Re: dynamixel servors AX-12
A single blink of the LED at initial powering is perfectly normal. If it starts flashing continuously, then you have a problem (usually a high temperature and/or torque overload). The Bioloid Premium kit ships with a 3S LiPo battery (11.1V nominal, 12.6V fully charged) and a 12V SMPS, so 12V is fine to use (if not outright preferred).
The 'TTL' signal level of the AX-12 is 0V and 5V for the two logical values, so you must translate the 0V to 3.2V UART of the pic to the 0V to 5V of the AX-12. The AX-12 is also a half-duplex UART, so the two buffers and single inverter are also necessary to select between transmitting and receiving instead of just being very useful in safely and easily performing the logic level translation.
If you copy the circuit as detailed in the AX-12 manual, you should be fine. You will need both the RXD and TXD pins of the UART and a third pin to select the data direction (so you only receive data when you want to and only transmit when you want to). I am thinking the buffer and inverter should be run off the 3.2V along with the PIC, but that may not be correct (does not really matter if the PIC has 5V-tolerant pins, but could cause problems if they are not and you power the buffer off 5V).
There is a way to perform the conversion from full-duplex to half-duplex on an AVR without any buffers, but I am completely unfamiliar with PIC's and whether the pins are 5V tolerant and how the internals of the UART operate. With the arbotix and similar systems running at 5V, basically they short the RXD and TXD pins of the UART together with the DXL_TTL line with a 10kOhm pull-up resistor to 5V. When transmitting, they enable the TXD functions of the UART inside the microcontroller while simultaneously disabling the RXD functions (ignores input and leaves RXD pin in the tri-state/Hi-Z mode - no influence on the pin state). When receiving, the TXD functions are disabled (set to tri-state/Hi-Z as to not influence the pin state) and the RXD functions are re-enabled to receive any data transmitted.
Last edited by tician; 04-27-2012 at 10:43 PM.
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