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AD595, multiple thermo couples and digital switches

Posted by slzer 
AD595, multiple thermo couples and digital switches
June 17, 2015 11:05AM
So i recently purchased a Dual extruder for the 3d printer and typically I didn't notice that it used thermocouples not thermisters. Thus was not directly compatible with my RAMPS 1.4 board.

I found solutions online which use either the AD595 or MAX31855 to connect to RAMPS 1.4 (both of which are supported by the Marlin firmware) but both these chips are quite expensive and as such the costs build up pretty quickly for a dual extruder setup. Also none of the breakouts have been designed such that they fit straight onto the AUX parts of the RAMPS board. Looking at the two solutions I wasn't a fan of the MAX chip with SPI because you would need to connect it up under the SD card connection I use for the full graphics display which has an SD card slot included.

So the AD595 only needs 5v, gnd and one analog port meaning it could be used on AUX1 which wouldn't interfere with the SD card. But the problem remains for a setup with multiple thermocouples it is going to get expensive if we use one chip for each thermocouple. So it got me thinking could I not use something like this quad bilateral switch (50p) to simply change between the thermocouples and use a single AD595 chip (£7 or so per chip). You could use 3 of the aux pins (D1, D2, D58) and then A3 for the input. then 5v and Gnd for the power. leaving the other 5v and gnd pins unconnected.

Anyay this would mean a possible 3 thermocouples could be interfaced with using a breakout that would probably cost <£10 rather than having to use 3 seperate ones which are £7-8 each

Anyway i'm not an Electronics expert in any way so I need some advice to whether this would be feasible or not?

Edited 1 time(s). Last edit at 06/17/2015 11:07AM by slzer.
Re: AD595, multiple thermo couples and digital switches
June 17, 2015 12:24PM
You would only read one thermocouple at a time and have to provide some signal to switch between the inputs.
Also the AD595 has a signal_lost cable control alarm, that might get triggered while switching..

If it is too much trouble to get a thermcouple running, can´t you just replace them with thermistors in the hotend and be done?
Re: AD595, multiple thermo couples and digital switches
June 17, 2015 12:26PM
I've ordered some AD595 breakouts for now but it was more of a prospective thought because allot of the all metal hot ends come with thermocouples installed
Re: AD595, multiple thermo couples and digital switches
December 03, 2016 05:58PM
I know this post is older but did you get two thermo connected on ramps?
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