[quote=“ichbinsnur”]Ah, now i understand.
But are you sure the ability to drive 7mA output current would be equal to the output port resistance?
I’m not quite sure.[/quote]
Which output port?
You’re driving an analogue input pin with a 4K7 pullup.
The basic input impedance of an Atmel input pin is around 100K.
[quote=“Paul Compton”]
Which output port?
You’re driving an analogue input pin with a 4K7 pullup.
The basic input impedance of an Atmel input pin is around 100K.[/quote]
I meant the output of the thermocouple amplifier.
It must sink some current to allow the voltage to drop to its sense output (1.25v +5mV per °C)
as the Analog input line is pulled up to about 4,8 volts by the pullup resitor.
That’s why i thought it can’t work at all without removing the pullup.
The ‘sense’ pin is just the negative feedback loop for the output Op-amp, rather than connecting an external resistor to set the gain you use the precision trimmed internal one (correct gain for the thermocouple type). When sense is not connected to the output of the Op-amp, the gain is ‘open loop’ and the Op-amp functions as a comparator. A voltage applied to the sense pin then sets the ‘trip’ point of the comparator and you effectively have a thermostat.
Thanks again Paul, ans sorry, i think i mislead you.
I din’t mean the sens pin on the AD8495.
I meant the output of the breakout board, which it actually connected to the out pin of the AD8495 chip.
I’m not familliar with Op Amps right now.
But what i don’t understand is, why the Voultage output (output pin) is able to source current from the Therm2 line
dropping the voltage to the output level of the Ad8495 chip.
To be able to do this it must effectively “reverse connect” the pullup voltage to ground, or im i completely wrong here?
I just don’t understand it…
An Op-amp can source or sink current.
Both at the same time?
I just don’t get why the output can be a voltage source and drain at the same time.
I know i’m annoying, but i just want to understand it.
Perhaps i should go a bit deeper into the datasheet and layout of the amplifier board.
Good to hear that the thermocouple worked : )
Regarding the opamp output, it has a push pull circuit, with a transistor that drives and one that sinks current.
Depending on the output voltage to be delivered, either the one of the other is active (digitally speaking ; ) ).
To give you an idea of an opamp internal circuitry, here is a link to an famous one… the 741…
[quote=“RobinS”]Good to hear that the thermocouple worked : )
Regarding the opamp output, it has a push pull circuit, with a transistor that drives and one that sinks current.
Depending on the output voltage to be delivered, either the one of the other is active (digitally speaking ; ) ).
To give you an idea of an opamp internal circuitry, here is a link to an famous one… the 741…
en.wikipedia.org/wiki/File:OpAmp … abeled.svg[/quote]
Thanks a lot for the schematics Robin.
Now i got it! 
So the Op amp sinks or sources current to establish the desired output voltage, right.
If i had knewn that earlier i wouldn’t have bothered thinking of removing the pullup.
Another thing learned.
cheers
Christian
Christian,
I received my new e3d v6 hotend yesterday and it came with a thermocouple.
How do i connect that to the board?
I understand i have to buy some kind of breakoutboard like the AD8495 ?
Is that the same as http://reprap.org/wiki/ExtThermoCouple_1.0 because i can get a hand on that one quickly. The AD8495 takes a long time to ship here.
And how do i connect it to the board? I want to make as less modifications to the board so it possible i want to use the original therm inputs is that possible?
Thanks
Erik
[quote=“ErikDijkstra”]Christian,
I received my new e3d v6 hotend yesterday and it came with a thermocouple.
How do i connect that to the board?
I understand i have to buy some kind of breakoutboard like the AD8495 ?
Is that the same as http://reprap.org/wiki/ExtThermoCouple_1.0 because i can get a hand on that one quickly. The AD8495 takes a long time to ship here.
And how do i connect it to the board? I want to make as less modifications to the board so it possible i want to use the original therm inputs is that possible?
Thanks
Erik[/quote]
Can you post a picture of your “thermocouple”?
I believe it isn’t a thermocouple but a parralel wired thermistor.
cheers,
Christian
Ok, i will post a picture when i am at home.
But at the webshop i ordered it, it was clearly mentioning that the set included a thermocouple. ( http://reprapworld.com/?products_details&products_id/601/cPath/1616_1671 )
[quote=“ErikDijkstra”]Ok, i will post a picture when i am at home.
But at the webshop i ordered it, it was clearly mentioning that the set included a thermocouple. ( http://reprapworld.com/?products_details&products_id/601/cPath/1616_1671 )[/quote]
Ah, ok!
I dind’t know someone sells the actually bundled with a thermocouple.
In that case try this here : adafruit.com/product/1778
I already made a Thermistor table for it and can send you the modified frimware files.
That way you can use it right away afer connecting the Breakout board.
It works without any other modifications, directly connected to 5V power and ground and the output pin to the therm input.
cheers,
Christian
Thank you for the info.
I found a reseller that ships very fast so i hope to get the Adafruit thingy tomorrow.
I am not realy into the electronics so that 5v power and ground are that pins on the board or is in one of the small holes on the right side of the board?
And the therm input exists of 2 pins, do i connect the output pin to both of them?
If you want you can send the files to my email adress :).
Thank you for your help so far.
[quote=“ErikDijkstra”]Thank you for the info.
I found a reseller that ships very fast so i hope to get the Adafruit thingy tomorrow.
I am not realy into the electronics so that 5v power and ground are that pins on the board or is in one of the small holes on the right side of the board?
And the therm input exists of 2 pins, do i connect the output pin to both of them?
If you want you can send the files to erikdijkstra [at] hotmail dot com.
Thank you for your help so far.[/quote]
I strongly advice you to edit you last post and delete your email, or you will get tons of spam, i frear!
I Post a link to the firmware files here later.
For the +5v and GND you can use the 5v on the extension connector (small holes).
I suggest to solder in a pin header first, that way you’ll be able to connect the LCD later if you wish.
The 5v can the be tapped on that pin on the bottom side of the PCB.
The leftmost of the Therm pins (board standing upright, connectors facing up) must be connected to the output pin of the Breakout.
The other (rightmost) is ground and can be used as the ground connection for the breakout.
Make sure to measure the voltage across the pins before cou connect the ground, to prevent it from shortening.
If you measure +5v across the therm1 pins, the black probe of the mulitmeter is grounded. (as ist should)
Otherwise if you measure -5V the red probe is grounded.
If you want, i can post a picture of my connection.
I just have to disassemble my Board cover then.
If the thermocouple shows negative temp, you have reversed its polarity. Then simply connect it the other way round. (only the thermocouple, of course)
cheers,
Christian
Here is the promised link to the modified firmware.
https://dl.dropbox.com/s/am45g6oxzg5xydw/Marlin%20-%202560%20-%20LCD_modified_for_thermocouple.zip?dl=0
The thermistor type for the Adafruit AD 8495 Thermocouple-K amplifier Breakout is 70.
Take note that i use a thermocouple breakout for both bed and extruder, so you need to change
the thermistor type for the bed back to type 5.
Also note that this firmware is for the Leadscrew Upgrade (K8204), which uses a 1,5mm pich and a steps/mm value of 2133.3333.
If you have the stock M8x1.5 z screw change the steps/mm for the z axis back to 2560.
cheers,
Christian
[quote=“ErikDijkstra”]Ok, i will post a picture when i am at home.
But at the webshop i ordered it, it was clearly mentioning that the set included a thermocouple. ( http://reprapworld.com/?products_details&products_id/601/cPath/1616_1671 )[/quote]
I got my E3D for them last friday, and also noticed the thermocouple. Which took me by suprise as I expected a thermistor (expected the same contents as the original E3D kit, but this is way better).
The thermocouple is handy as I wanted to use one in the future anyway, but I did not have all the hardware for it ready.
I used the thermistor from my old hotend instead of the thermocouple instead, this way I could use it immediate.
Robin
Finaly my breakout board arrived.
With your firmware Christian it works perfectly.
One thing you forgot to mention is that you have a inverted z-motor so i had to change that too
But apart from that everything is working very smooth now.
Thank you for your help.
Regards,
Erik
[quote=“ErikDijkstra”]Finaly my breakout board arrived.
With your firmware Christian it works perfectly.
One thing you forgot to mention is that you have a inverted z-motor so i had to change that too
But apart from that everything is working very smooth now.
Thank you for your help.
Regards,
Erik[/quote]
Yep, sorry, i forgot to mention that i use a hanging z axis …
Happy printing!
cheers,
Christian
