HBP thermistor connection

[chapulina]

Hello there!

So I've been trying to build my own HBP from scratch... I'm almost
done already but I have a probably dumb question before I finish it
up...

So I put together some thin aluminum plates until I had about a 5mm
thick 100x100mm plate. I covered it with kapton tape on both sides,
put about 3.8 ohms of Nichrome and a thermistor on one side and
covered it all with more kapton tape.

I know I should connect the nichrome to the B port of the extruder
controller, but where should the thermistor go? And should I add a
little circuit around it or can I connect it directly to the bot?

Thanks in advance for the help!

[makerman]

I build my own too. If you have a cupcake connect the thermistor to
the A6 port.
Use the two outside pins and twist the wire to the HBP.
Connect the heater to the A port. B is used for the extruder heater.

Perhaps the resistance 3.8 ohm is a bit low, it wil draw 3.2 Amps.
Use a relay or replace the FET's on the extruder controller.
I use IRF 3205. They were cheap. Only replacing is a bit akward.

Use counter sunk bolts if it possible with your aluminum platform.
Btw. my platform is 110 X 110 mm.

[Whosawhatsis]

You will need a small circuit in addition to the thermistor. At a
minimum, you will need a resistor. I'm not sure of the value off the
top of my head, but it should be somewhere in the 10K range, give or
take a zero. This will be used to create a voltage divider, with one
of the spare analog pins connected to both 5V and GND through
resistors, one of which is the thermistor. Check out the schematic for
the MBI board for specifics: http://www.thingiverse.com/thing:2041

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[chapulina]

Thanks for the replies!

Yeah A port! I don't know what I was thinking when I said B ><

I really have no idea of what I'm doing so I wanna make sure I
understood it all right. The schematics on Thingiverse include a 4.7k
ohm resistor and a 100nF ceramic capacitor, but I should be able to
get away with just the 4.7k ohm resistor, correct?

A6 has 3 pins coming out of it, from the top: GND, 5V and SIG. The
thermistor goes from GND to SIG, and the resistor goes from 5V to SIG.
Is this it?

Thanks for the patience ^^

[Matt Smollinger]

Are you on Gen3 or Gen4 electronics?

I ask because Gen3 you will probably want the capacitor. The MOSFETs
on Gen3 don't handle instant power draws well at all, and if you're
gonna be pulling 3 Amps at 5v, you'll be pushing that thermistor
circuit hard. I think adding the resistor in line will drop it, but I
wouldn't wanna test it without the cap. Gen4 should be better as MBI
redid all the MOSFETs on it.

--MS--

On Aug 17, 10:01 pm, chapulina <burajiru.no.chapul...@gmail.com>
wrote:

[James McCracken]

I built my own HBP. I created a little circuit with a 4.7K resistor
and a capacitor (actual value probably doesn't matter greatly - it's
to smooth out the spikes slightly - it creates kind of a "rolling
average" of the reading) and its been working almost a champ ever
since.

I say almost because it stopped heating up a couple weeks ago - I
suspect a bad wire connection... make sure to crimp + solder those
heater wires!

[chapulina]

I have Gen3 electronics... I'll use a capacitor too then :) Should I
just connect it parallel to the resistor?

Thanks!

[makerman]

On Aug 18, 3:19 pm, chapulina <burajiru.no.chapul...@gmail.com> wrote:
> I have Gen3 electronics... I'll use a capacitor too then :) Should I
> just connect it parallel to the resistor?

I mounted the 4k7 resistor on the extruder controller. Then you have
only two wires to the platform.

A6 has 3 pins coming out of it, from the top: GND, 5V and SIG. The
thermistor goes from GND to SIG, and the resistor goes from 5V to SIG.
Is this it?

Yes.

The capacitor I used is 10 nF near the HBP. Don't use an electrolytic
capacitor here. Ceramic is OK.

[chapulina]

Thank you so much for the help, guys! My HBP is working relatively
well now :) I still have a few problems but I should be able to solve
them soon ^^

I summarized what I did on my blog, if you are interested in seeing
pictures.

http://myshumi.posterous.com/heated-build-platform

Thanks again!