Huxley heatbed connect to Ramps 1.4

Hi all.

Upgrading my Huxley from Melzi to Ramps 1.4, in order to add a second extruder.
Slowly getting my head around the Arduino software; the printer seems to be working, it moves and the hotend heats etc.

My current difficulty is connecting the Heatbed. Ideally, I want to use the mosfet so I can run it from the stock 19v PSU. I've tried connecting the mosfet control wire to the heatbed connector on the Ramps (pin 8?) but no dice.
Can I connect it to another pin and get it to work that way? Modifying pins.h I assume... How? What? Where? Why? When?

If not, I believe I need to move the jumper wire on the bed PCB and connect to the outermost power connectors (+ve and normally nc). Will this work? How badly will I suffer from 12v vs 19v?

EDIT:
Ok, well out of desperation I tried the second option. It works, but my god is it slow! it's taken nearly 5 mins to get to 45 deg - unusable. I could really do with some help on this.

Kind regards,
Michael.

Edited 1 time(s). Last edit at 07/12/2014 02:50PM by rainingheavy.

To use the heated bed mosfet:
- connect the control wire that would normally go to the AUX header on Melzi, to AUX 4 header on RAMPS, on pin 18 (last one), which corresponds to D16: you can use any other digital pin that is available on an AUX header; however, it is recommended to use one that could not be used for other purposes;
- in pins.h change the HEATER_BED_PIN assignment appropriately:
from
#define HEATER_BED_PIN 8
to
#define HEATER_BED_PIN 16
assuming you have an Arduino Mega

Hi,

This is exactly what I was after, however, I also use the LCD (it's the sainsmart ramps kit with lcd etc. - but no microstepping jumpers! > )
I have the I2C pins free (4 next to endstops), the unused max endstops, or Aux1 and Aux2 which need header pins...
How do you know which pin is which? I assume there is a pinout diagram, but I've struggled to find it...

Cheers,
Michael.

[reprap.org]

And in pins.h the assigned number is the number of the D-igital (or A-nalog) pin. For example, #define HEATER_BED_PIN 16 assigns pin D16.

You can use the I2C pins SDA/SCL, which correspond to D20/D21, but you have to make sure I2C function is not activated by default (which I assume is not, but you should better check) in Marlin.

Edited 1 time(s). Last edit at 07/13/2014 02:43PM by 3Dmaker4U.

Hi,

Thanks, that helps a lot. I'll be sure to let you know when it works.

On another note, rather than starting a new thread, what thermistor settings should I use; stock huxley thermistors.
I found somewhere that mentioned the bed thermistor code, and number 8 matched, but the temp reading was wrong. (9deg instead of 26ish)
Using number 1 I have them reading a number that works, but I feel like it's not right. I can't make heads or tails of the RepRapPro Marlin settings; it seems to reference the serial resistor, but what and how that affects I don't know...

I need to get a new IR Thermometer...

Anyway, thanks for answering the original question.
Cheers,
Michael.

Well, stock might change

If you take into account the information on the same instruction page about commissioning of a Huxley

echo:Thermistor settings: M304 Hh Bb Rr Tt, H0=Bed, H1..n=nozzle, b=thermistor beta value, r=series resistor, t=thermistor resistance as 25C
echo: M304 H0 B4200 R4800 T100000 M304 H1 B3960 R4700 T100000

it means:
for bed (H0): Beta=4200, with a resistor of 4800 ohmi (peculiar value, might be to "compensate" the change of the "standard" 8 type, which has a Beta value of 4100)
for nozzle (H1): Beta=3960, with a resistor of 4700 ohmi

You should first see what is actually the firmware reporting to you, but on the original Melzi with the RRP firmware. Issue a M501 command, and identify the lines similar with the above. Then find datasheets for the thermistors defined in Marlin and identify which one has the closest Beta value.
RRP uses their own Marlin version that does not rely on the thermistor table, but rather on the thermistor parameters (resistance at the reference temperature, which is 100 kohmi, and Beta, which vary from one type to another) to calculate the resistance at a given temperature.
If you switched to a "pure" Marlin version, then you have to identify the thermistor as described above.

Thermistor type 1 (EPCOS - B57560G104F), has a Beta value of 4036.
Depending on the value reported by the firmware (via M501), you can try to figure out why the indicated temperature is not as expected.
You can also measure the resistance between the thermistor each thermistor wire and +5V (Vcc). The value around 4700 ohmi should be the resistor value.

It would be more difficult to identify the thermistor type if you cannot count of the original firmware information. What you can do is to try to determine the Beta value using some measurements and the formula that links the actual resistance, Beta, nominal resistance and temperature. If you use an IR thermometer, make sure to spot on the center of the plate (the gradient to the edges could be of several degrees).

Well, it's not necessarily about heads or tails, but you have to step by step clarify all elements that could make the difference you see/guess

Thank you,

I should be able to work it out now.

Cheers,
Michael.

Quote
3Dmaker4U
[reprap.org]

And in pins.h the assigned number is the number of the D-igital (or A-nalog) pin. For example, #define HEATER_BED_PIN 16 assigns pin D16.

You can use the I2C pins SDA/SCL, which correspond to D20/D21, but you have to make sure I2C function is not activated by default (which I assume is not, but you should better check) in Marlin.

Finally got 'round to sorting this, and would you believe it; it works!

Heatbed setup as stock, with the MOSFET pin connected to RAMPS pin 21. Stock 19v PSU dedicated to the Heatbed (and hot end fan).

Once again, thanks.

Michael.

Hey,

I know I'm coming in way late on this conversation but I just recently had the same issue myself. The little wire jumper soldered into the board has two ways it can go in. One way connects the mosfet and therefore works nicely with boards like the Melzi. If you switch that jumper to the other side, you will allow for a power input that goes straight to the heater. You can no longer plug power straight into bed but instead, run your D8 wires straight to both of the outer green terminals.This is the simplest solution I have because it utilizes the mosfet on the ramps shield itself without the need of anything extra. At this point, you are left with just four wires between the bed and the ramps board, two for the thermistor and two for the heater wires.
Hope this helps as an alternative.