best practise for wiring heat bed via sevenswitch

I have a Sanguinololu 1.3a. For connecting the heat bed (PCB Mk2) I have built a seven switch using the pcb from Traumflug, because apart from the dimensioning of the mosfet and the connector I was a little bit concerned about routing the heat bed current through the sanguinololu board at all.

Now, the seven switch just needs the (pwm) signal for the heat bed and ground. The obvious solution would be to de-solder the heat bed mosfet and replace it with a connector so I can get the signal to the seven switch.

However, I was wondering if there was a less intrusive solution, like using another pin somewhere on the board which is accessible and can be enabled in the firmware accordingly. I am asking because I don't feel really comfortable with desoldering the mosfet from the board (the board was pre-assembled from the UK and I have so far never (de)soldered lead-free - supposing the board has been assembled using lead-free solder).

Edited 1 time(s). Last edit at 04/25/2013 04:54PM by Stemer114.

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However, I was wondering if there was a less intrusive solution, like using another pin somewhere on the board which is accessible and can be enabled in the firmware accordingly.

Sure, do this. While PWM-able pins are prefered, any digital I/O pin will work. Most firmwares don't do PWM on the heated bed anyways.

Regarding which pin exactly ... well, you have the board in front of you, so you can look at it much better than me :-)

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

OK, for anyone interested, following Traumflugs suggestion I had a look at the schematic and selected the PWMPB4-pin (on the extension pin header) on the Sanguinololu and connected it (and ground) to the sevenswitch signal input. Then I adjusted the DEFINE_HEATER for the bed to PB4 in teacup firmware config.h and flashed the firmware. I hoped this was safe because PB4 doesn't use timer1, although it was not listed as a pwm-able pin.

After connecting the heat bed to the seven switch and powering the seven switch with a free molex power connector from the power supply and rechecking everything it was time for a smoke test, which was negative (ie no smoke).

Then I powered up the sanguinololu and tested selecting different heat bed temperatures, gradually increasing up to 100 °C - which worked right away.

And without any soldering on the sanguinololu...

PS. using the KTY 84-130 temperature sensor which was more readily available for me (from Reichelt) and it seems to be working ok for the heat bed (with adjusted firmware thermistor tables)

Edited 1 time(s). Last edit at 04/28/2013 05:40PM by Stemer114.

Sounds like a full success. Great!

I took the freedom to put a note on this into the RepRap wiki: [reprap.org]

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

To follow up on this: Connecting the heat bed via PB4 freed up the original heat bed connection and its 4-pin header, which I have used to connect two 40mm cooling fans for slic3r/firmware-controlled cooling the workpiece while printing.

This has been running now for a couple of weeks and seems to be working well, as I have gone from printing blobs, then calibration objects, then spare gears (just in case), then a guidled idler for the extruder (http://www.thingiverse.com/thing:18379) , on to Mendel90 plastic parts - with the odd minecraft pick-axe thrown in between for my kids..

To summarize: Sanguinololu 1.3a, heatbed is connected to sevenswitch via PB4 via extension pin header, two small fans are connected directly to the original (mosfet driven) heatbed connector and can be controlled by the slicer/extruder. What I like about this solution is that there were no hardware changes at all required on the sanguinololu.

In Repetier firmware pins.h, the pins are FAN_PIN set to 12 and HEATER_1_PIN set to 4 for the fans and heat bed, respectively.

@ Stemer114... how do you control the temparature using slicer/extruder software??

I am using RAMPS1.4, built a seven switch but I am not sure from where to take the +12v supply..... from RAMPS D8 or ext PSU?

If RAMPS then will it cross 11 A to heat the heatbed? OR

If ext PSU then how will be the temprature controlled using slicer software?

-Prashant.

Hi,

I have selected pin #45 to use with Seven switch.
The command would be M42P45S255
But how do I use this.... Do I need to enter this command in the gcode file manually or some other way...?

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prashantdshinde
@ Stemer114... how do you control the temparature using slicer/extruder software??

I am using RAMPS1.4, built a seven switch but I am not sure from where to take the +12v supply..... from RAMPS D8 or ext PSU?

the heatbead temperature is monitored via the second thermistor input of sanguinololu board, therefore it can be controlled without any configuration changes and should pretty much work with any firmware and host controller. I am using Repetierhost with Repetier FW and can simply enter the target temperature therein (under tab manual control). This then sends an e.g. M140 S60 command to the printer/firmware. This is independent from the slicer, I only control the heat bed temperature manually.

The idea with seven switch is to keep the heat bed power away from the sangiuno. Sanguino only shares a ground and a signal line with the seven switch for the heatbed. So the 12V for the heatbed should come from the PSU via sevenswitch to the heatbed. YMMV for RAMPS, though..