On Thu, 1 Apr 2010, Andy Pugh wrote:
Date: Thu, 1 Apr 2010 11:59:53 +0100
From: Andy Pugh <[email protected]>
Reply-To: "Enhanced Machine Controller (EMC)"
<[email protected]>
To: "Enhanced Machine Controller (EMC)" <[email protected]>
Subject: [Emc-users] Resolver Feedback. SPI communication?
I had an eBay "accident" last night and I have bought 3
resolver-feedback servos.
Looking at ways to drive them, I have found the Analog Devices
AD2S1200 chip, which basically connects to a resolver and outputs the
position and/or velocity as simulated quadrature encoder, 10-bit
parallel and 3-wire serial.
The ICs are not inexpensive at £24 from RS, though I have found a
couple on eBay if any of the US residents fancy a fiddle.
http://cgi.ebay.co.uk/AD2S1200-Resolver-to-Digital-Converter-w-Oscillator-2_W0QQitemZ390176423077
I suspect that the Pico and Mesa resolver boards use the same IC,
though it is hard to be sure from the photos :-)
We dont use that chip, we use 1 MS/Sec 12 bit A-D as part of a oversampled,
synchronous (to carrier) DAQ system in the FPGA. Partly because we wanted to
retain the absolute position capability, and partly for cost reasons.
Anyway, the point of this is to wonder what the status is of SPI
communications in EMC2. That seems like the ideal way to get the data
back from such a device, but all I have found on the WIki is a page
set up for the development of a Hostmot2 SPI driver, and that seems
not to have been updated. Is there anything in the pipeline or already
available that I have missed?
There is no current SPI support in the driver but the SPI firmware is
available. For simple SPI tasks, HostMot2s raw-read-raw-write capability can
be use in a comp to access SPI peripherals
One use for SPI or I2C might be to drive various motor controllers
with one of the inexpensive digital potentiometer chips, which seem
like a very easy way to get -10V to +10V output from a digital data
line.
After a bit of looking at stock lists I have found something which
might be easier... There are 128-step digital pots that take an
up-down pulse train. I think you could drive one of them directly from
a stepgen? Datasheet:
http://docs-europe.origin.electrocomponents.com/webdocs/077f/0900766b8077ffdc.pdf
I think SPI would be easier (because a large analog step would require a quick
counted burst of pulses, not something the stepgen is designed for)
--
atp
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Peter Wallace
Mesa Electronics
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