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.
Hi Jax, I have a few observations about your design. At this moment there are no traces, but I’m sure you’ll run into problems if you keep this layout, especially trying to route the traces for the motor connectors (I believe they are Lt and Rt?) I suggest to move these connectors to the side of the H-bridge. Also, it might be better to move the motor power selector to the bottom of the board, so you have more room to route the traces for the second motor connector, first one being directly in front of the motor output pins on the left side of the board (a bit closer to the mounting hole, to make room for the other connector). Moving the motor connectors to the side of the board will allow you to move the 3 pin connectors between the H-bridge and the micro closer to the bottom of the board, making room for the power LED and resistor near the capacitors. Make sure you add 0.1uF filtering caps near each block of 3 pin connectors and near the H-bridge. In theory, all ICs and group of connectors should have a pair of 10uF and 0.1uF close by. Other than that, I can’t offer help, as I don’t know how Picaxe works.
One more thing, it is a good practice to have the signal pins in the 3pin connectors allways close to the microcontroller, instead of the GND pin. Most boards respect this pattern, I think it will be a mistake to change it. Oh, and routing the motor connector trace between the microcontroller pins is NOT a good idea. Think of how much electrical noise can screw up your readings or even the microcontroller functionality. Move them away from anything delicate!
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.
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.
Open question: Advantages, disadvantages of a power plane (5v) on top? I used one on my LCD back pack and it is good for cutting down on traces like the GND plane, but I do not know if it adds noise or if you need some good filtering. Mine seems to work fine.
wikipedia:
Where possible it is good to have a power plane for each ground plane on a board (known as a “plane pair”), as this reduces power supply impedance to the components on the board.
Asked an electrical engineer online friend and he said no problem that he knows of. So a power plane like this might be helpful if you want to cut down on traces or change things around.
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.
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.
