October 28, 2008 – 9:32 pm
Yep, more shopping. I found the Technobots site recently whilst searching for screws to support the pan/tilt unit, as the velcro tape isn’t coping too well. Whilst there I somehow ended up in the lighting section and so some Dimension Engineering Ultra Bright LEDs made their way into the basket, despite my not being at all sure I’d be able to use them with the Qwerk!
As advertised, these LEDs do come with a servo-style connection, but there are only two power pins, with control absent; presumably the DELight controller just varies the voltage directly to adjust brightness. Hooked up the qwerk’s servo ports, the LEDs work- and they’re not joking about the ultra brightness - but are purely decorative, since you can’t even switch them off.
So, armed with my wire strippers and extremely limited grasp of electronics, I set about trying to hook them up to the Qwerk’s analogue outputs. Then realised it doesn’t have any, and that what I was looking at - the screwdown terminals on the same side as those for the motors - were digital outputs. Still, that at least lets me turn them on and off, so I separated the wires (easier to do this with the servo clip still in place), cut off the clips (no going back now) and stripped some of the insulation. Then it was just a question of which wires to connect where…
There are ground (GND) and power (5V) terminals, as well as numbered terminals 00-03 and 10-13. The Qwerk hardware guide reckons these latter are input and output pins respectively, but this is actually backwards! I shunned the 5V on the assumption that this’d drive the LEDs permanently, and connected the red wires from the LEDs to 00 and 01 (second time around), with the brown wires going to ground pins. It should be noted that this is the movie bomb disposal approach to electronics - crossing fingers and choosing a random wire - but fortunately it worked just fine, and a quick test with the universal remote proved I could switch the LEDs on or off.
What’s the use? The Qwerk does have 10 built-in LEDs, but these already indicate useful data such as connection mode and activity. So (besides the challenge of attaching new stuff) I wanted a way to indicate the status of running code of my own; often it’s hard to monitor both the robot’s behaviour and text output on the host computer. For instance, I’m planning to modify the object tracking code to use green light when it has a lock, and red when the object has been lost. For autonomous roaming, I could use the LEDs to indicate whether the robot thinks the left or right direction is safer, for an at-a-glance check as to whether it’s processing sensor input correctly. Plus, well, science fiction films have taught us that all robots need the ability to glow red when angry, and all the on-board LEDs are green, so I had to correct that
Higher resolution pictures of the assembly process and end result can be found in the gallery.
Expense-ometer: £513.75 so far.
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