This circuit implements the Half-Duplex serial interface needed to properly communicate with AX-12 Dynamixel servos.
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I'm currently powering the servo's from the Arduino Mega's VIN connector. Although these servos can draw a considerable amount of current they typically don't unless they are under a significant load (which they're not in my project). I'm powering the Mega with a 9 Volt 1 Amp power supply.
It looks like this board will work okay with 3.3V micro-controllers like the Raspberry-Pi as well. The logic IC's only need 2V to operate. So far I've only tested this board with 5V micros.
Interesting, I also currently need this. You seem to have copied the reference design which probably is a good idea. Any reason why you have not include the decoupling capacitors for the two 74HC ICs?
The schematic from the AX-12 documentation didn't show decoupling capacitors. Based on my testing, they are not needed. I've been unable to test my communication error reporting code thus far because I haven't encountered even a single comm error yet. :-)
They have probably been just left out for simplicity. I'm not a electronic engineer, but I was told every IC a 100n, e.g. https://hackaday.com/2011/10/25/do-you-know-why-youre-supposed-to-use-decoupling-capacitors/
The circuit probably usually works without them, but they help a lot against spurious EMC related errors.
Btw I'm currently evaluating using a SN74LVC2G241 as a replacement for both ICs, any thoughts on this one?
The SN74LVC2G241 does look like a good chip to use, let me know how it works out.
It's interesting that there are a couple of Arduino libraries out there that claim to work at 115200 baud without any type of circuit conversion, they just tie RX and TX together. From reading the forums it seems results are mixed and some people get a lot of errors even though its running 10 times slower than the standard 1M baud rate.
Those Dynamixel servos aren't cheap, but they seem like a great solution for some applications. Love to see how you put this board to work. Keep us posted!
No they are not cheap but they are very high quality. The full feature set would be very difficult to implement using a simple stepper motor and gearbox. They do make a cheaper servo, the XL-320 is around $20 and seems to support the same features. They have much less torque however (about 1/4 that of an AX-12).
Jeff Wahaus
minh7a6
Mislav Breka
hariramanil810
Dave
this is a nice project! I'm trying to make a sensor using dynamixel protocol so it will act as a dynamixel sensor device using 74LS241. But the problem is when i tried read data using ping or scan from dynamixel sdk/dxl_monitor, the arduino can't read any incoming data. Do you know what's wrong?