I’ve been working recently on the next generation of electronic hardware for the energy plotter. The main changes are that we’re now using proper stepper drivers instead of a ULN2008 and the RFM12 radio modules instead of Xbee.
Proper stepper drivers allow us to do current limiting on the motors, so we can set a current for driving and change this in use for each motor. This is great for efficiency, as it allows us to turn down the holding current when we’re not moving the motors. It also lets us do an easy homing algorithm like this one.
The RFM12 radio is about a quarter of the price of the Xbee and we don’t lose any functionality. Another advantage is that as the open energy monitor crew use the same radios, I hope we’ll start being able use each other’s kit.
The new version of the hardware will also incorporate 2 wire servo control for pen lift via the gondola wires.
We’re looking at incorporating an SD socket for those who want to use the polargraph to draw pretty pictures. This may now be possible to fit onto the microcontroller chips we’re using because Sandy (over at polargraph.com) found this small FAT library.
We’re also looking at incorporating a serial USB connection (instead of the easier FTDI) on the board for software updates and direct computer control. We can do this with some of the new Atmel chips, or possibly use a minimus for the entire controller.
Finally, we may be moving to a “cloud” based solution for drawing and logging. For example, energy (or any other data) is logged to cosm (my energy feed is linked). Another service pulls this data as it happens and runs it through and algorithm to generate drawing commands. These are sent back to the polargraph. This makes it easier for infographic algorithms to be developed as the artist can preview the output with many people’s data streams. It also means we don’t have to worry about fitting complex algorithms into the tiny processor on the polargraph. Instead the server does all the work and sends super simple drawing commands. If logging and environmental drawings are not required, the polargraph can be driven directly via a local computer (or possibly an SD card).