Let's Make Robots!

Working on a PICAXE board for robot building - working on v0.9

I'm getting on with making a small PICAXE-driven board similar to the uBotino. I've got it moving along and am ready for other thoughts at this point.

A quick copy/paste from my blog with a little more info:

The Rev-Ed board is nice but there are a few features I don't care for. My PICAXE 20X2 Robot Builder Board does away with/adds those things. And it's only 50mm square.

2nd ed.-

  

post Ro-bot-X mods:

Post CtC and ignoblegnome suggestions (click for full size):

   

v0.6.2 (added switched power to SN754410 per ignoblegnome's observation):

 

version 0.8:

 

The list of features I'm aiming for:

  • Powerful X2 series processor (Rev-Ed's board uses M2/X/M processors)
  • Can use 3AA alkaline, 4AA NiMH, or higher voltage battery packs with the 5V 3A LDO on-board voltage regulator (can be disabled for AA battery packs)
  • Included quad H-bridge driver for bi-directional control of two small motors with power supply selection
  • Option for PWM of motor driver's ENABLE lines for speed control
  • Five pins available for working with servos or LEDs (resistors selected with individual DIP switches)
  • Selectable power source for Port B power header via jumper (allows use of 6V or 7.2V for servos, in particular)
  • Ability to use both SEROUT and A.0 pin on leg 19, jumper selectable
  • Robust screw-down terminal blocks for power connection
  • Power indicator LED

There isn't much wiggle room for adding features but I am eager to hear public opinions, wish lists, wut-i-wudda-duns, etc.

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With v0.6 you reintroduced 90 degree traces. 

What is the diameter of those mounting holes? The actual hole is the little circle not the big one in case some do not under stand. I make my hole 2.8mm for little #2 bolts. 

Yes, I'm now working on clipping the 90degs on the traces. Good eyes :)

The drill holes are 3.2mm which is actually the big circle as you described it. I might opt for those #2 bolts. It seems everyone uses #4-40. That's the only reason I chose that size.

I also use the 3.2mm holes, because in some countries, people use metric bolts, like M3 which needs at least 3mm hole. M2.5 are hard to find, but still you can find them in some places. Besides #4-40 bolts I did not find tinier bolts easy, like in a hardware store or Home Depot. Home Depot does not have smaller bolts and only some hardware stores have smaller bolts. Also, the spacers available at robotics stores are either #4-40 or M3.

Also, I looked at the traces for motors, they are a bit too wide to pass between 2 IC pins. Make sure you do not cross the outside circle for any pad, that is the minimum safe distance. Oh, and I also use a bottom ground plane and a top Vcc (5V) plane, kind of works like a capacitor, you get less electrical noise.

A #4 fits in the 2.8mm as well.

The board looks great, but the mounting holes seem a bit tight. There might not be enough room for a screw or a nut there.
And are the DIP switch all that useful?

Working on adding room to the mounting holes right now. It is very tight indeed. It might become only three useful holes and a vestigial fourth hole. Eh.

The switches are to add 330ohm resistors to the I/O lines. PICAXEs need them for servo signals and for LED work. I put them on switches to keep the pins multifunctional and to avoid an endless sea of male headers on the board. If you have another idea on how to do it I'd be keen to hear it, Mr. Andersen.

I second on that 3A, 4-Pin volt reg. Gosh-darn-good regulator.

Thanks, ig. I had a spare 3-pin sitting on my schematic for the longest time and I just deleted it. I knew I pulled it out for something.

Clipped my 90deg trace angles too, per CtC's advice. Quiet circuits are happy circuits.

Added caps per Ro-bot-X's recommendations. Unable to accomodate any 10uF's to go with the 0.1uF's. Got the power LED in there too.

One minor design change: moved the SN754410 to different pins to allow use of the PWM function. I thought that might be nice.

Hey, you're using my favorite LDO voltage regulator. Good on you!

bOd

 

It looks to me like the power to the motor is unswitched. Is this on purpose?

 I still don't get your power routing to the motor supply. Seems unswitched. I guess it isn't a problem since the motor driver chip logic won't be powered?  But it doesn't see like it'd be hard to run switched power instead.