Is it possible to hack the 1.31 board to have the thermistors always on?

Now on the 1.4 board the thermistor circuits are powered by 5V standby, so firmwares like marlin and sprinter which do a sanity check don't throw an error. The only workaround as of now it to jumper the atx supply (jumperwire green to ground).
if it would be possible to cut a trace and solder a wire to power the thermistor circuits with 5Vstandby on a 1.31 board some people might choose not to upgrade/ sure you loose out on extension capabilities, however this hack would be good for those of us that currently don't have the funds to spare to upgrade.
it should be a simple matter of cutting a trace and adding a wire from the 5Vsb supply.
Could we get some instructions? or comments why it would not be a good idea?

terramir

Edited 1 time(s). Last edit at 07/13/2012 03:08PM by terramir.

[forums.reprap.org] and [forums.reprap.org]

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

this looks like the ground fix how would this keep the power always on to the thermistors I'm not sure but I wanted to fix it so the thermistors work even though the psu is off (i.e. powered by 5vsb) but I might be worng here, but then again they both look like the same link once opened, maybe somethings messing up in my web browser
terramir

The thermistors should be powered from the AVDC pin on the micro with a track that is not shared, otherwise you get inaccurate results.

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[www.hydraraptor.blogspot.com]

so still what I can't figure out this hack right there wasn't that the ground fix that solves various problems, however this is not what I was looking for, what I was looking for was a hack in regards to the powering of the thermistor circuits. I need them always on i.e. powered by 5v vsb, currently on the 1.31 board they are turned off i.e. reading out of range unless the power supply kicks in (so you have to jumper the power supply in marlin and sprinter (green to gnd hack) I want to make them read all the time.
can someone chime in on this and explain to me a little further, cause if I follow the tracks right there in this hack it just seperates the ground planes while this might help with accuracy it still wouldn't turn them on when the power supply is not triggered.
terramir

You have to hack the connection to the resistors and connect it to the AVCC pin on the micro. It both makes them active whenever the CPU is powered and also improves the accuracy.

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[www.hydraraptor.blogspot.com]

can you put that in a picture of the 1.31 circuit so I can understand what pins that is going to be ?
I should be able to take it form there
although a write-up for other gen7 owners might be nice as well so they can do this too.
terramir

so just curious would this work the black marker is the cuts and the green would be wires since the atmega is connected to standby or other power options through a jumper I thought this would be the logical place to tap the power from, also added the ground hack
peeps I could use some verification before I got cutting the traces on my board

terramir

No the resistors should be connected to the AVCC, pin 30. It is also powered from VSB via L1.

I think the ground cut should be near C7, not where you have it.

The mods have been published in this forum before, see [forums.reprap.org]. What I don't understand is that that picture also shows V1.3 but it doesn't look like yours. Also it doesn't look like these mods are in the latest V1.4.

The ADC takes its reference voltage from AVCC. The thermistors should be biased from the same voltage so that any supply voltage change is cancelled out. Also thermistor ground should not share traces with power ground. They should starpoint near to the CPU GND pins so that ground current does not cause a voltage offset.

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[www.hydraraptor.blogspot.com]

Nophead the board photo in the link is a 1.1 or 1.2 it has a fan header as well as an i2c header both which are missing from the 1.31 board
the ground hack I was doing I did incomplete Job isolating both the atmega and the thermistors from the power mosfet circuits
maybe this would be better:

maybe this would insulate from ground surges a bit more since the direct connection both from the mosfets to the atmega and the thermistor circuits would be broken
terramir

Yes that looks good although it is probably not a lot different to making one cut at C7 and putting the link to ground from the 24way to the mid point between the ground pins making a star point.

Edited 1 time(s). Last edit at 07/14/2012 05:19AM by nophead.

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[www.hydraraptor.blogspot.com]

So do it like this ?
is that right?
which would translate to like this on the pcb it would actually be one more cut on ground because this goes around

terramir

Edited 1 time(s). Last edit at 07/14/2012 05:55AM by terramir.

Yes that should work.

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[www.hydraraptor.blogspot.com]

Thanks for the help, nophead. Thanks for the pictures, terramir. It's in the wiki now: [reprap.org]

Edited 1 time(s). Last edit at 07/14/2012 08:59AM by Traumflug.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Did this, and it works perfectly. Thanks!

lol you did this before I did ANd I brought up the subject lol

great will probably do this in the next few days myself
no more marlin errors
terramir

Hi,
I come to "hack" my Gen7 1.3.1 board as you indicate in this thread (my board is reversed compared with the Terramir's photography but not too hard to recognize the good areas ) and it is working perfectly : now i can read the temperatures without sending a command to awake the board.
Thank you very much for your sharing.
Regards,

Thierry

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Prusa V2 + Ramps 1.4 (Marlin Firmware) avec autolevelling bed, écran LCD et alimentation à 24V + Raspberry Pi Model B (pour impression autonome) / Pronterface + Slic3r sous Ubuntu 14.04 / Niveau : Pratiquant / Localisation : Lézignan-Corbières (Aude, France)

your welcome, and thanks to nophead for the info I learn alot thanks to him
terramir