Red (power: pin 2) wire for servo motor not connected

[adamaero]

Why is the red (power: pin 2) wire for the servo motor not connected to anything in this circuit?
https://github.com/samyk/combobreaker/blob/master/Eagle Files/ComboBreaker_top.pngAlso, on the "bottom" schematic, the ground is connected to the feedback (potentiometer wiper) line:
https://github.com/samyk/combobreaker/blob/master/Eagle Files/ComboBreaker_bottom.png
Since I am making this project without the encoder, should I still connect that feedback line to the ground?


Sorry, there are two different questions. If I had to make an educated guess, I would connect:

• red wire of the servo (pin 2 of 4) to the stepper driver (pin 7)--even though that is labeled as ground in the datasheet (see how that is also connected to the +5V of the Arduino)
• yellow wire (pin 3 of 4) to the digital input of the Arduino (pin D9)
• brown wire (pin 1 of 4) of the Servo's pin 1 to the analog input of the Arduino (pin A0).

Sources
https://www.arduino.cc/en/Reference/Servo

The power wire is typically red, and should be connected to the 5V pin on the Arduino board. The ground wire is typically brown and should be connected to a ground pin on the Arduino board. The signal pin is typically yellow, orange or white and should be connected to a digital pin.​

 

[CWatters]

red wire of the servo (pin 2 of 4) to the stepper driver (pin 7)--even though that is labeled as ground in the datasheet

Which data sheet?

Why is the red (power: pin 2) wire for the servo motor not connected to anything in this circuit?

Perhaps I misunderstand but.. Pin 2 of the "Servo" connector _is_ connected to something. It's connected to the power plane on the top layer. See arrow.

 

[CWatters]

Generally power (5V) and ground (0V) are needed everywhere on a PCB because all chips need power. Instead of using PCB tracks for power (5V and 0V) what they usually do on a 2 layer (eg double sided) PCB is flood all unused space with copper and use that like a big track. On one side that's used as power and on the other it's ground. Clearly signal tracks could cut these planes into isolated smaller planes, in which case wire links have to be added to ensure they are all connected together.

On a 4 layer PCB things are easier as the inner two layers can be reserved for Power and Ground only and the outer two layers used for other signals. This gives you a nice large plane of copper on the inner layers to distribute power and ground. Connections are made to the inner layers by drilling a hole and electroplating the inside of the hole.

On the image below I've tried to highlight all the connections to the Ground/0V plane. I can't guarantee I haven't missed one but I think I got them all.

 

[adamaero]

Ok, thank you. I did not realize those notches in certain parts physically meant ground. Although, I am still confused. Should I disregard the wiring order of how the servo is manufactured? It is brown (ground), red (power), yellow (signal). Wouldn't that ground pin 2, red wire? Why?

Thank you for taking the time CWatters.

 

[CWatters]

STOP PRESS...

I've been looking at the layout more carefully and it appears they might be using both sides for 0V (eg the top plane isn't 5V it's 0V as well). More to follow...

 

[CWatters]

Ok yes my mistake, both of the planes appear to be 0V on this board and pin 2 on the servo is connected to 0V. See numbered comments on the diagram..

 

[CWatters]

Ok, thank you. I did not realize those notches in certain parts physically meant ground. Although, I am still confused. Should I disregard the wiring order of how the servo is manufactured? It is brown (ground), red (power), yellow (signal). Wouldn't that ground pin 2, red wire? Why?

Yes you will need to figure out which of the 4 pins on the PCB the 3 wires of the servo should be connected to.

It looks like Pin 2 = 0V = Brown wire but the others are harder to work out. Is there a circuit diagram for the PCB? I couldn't immediately see one.

Note that the project uses a different servo to the one you posted. It uses this one that has 4 wires, the extra wire provides feedback on the load on the servo. So it can tell when the padlock is open.

https://www.adafruit.com/product/1404

 

[CWatters]

Just for info..

I think the pins used on the PCB will be fatter than the connector provided on the servo. The spacing might be different as well. So you may find you have to replace the connector anyway or solder wires direct to the PCB. Check before you remove the connector.

 

[adamaero]

Yes you will need to figure out which of the 4 pins on the PCB the 3 wires of the servo should be connected to.

It looks like Pin 2 = 0V = Brown wire but the others are harder to work out. Is there a circuit diagram for the PCB? I couldn't immediately see one.

Note that the project uses a different servo to the one you posted. It uses this one that has 4 wires, the extra wire provides feedback on the load on the servo. So it can tell when the padlock is open.

https://www.adafruit.com/product/1404

No, unfortunately there is no circuit diagram.
Yes, I am using that servo (with the white wire). Although, I am not using the encoder. Will the servo need to be taken out completely?
I will disregard the order the servo motor is made in respect to the PCB layout.

 

[adamaero]

Just for info..

I think the pins used on the PCB will be fatter than the connector provided on the servo. The spacing might be different as well. So you may find you have to replace the connector anyway or solder wires direct to the PCB. Check before you remove the connector.

I'm just connecting everything with wires. (I'm not making the PCB.)

 

[adamaero]

Even though this goes against how the wire order the servo was manufactured in, I'm just doing to connect them in this order, fire it up, and see what happens...

• yellow wire (pin 3 of 4) to the digital input of the Arduino (pin D9)
• brown wire (pin 1 of 4) of the Servo's pin 1 to common ground
• red wire (pin 2 of 4) the analog input of the Arduino (pin A0)
• white wire, even though it doesn't do anything, to stepper driver (see Eagle File)

 

[CWatters]

The servo will almost certainly be designed for...

Brown - Ground 0V
Red - power 5V
Yellow - signal (typically a pulse between 1 and 2mS long repeated 50Hz)
White - Analogue feedback

 

[CWatters]

So I would connect

The red wire would normally just be connected to 5V but on some circuits you want to be able to turn off power to the servo.
The brown wire to 0V.
The yellow wire to a digital output on the Arduino.
The white wire to an analogue input on the Arduino (if the servo has one).

 

[adamaero]

So I would connect

The red wire would normally just be connected to 5V but on some circuits you want to be able to turn off power to the servo.
The brown wire to 0V.
The yellow wire to a digital output on the Arduino.
The white wire to an analogue input on the Arduino (if the servo has one).

I am not using the encoder component; the white wire will not do anything.

I found the schematic though... just trying to open the .sch file...

 

[Tom.G]

just trying to open the .sch file...

Both ORCAD and PSPICE use the .SCH file extension.

 

[adamaero]

I did not realize Eagle was free.
http://imgur.com/a/MmLqF