Help using the 18x Project Board

[jgillick]

I just bought the 18x Starter Pack which comes with the standard project board. I'm having trouble figuring out how to use it with the Pololu motor controller (http://www.pololu.com/catalog/product/411). What's really screwing with me is that it seems all the outputs go through the darlington driver which seems to output negative instead of positive on "high". Am I wrong?

Are there examples anywhere using this board?

Thanks,
Jeremy

 

[Dippy]

Can't help with motor controller but just a few words on ULN2803.

It is a low-sided switch basically and therefore switches your load to ground. Hence th appearance that it gos negative.

So, you connect +Ve >> LOAD >> ULN2803 - and switch it with a high from PICAXE.
I know it sounds a bit base-about-apex but there you are.

Here is a Data Sheet on the ULN280x.
http://www.farnell.com/datasheets/72791.pdf

Check page 2 to see how the NPN type transistors are arranged as Darlingtons and how they take the load power down to Ground.

Then just to confuse you even more they talk about Outputs when the current is going in!
It's just a convention . If they referred to it as an 'Input' then that would confuse it with genuine 'Inputs' (invariably to control an 'Output') - what fun!

So, think of it as a 'sink' Output. An 'output' because it is controlling external power. And 'sink' because the power is going in like water down your kitchen sink plughole down to the earth.

 

[cutlunch]

If you look at the interfacing circuits section from the Picaxe site it shows how motors can be connected to the ULN2803.

It can be found here:
http://www.rev-ed.co.uk/picaxe/