Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here.
One of the problems of moving from the simple three byte SSC style control system to a system where we can do clever things with multiple servos at once is that the data required to do these clever things is bigger than the data required to do the simple things.
Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here.
To be able to implement the new commands for the servo controller I need to adjust the data that we use to control the servos. Right now we have a single byte per servo and that byte contains a value between 0 and 254 which represents the length of the pulse sent to the servo.
Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here.
The 64 channel serial servo controller that I’ve been developing works pretty well for me but most of my development and testing was done in the AVR studio simulator. Once I actually started working with my hardware again I noticed a slight problem.
Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here.
The time has finally come to put all of the code from the last three parts of this article together to form a complete serial configured, 64 channel, PWM servo controller for the ATTiny2313 and several CD74HCT238Es.
Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here.
This is part three of a series of articles about the servo controller that I’m building for use in the hexapod robot that I intend to build. The first two articles in the series have presented the timer driven PWM generation code and the code used to take the configuration data that is managed by the serial port protocol and convert it into the data that is needed by the PWM generation code.
Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here.
In part1 of this timer driven PWM servo controller I built some code which uses Timer1 in the ATTiny2313 to generate 64 PWM signals. The code in part 1 worked from hard-coded dummy data. The code presented here shows how we can create the data that the PWM generation code needs to run.
Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here.
As I mentioned recently, the original servo controller firmware that I posted was flawed and wasn’t suitable to use as a base for the more complex servo control code that I want to add to the controller. The new firmware follows the design that I spoke of here and relies on the ATTiny’s 16-bit timer to generate our PWM signals.
Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here.
As I mentioned here, there’s a fundamental design problem with the two versions of the ATTiny2313 servo controller firmware that I’ve presented so far (see the 8 channel source code and the 64 channel source code). The timing that determines the shape of the PWM signals that are generated relies on carefully crafted timing loops and the time taken by particular code sequences and this is affected by the interrupt driven serial I/O that is used to control the controller.
Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here.
In my opinion there’s a fundamental design flaw in the both the 8 channel and the 64 channel servo controller firmware that I’ve presented. Both allow the serial data handling code to take priority over the PWM generation code.
Previously published This article was previously published on lhexapod.com as part of my journey of discovery into robotics and embedded assembly programming. A full index of these articles can be found here.
Here’s the source code to the 64 channel ATtiny2313 servo controller. Note that you’ll need to use up to 8 CD74HCT238E, or equivalent, demultiplexer chips and that you can adjust the number of servos that you can control in steps of 8 using as many or as few CD74HCT238E chips as you want.
