Review of a small motor controller schematic.

[AustinSchuh]

I'm making a motor controller board for fun, and I'd like to increase the odds that it'll work the first time by having someone knowledgeable look over it before I send the board off to be fabbed. The place I'm working at this summer has a scope, hot air for soldering, some nice soldering irons, and a nice magnifying glass, so I'll be able to solder this thing up no problem. I've done some basic circuits in my circuits class last semester, but we never got past resistors, capacitors, and op-amps.

The micro-controller is a 3.3 volt LPC2101 ARM7 chip. It will be controlling 1 ~9 volt motor that stalls at 1 amp. If I remember right, the motor driver chip, a sn754410, is rated to 1 amp per channel and has 2 channels per chip, so I'm wiring both sets of control lines and outputs together to increase the output current so that I have a safety factor of 2, rather than 1. I can do that without problems, right?

I'm mostly worried that I've got the 3 regulators hooked up right, the crystal hooked up right, that I've got the LEDs set up with the correct resistors. It's easier to work on debugging the rest of the circuit when the basics work. I based all that off of other schematics that I found online, but I'm more of a ME than an EE, so I don't know if I did it perfectly the first time.

I included the 5 volt regulator to power some of the 5 volt peripherals I plan on connecting, like some nice 5 volt encoders I have. The controller says "5 volt tolerant digital IO" on the data sheet for some of the digital input pins. That means I can connect the 5 volt encoder up to one of the 5 volt tolerant pins without problems, right? Or would it be better to set up a voltage divider to step the voltage down to 3.3?

I plan on daisy chaining a number of these together, hence the two power connectors and two RJ45 connectors. They will then provide a similar role as Jaguars over CAN for FRC. I plan on implementing a bus kind of like I2C or CAN over the RJ45 connector where the bus is pulled high with a pull up resistor, and all the devices pull it down to change the bit low, and read the bit back, floating the line, to set it high. I think I've got that part set up well enough that I can deal with it later. It'll be powered using a 9.6 volt NiCad battery, so my experience says it needs to survive a sustained input of up to 11 volts.

In case anyone is looking for cheap PCB boards that sacrifice turnaround time for price, http://www.batchpcb.com/ looks pretty good. The biggest issue is the ~1 month turnaround time, but when you are a hobbyist for which time isn't an issue, it's a good way to go.

Thanks for your help!