Changing to a thermcouple is a near future project for me, too. The MAX chip looks better for this application, especially since I'm looking at nylon and maybe PC printing (300-320C range).
For this, the AD595 has a couple of issues. First, the output for the termperature range I'm looking at is 3 to 3.5v, which is over twice the range of the BBB's ADC. The voltage divider is easy, but by the time I've added in a safety zone and add something to limit the voltage into the ADC, it becomes more complex and results in lost resolution. Also, the max chip can run on 3.3v that the rest of my BBB uses. The AD595 would probably require something above 5v to measure the temps I'm looking for. What I haven't decided upon is where to mount the converter. Can the thermcouple wire withstand the repetitive motion if the extruder were to move relative to the converter (on the X and Z axis), or should it be mounted near the extruder so that the thermocouple wire doesn't get flexed at all? On Fri, Aug 9, 2013 at 9:11 AM, Charles Steinkuehler < char...@steinkuehler.net> wrote: > On 8/9/2013 8:59 AM, Andrew wrote: > > Hello, > > > > I recently got a 3D printing head with K type thermocouple off ebay. > > There are two kinds of converters for these thermocouples: > > - AD595 with analog output 10mV/C, > > - MAX 31855 with SPI output > > http://datasheets.maximintegrated.com/en/ds/MAX31855.pdf > > The first type needs ADC (which I already have in 7i73 as the last > resort, > > but I would not like to use it for 3D printer). > > Thus the SPI type looks preferable. But is it compatible with MESA > sserial? > > Or (even better) with Beaglebone? > > If the SPI pins are free you can probably use it pretty easily with the > BeagleBone. If you want to talk to it via real-time HAL you'll have to > write a low-level SPI driver to talk directly to the hardware, but > that's probably not necessary. > > I use the on-board ADC for my thermistors, and have a python script that > uses the Linux kernel driver for the ADC to grab the value and then > convert it into a temperature that is injected into HAL. It's not real > fast or hard-real-time, but that doesn't matter much for a temperature > control. > > There are kernel drivers available for SPI as well, but I haven't tried > to use them. IIRC the guy making the Replicape uses the Linux SPI > drivers, so there's probably something on his blog about getting it > working to get you started...yep, here you go: > > > http://hipstercircuits.com/enable-spi-with-device-tree-on-beaglebone-black-copy-paste/ > > -- > Charles Steinkuehler > char...@steinkuehler.net > > > > ------------------------------------------------------------------------------ > Get 100% visibility into Java/.NET code with AppDynamics Lite! > It's a free troubleshooting tool designed for production. > Get down to code-level detail for bottlenecks, with <2% overhead. > Download for free and get started troubleshooting in minutes. > http://pubads.g.doubleclick.net/gampad/clk?id=48897031&iu=/4140/ostg.clktrk > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > > ------------------------------------------------------------------------------ Get 100% visibility into Java/.NET code with AppDynamics Lite! It's a free troubleshooting tool designed for production. Get down to code-level detail for bottlenecks, with <2% overhead. Download for free and get started troubleshooting in minutes. http://pubads.g.doubleclick.net/gampad/clk?id=48897031&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
