Adding extra 5 volt pins?

No replies!  Yes you probably should give each device its own 5 volt supply using the 7805 rather than taking it from the 5v pin on the arduino.  It all comes down to current requirements.  

http://robotics.lib-ieronimoub.gr/?p=715

If your 9 volt supply can deliver enough current for the Arduino and all the devices than the 7805 can use that as its power supply to provide a 5volt rail for those devices.

If the device being controlled by the Arduino requires more than 5 volts power supply (like 12 volt motor) then you need another power supply for the device.

Pity there is a limit to how long you have to edit a post,  particularly if there are no follow up posts,  then you could fix any spelling mistakes and perhaps clarify the post.

I wrote: If the device being controlled by the Arduino requires more than 5 volts power supply (like 12 volt motor) then you need another power supply for the device.

This is incorrect, you could use a 12 volt power supply I was just thinking that it might be a good idea to have another battery because when  I  looked at the 7805 specs it said that although the supply voltage can be between 7 volt and 35 volt the difference between the input and output voltage is released as heat. The greater the difference between the input and output voltage, more the heat generated.

Hopefully someone with a bit more electronic knowledge will also respond to your post.

Shooting in the dark here (or at best early dawn), as I do not have details of the power requirements and layout for the individual components. However, I agree that you should not draw a lot of current from the Arduino (mega2560?). As @casey suggests the use of a single battery, that is regulated down to meet the voltage requirements is probably the best solution. As noted above the 78xx series of linear regulators are very inefficient (~50%) hence are not suitable for battery operated applications. There are, however, many DC to DC converters available on the market that have efficiencies in the range of 80% to 95%, that are inexpensive and easy to use. Below you’ll will find a link to one I’ve used recently. You can adjust the output voltage, and it will easily supply 1.5 amps.

I recommend a single battery simply from the point of view that it is a single battery to recharge. Only one battery to replace. If the application is sputtering, there is but one battery to check. However, it is not unheard of to see multiple batteries used in robots. It’s up to you. You’ll need to consider, space to mount the batteries, balancing and lowering the center of mass of the robot. Also wiring can tricky. If you employ connectors to attach your batteries to the robot, be sure to have different (or keyed) connectors. This will reduce the risk of plugging your 12 volt battery into your 5 volt Arduino.

One final suggestion: Work out your current (or power) requirements for each component and use this to select the appropriate cells/batteries. A single 9V battery can supply 500 mAh of charge. If your servos consume 2 amps, you will have an average of 15 minutes operating time. If you construct a 9 volt battery out of six AAA cells, that operating time goes up to three hours. Six AA cells will give you about 7 hours.

https://www.ebay.ca/itm/10Pcs-Mini-360-DC-DC-Converter-Step-Down-Adjustable-3V-5V-16V-Power-MP2307-Chip/221546307649?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

@dale

The boys are now looking at some thing like this set up.

Adding a second 9 volt battery then some thing like the above MP2307 then a ky-019 (1 channel dc 5 volt relay module) then a rail to attach the all the + and the - too. What they are hoping to do is when they power on the 2560 the 5 volt pin will turn on the relay module allowing 5 volts to run the 3 joysticks -6 -potentiometers and the nrf027l01( it has the adapter board to take the 5 volts to 3 volts).  They are trying to get away from having 10 + leads and 10 - leads all joined together and wired to the 2560.  The only other question they have is, do they join all the + leads and all the - leads together and have just one lead each going to the KY-019 or build a rail and run 10 individual wires.

@chickenhawk

I don't believe it matters. I can't imagine there is enough current flowing to justify a bus rail. I'd go for what ever looks better and is easier to maintain. Not necessarily in that order 🙂 

@dale

I think they are worried about running a jumper wire from one potentiometer to another potentiometer and so on. Don't know if there would be a voltage drop between the first and the last one to cause problems.  ( mainly by the time it got to the NRF24l01) So what do you think would be better running a jumper wire from one to the other or 1 main wire with leads running to each joystick and pots and nrf024l ?

@chickenhawk

Voltage drop is some times referred to IR drop. That is, current times resistance. If I assume that the wire lengths in question are less than five feet. The resistance of 10 feet of 26 AWG wire is around 0.4 ohms. I'll make another assumption that the power drawn by the pots and nRF are less than 20 mA. Ohms law gives us 8 mV of drop, which is less than 0.2%. Not really enough to worry about.

I've based my work on: Assumption #1

If you are also running the servos from the same power feed Assumption #2 , we are into somewhat of a different story. A single SG90 servo can draw as much as 100mA (more if it is under heavy load). Lets call it 6 servos, giving us 600mA all together. This amounts to 240 mV (~5%). Maybe not enough to slow the motors. but it maybe it could impact on the sensed voltage levels from the pots. I can say for sure.

I have made quite a few assumptions regarding placement of the components. If I am incorrect or have just laid a confusing mess out of the whole deal, please give me access to the implementation details (physical layout plans, electrical schematics, etc) and I'll try to do better. 

@dale

No all of this is inside the transmitter case. Longest wire  about 8 inches.   The ROV side is running 2 batteries.

This being a wireless system between the transmitter and the ROV. Are the boys maybe looking for problems that are not there?  The problem at the start was having 3 joysticks--6 potentiometers--1 NRF024l01 all drawing 5 volts from the 2560 overloading the system?  For right now they have not plugged everything in at one time, they have plugged one thing at a time to make sure the part worked. And now are ready to wire everything in all at once.

@chickenhawk

How much current can you draw out of the 5V pin on the mega2560? Nobody knows. However,  there seems to be consensus on a few facts. Powering the Arduino via the USB connector the board is not permitted to use and source more than 500 mA (not your situation).  The barrel jack feeds power to the processor chip via a regulator that is capable of one amp. The board itself uses about 200 mA. That works out to 800 mA free to be used else where. BUT NO!!! Don't try it. However, You should be able to draw 200mA without any problems. You can test this by powering up the board with a few different value resistors on the 5V pin. Monitor the voltage and look for a dip, when you attach the resistors. Four 100 ohm resistors in parallel should draw 200 mA. 

What is the resistive value of the pots? Do you have a spec sheet on the joy sticks?

@dale

The joysticks are 10k and the poteniometers are 10k as well.

From Spark fun:

This is a joystick very similar to the 'analog' joysticks on PS2 (PlayStation 2) controllers. Directional movements are simply two potentiometers - one for each axis. Pots are ~10k each. This joystick also has a select button that is actuated when the joystick is pressed down.

You should be just fine. max of 5 mA for the pots and joy sticks, and (if I remember correctly) 15 mA for the nRF.