Controlling heated bed with Rapman 3.1 Electronics

[Jason Miles]

As with many other BFB printer users, I think my main issue with my Rapman 3.1 stems from warping due to not having a heated bed.  While there were probably thousands of posts related to heated beds on the old BFB forum, I was never able to find an answer to my one major question about the upgrade.

How do you guys control the temperature on your heated beds?

It seems like it would be easy enough to control the heated bed with the empty extruder 3 connections and while BFB was still updating the Rapman 3.1 firmware it seemed like we were well on our way.  I had not been on the BFB forum for some time but when I was thinking of setting up a heated bed I originally posted my question here.  Unfortunately my questions went unanswered and my prototype heated bed did not really work so well.

With a new forum I thought I would pose the question again just to keep the info readily accessible.

The most recent firmware download for rapman 3.1 (V 4.2.2) does not include the release notes (do these exist?) and it also does not include a heated bed version.  However V 4.4.1 does include the release notes and a heated bed version.  Has anyone experimented with this firmware version?

My questions are:

1. Is the heated bed firmware for double or single headed rapmans?  I would guess based on the following comment in the release notes that it is for double headed printers "Added heated bed functionality for RapMan which allows extruder heater 3 to switch on simultaneously with extruder heater 1 or 2."
   
2. What resistor should be connect to pin 22 so that the firmware knows it is a heated bed? 300 ohm?
   
3. I presume a relay circuit will be needed to supply sufficient power to heat the heated bed.  Does anyone have a schematic for this circuit?

If anyone has the answers to these questions I would greatly appreciate the help.

Thanks,

Jason