[simpits-tech] 16 channel output board is done!

[Gene Buckle]

On Sun, 8 Aug 2010, Sean Galbraith wrote:

> ...and I am assuming my name is already there... right Gene?
> Oh, and excellent work, as usual :)
>
Thanks Sean.  I'll post to the list when the boards show up.

Leo Bodnar brought a good point to my attention yesterday.  While the 
UL2803 can indeed handle 500mA per channel max, that's not what the 
devices as a whole can sustain.

I never thought to check, but the part has a max draw per channel of about 
150mA if you're driving all 8 at the same time.  The Toshiba datasheet for 
the part I'm using states a max dissipation of 1.47W.  At 5 volts, that's 
only 294mA.  At the voltage I want to drive it at (24vDC), it's less than 
100mA.

This is great for driving LEDs, but completely sucks for driving 
incandescent bulbs or more than one or two relays.  Just about every 
single digital output board that I've ever seen has _never_ mentioned this 
limitation.

When time permits, I'll look into crafting up a little daughter board that 
will hold 16 power transistors that can source up to an amp each.  What'll 
drive you guys crazy is in order to turn an output ON, you'll have to turn 
the corresponding Gaz16 channel OFF. :)  The good news is that I took this 
into account when I developed the firmware so it won't be too bad.  The 
board would need to drive all the outputs high on boot though - again, a 
simple tweak to the firmware.  Could even be made an EEPROM storable 
setting like the board ID is now.

How many of you downloaded the design and looked at the firmware source? 
It's the .PDE file in the archive - it's plain text.

g.



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