to receive data from Dynamixel servos using the Dynamixel Serial library.
However, upon reviewing the schematic of the shield:
it seems that the connection to toggle between transmit and receive has been wired directly to the 3.3v pin which, as far as I know, cannot be toggled in software.
I'm thinking of removing the 3.3v connector between the shield and arduino and delivering 3.3v to the shield pin in a way that is switchable to allow for transmit and receive.
Under software control? Add a transistor. Does it need much current? Pull it up to 3.3V with a resistor, and use a transistor to pull it low. Or a uC output pin if it's just a signal level.
Using a uC output pin would be easiest, I'm just unsure if any of the components are 5v intolerant and whether the designers used the 3.3v pin for a reason.
With a transistor I'm assuming I would use a uC output pin on the base for switching. Wouldn't it cause problems for the base voltage to be higher than the source(3.3v)?
With the uC and a pullup to 3.3V, you'd be all set.
Leave the uC pin as in Input for 3.3V, make it a low output for a low. Don't drive it high as an output, then it will never have 5V on it.
With an NPN, you are driving current into the base to turn it on to sink current from collector (3.3V pulled up at the shield) to the emitter (at Gnd).
You will have a current limit resistor between uC and the base, the base by design acts like a diode connected to the emitter and doesn't go above ~ 0.7V.