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What MCU are you using? If you're using an MCU with 2 UARTs you can dedicate one UART for UART/communications functions and you can re-program the other UART as an I/O port to do your bidding.
I would be limited to using a maximum of 3 servos
Not necessarily: the $50 robot doesn't use several of the pins at the bottom left of the chip. Ok - so you need to add some extra header pins to the board. But the only thing you need to decide is: are they driving servos/motors in which case they need to use the motor supply, or will they be used for digital i/o in which case they need to be connected to the +5v from the voltage regulator. The board assumes that all your inputs are 'analogue' which is not always the case with things like a Sonar which switches between being an input and an output but must be connected to the TTL supply line.I find this to be the major headache when making a board. You have 2 supply rails: TTL and Servo/Motor - so you need to decide which pins will be used for what. IMHO - it would be great if the $50 robot could have one 'nicely smoothed' supply that could be used both as a TTL input or as a Servo or TTL output.
Thats whay there are 3pin headers all around the outside of the board. So they MUST(?) be using a common +ve supply voltage irrespective of whether they are driving motors or acting as digital I/O lines. Maybe that's why that great big capacitor is there? Admin?
If I added headers to the unused pins, they could be used the same way as the pins for the servos?
Does anyone have any examples of how they have utilized their $50 robot board beyond the SoR tutorials?
Just tell us what you want to do, and we'll show you how. If you can output a signal for servos, and input a signal for sensors, and can do UART, you've learned 90% the concepts already.
MHO - it would be great if the $50 robot could have one 'nicely smoothed' supply that could be used both as a TTL input or as a Servo or TTL output.
The outside header row all around the board is ground. For the ADC pins, its a regulated 5V, while the other power pins (such as for servos) is unregulated. And the inner header rows are signal pins.
but is everything else on the unregulated power supply? In which case:- if you are using a 'digital' sensor, like a Ping or Devantech Sonar, or a digital infrared sensor, or a bumper micro-switch then you need to connect it to an ADC port so that the power supply is correct and hence waste an ADC pin? Just trying to understand....