real hardware while they're doing it.

Tuesday, 5 May 2015

Lego Wedo Alligator

The Lego Wedo is awesome! It comes with a great set lesson plans, with lots of great projects, and ideas for how you can use the items you build as part of larger topics. However they're firmly aimed at KS2, which is a great shame as everyone loves Logo and having bought expensive hardware, far too many schools use it for a few sessions in year 4, then put it back in the cupboard.

The Wedo software is nice but limited and expensive, and its probably the main reason that Lego haven't made the Wedo available outside of primary education. Fortunately the Wedo works with Scratch and Sniff. This means there's lots of opportunity for frameworking and progression: we can revisit familiar (and fun) projects which have been completed in the Wedo Software, and rebuild them in Scratch and subsequently Sniff.

My favourite official project from the Lego set is the Hungry Alligator. Building instructions are built into the Wedo software, but you can download regular instructions here: https://education.lego.com/en-us/lesi/support/product-support/wedo/wedo-base-set-9580/building-instructions

Now lets code this in Sniff:

make wedo device
make wedoConnector number
make wedoValue number

when start
.set wedoConnector to 1
.
.forever
..set wedoValue to -1
..tell wedo to "setMotorSpeed"
..
..wait 0.4 secs
..
..set wedoValue to 1
..tell wedo to "setMotorSpeed"
..
..wait 0.35 secs

We start by making a wedo hub device. You can connect any number of hubs (more or less!), but we're just going to have one. Each hub as two connectors, and we've plugged the motor into connector 1 (the left 1). We set the wedoConnector and wedoValue, and the tell the wedo to "setMotorSpeed". -1 closes the mouth, while +1 opens it (that's just the way this model is built/geared), so this code closes the mouth, then opens it, repeating forever. We close for slightly longer than we open to ensure that the jaws fully close - the drive bands will slip when we get that far.

Having got the jaws snapping, we can move that into a separate script.

when snap
.set wedoConnector to 1
.repeat 3
..set wedoValue to -1
..tell wedo to "setMotorSpeed"
..wait 0.4 secs
..set wedoValue to 1
..tell wedo to "setMotorSpeed"
..wait 0.35 secs
.set wedoValue to 0
.tell wedo to "setMotorSpeed"

when start
.forever
..set wedoConnector to 2
..tell wedo to "readDistance"
..repeat until wedoValue <0.07
...tell wedo to "readDistance"
..broadcast snap and wait
..wait 0.2 secs

Then we use the distance sensor to wait until there's something to eat! The sensor is on connector 2, and we readDistance until it reads less than 8cm, at which point we fire off the snap script. You may need to tweak the timings, and range value to get everything working smoothly (so the jaws don't trigger another Snap)


It's impossible not to love this guy! Just leave him sitting on your desk, and feed him occasionally! If you've got some Wedo kicking around from working with younger year groups, then get them out, and get excited about building and programming!

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