Wiring effector

I am building a metal kossel mini, and I'm about to wire the effector. I would like to create a connector between everything in the effector and the wires going to my controller (a Arduino Due with RADDS), so I can easily disconnect it.
The question is: how many wires do I need, or more specifically: how many 'grounds' can I join?

I have:
-heater: 2 wires
-thermistor: 2 wires
-hotend fan: 2 wires
-cooling fans: 2 wires
-DC42 ir probe... 3 wires?

If I didn't join any grounds I would have 11 wires, but I assume that the at least the fans have common ground..(?) and the heater, can I use the same ground? and the thermister? It's a variable resistor right? Is that wired between two pins, or between ground and 1 pin? And anyone know about the DC42 ir probe? I assumed it has ground, 5V and an output? So I could join the 5V with the 5V of the hotend fan (always on), and the ground with other ground? Then I would get:

-ground 1 wire
-heater: 1 wire (+ ground)
-thermister: 1 wire (+ ground)
-hotend fan: 1 wire (+ ground)
-cooling fan: 1 wire (+ ground)
-Dc42 ir probe: 1 wire (+ground + 5v from hotend fan)

Then I would need only 6 wires. But I'm really unsure if I can do this. I can measure ofcourse if the grounds are connected, but I guess I'm not the first one who is trying to minimize wires so I thought I should ask first before experimenting and killing my arduino , and maybe there are other considerations that I don't know about.


Second question; I remember Tom (Sanladerer) mentioning that ethernet cable can be good option, which has 8 wires, and I have a lot of that.I think he even said something about that it could handle the amps from the heater. Mine is 40 watts for 12 volt I think, so that's about 3+ amp. Any thoughts on that?

Edited 1 time(s). Last edit at 09/23/2016 06:46PM by BramV.

I recommend you don't share any grounds on the IR sensor and the thermistor, to avoid ground noise and to avoid feeding 12V or 24V into the sensor or thermistor circuit if a ground wire breaks. At a push you could share the IR sensor and thermistor grounds.

The two fans and the hot end heater probably have the positive sides connected to +12 or +24V so you can share that wire. Therefore you need 3 wires for the IR sensor, 2 for the thermistor, and 4 for one heater and 2 fans. Total 9.

I've been thinking about manufacturing a small board that fits on the hot end to control the hot end temperatures and fans and to pass measurements back to the main electronics. My provisional design uses 2 power wires and 3 signal wires, and it would control up to 4 hot end heaters with no increase in the number of wires needed.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

So basically you suggest sharing the ground between hot-end fan, filament-fan and heater? Shame it's not 8 wires instead of 9, but I'll go for a 10-pin connector then.

The board you describe seems like a good idea. "The number of wires to the hot-end is too damn high!" 3 signal wires, how are they used? How about 1 wire I2C?

Quote
BramV
So basically you suggest sharing the ground between hot-end fan, filament-fan and heater? Shame it's not 8 wires instead of 9, but I'll go for a 10-pin connector then.

It's actually the +12V or +24V wires that can be shared, but same idea.

Quote
BramV
The board you describe seems like a good idea. "The number of wires to the hot-end is too damn high!" 3 signal wires, how are they used? How about 1 wire I2C?

It's not a good idea to mix power and signal grounds, especially when the heater is running with PWM. That rules out I2C and one-wire - also both of those are very susceptible to noise because of the passive signal pullup. Async serial with opto isolators is what I had in mind, and that can be done using 3 wires. I guess RS422 is another possibility, and I'm open to other suggestions.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I always assumed that the PWM for the heater and the fans are applied by turning voltages on and off on the +12 wires. So that's not the case? How exactly does it work?

I'm afraid I do not know enough about electronics to have other suggestions. However, when you mention opto isolators, does that mean you could not use your board design on current controller boards like duet or ramps?

All 3D printer electronics that I know of switch heaters and fans by connecting the positive power input directly to one side of the heater or fan and using a mosfet to ground the other side.

The opto isolators would be on the hot end board and would work with standard main board electronics.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Okay, that is good to know, thanks!

If you release this new hot-end board design, do you plan to make an update for the reprap firmware for RADDS as well? I seems like nobody is actively working on that fork anymore (says: terminated, [github.com]). The reason I got a due+RADDS instead of a duet is because I wanted to use the silent stepstick drivers (which work great by the way), and with the duet it didn't seem like I could replace the stepper drivers.

The GitHub repo for more recent versions of RepRapFirmware on RADDS is [github.com].

On the Duet WiFi we use TMC2660 drivers, which support up to 256x microstepping and are amazingly quiet. The older Duets only do x16 unless you wire alternative stepper drivers to the expansion connector.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
Async serial with opto isolators is what I had in mind, and that can be done using 3 wires. I guess RS422 is another possibility, and I'm open to other suggestions.

CAN?

Quote
dc42
All 3D printer electronics that I know of switch heaters and fans by connecting the positive power input directly to one side of the heater or fan and using a mosfet to ground the other side.

Probably because of low resistance MOSFETS with N channel are more common/cheaper. That would be my guess

Quote
hercek
Probably because of low resistance MOSFETS with N channel are more common/cheaper. That would be my guess

Could be from my intuition it would make more sense to have common ground and switch the positive voltages. But now I think of it, I don't know any specific reason why it should be that way, so I guess the cheapest option won?

Edited 1 time(s). Last edit at 09/25/2016 04:53AM by BramV.

N-channel mosfets typically have an on resistance an order of magnitude lower than P-channel mosfets. They also have the advantage that the drain, which is the main body of the semiconductor, is at 0v when used as a low side switch so you don't need to electrically insulate the heatsink from the mosfet (normally)

Moriquendi