Chamber heater on the Duet

I intend to install a chamber heater on my new printer driven by a Duet 0.8.5 board without extension.
I prefer to use the Duet than an independant controller as with the chamber thermistor connected to the Duet, that may improve the safety and this can be directly managed from the web interface.
Pins for other extruders (3,4,5,6) are available on the extension connector, with not conditioned signal.

I/ Connection on the board
a/ get the temperature: I have to add a resistor for measurement. Duet schematic also show a capacitor (decoupling ?) Is there some minimal board for this ?
b/ I shall relay the heater (230V). A standard sharp SSR need 8mA to be triggered, which I assume being too much for the processor.
I found board relays for the Arduino, which only needs 3mA for triggering. Could such a board be used directly? - Duet is 3.3V while arduino is 5V - Also my VCC is 24V
an example : [www.amazon.co.uk]

II/ How to tell the board/web interface that there is a chamber ?
I could define a heater with Gcode M563, but how to indicate that this is a chamber ?
I activated the chamber option in the web interface.js file and it show up on the screen, but I did not found how to declare the heater corresponding to the chamber.

III/ I would have liked to use spot lights instead of a heater, but that means that I have to use a angle phase controller, and I did not found a low cost angle phase dimmer which could be driven by a low frequency pwm signal. did that exists ?

Is your printer single or dual extrusion?

If it is single extrusion, then you can use the second heater channel of the Duet 0.8.5 to drive the chamber heater. Simply wire the input side of your SSR to the second heater output, and use M141 H2 in config.g to assign heater 2 to the chamber heater.

If it is dual extrusion, then you will need to use the pins on the expansion connector assigned to one of the heater channels. The active low heater output should be able to drive the negative input of a SSR-25DA directly (connect the positive input to +3.3V), because the current required is specified as 7.5mA @ 12V and will be much less at 3.3v. The same may hold for your Sharp SSR too. Connect the thermistor in parallel with a 1uF ceramic capacitor between the corresponding thermistor input pin and the VSSA pin on the Duet 0.8.5 expansion connector. Also connect a 4.7K 1% resistor between the thermistor input pin and +3.3V.

Edited 1 time(s). Last edit at 10/04/2015 01:30PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I finally found some dimmers under the research phrase 'digital AC dimmer'

1/ [www.tindie.com] - looks ok 20 Euros + 8 euros shipping
2/ [www.inmojo.com] - Safety was questioned in forum (low/medium voltage distance)
3/ [www.sunrom.com] - looks bad - poor voltage separation, poor connection
4/ [www.powerswitchtail.com] - only as a kit in 230V - probably for CE certification avoidance

I see no point in using fast PWM or dimmers for the chamber heater, because the heating time constant is so long. I suggest you use either bang-bang control for the chamber, or slow PWM (which works with DC/AC SSRs). I plan to change the bed and chamber heater to use slow instead of fast PWM in my next firmware release.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
I see no point in using fast PWM or dimmers for the chamber heater, because the heating time constant is so long. I suggest you use either bang-bang control for the chamber, or slow PWM (which works with DC/AC SSRs). I plan to change the bed and chamber heater to use slow instead of fast PWM in my next firmware release.

Dave

That is interesting looking forward to that release.

On a similar point are you thinking of implementing support for E3D's PT100 sensors/amplifier board?

Doug

On the one hand, anything that E3D sells is worth supporting from a commercial viewpoint. On the other hand, although PT100 sensors are in principle capable of very accurate temperature measurement, I doubt whether the E3D implementation achieves better accuracy than a thermocouple. Their web site doesn't provide enough information to tell. There is already thermocouple support in Dan Newman's fork of RepRapFirmware, which I will merge into mine when I get time.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
On the one hand, anything that E3D sells is worth supporting from a commercial viewpoint. On the other hand, although PT100 sensors are in principle capable of very accurate temperature measurement, I doubt whether the E3D implementation achieves better accuracy than a thermocouple. Their web site doesn't provide enough information to tell. There is already thermocouple support in Dan Newman's fork of RepRapFirmware, which I will merge into mine when I get time.

Good enough for me.