2 power sources, 1 switch

Hi,

I’m making a robot that I plan to power with a power bank that deliver 5V throw 2 USB sockets (2A & 1.5A).

I’ll use the 1.5A output to power an Arduino & a camera and the 2A output to power the motors.

I will have one sliding switch to turn the whole robot ON/OFF. Here is my circuit (POWER, ANALOG IN, DIGITAL are Arduino IOs):

I have some questions about it (I’m not a electronic expert):

1. As you can see, I use the switch to cut the power from 5V BATT A, to cut the 5V BATT B I would like to use a MOFSET (MOTOR MOFSET in the Schema). I wire it like the one that control the camera but I would like to use the USB A output as signal. So when 5V BATT A is cut, 5V BATT B is cut too. Are R4, R5 necessary ? What must be their values ? What do you think ?

2. I want to measure my battery voltage. So I made a voltage divider with R1, R2. Since my battery is 5V (maybe 3.xV if I can link with the inside batteries of the power bank), do I need this voltage divider ?

3. Can you confirm I can plug directly my 5V battery to the 5V pin ? Will the 3.3V IO work ?

Thanks a lot for your help !

2 USB ports (2A & 1A).

USB ports have a maximum output current of 500mA, what do you mean here?

Since my battery is 5V (maybe 3.xV if I can link with the inside batteries of the power bank), do I need this voltage divider ?

You can not get 5V batteries what do you mean here? There is no need for a potential divider if that voltage does not exceed 5V.

That FET is an n-channel one and you seem to have the thing wired as a source follower, that is the load is in the source. That is not going to work very well if at all. You need a p-channel FET to do top switching.

Hi,

Thanks for this quick feedback :)

• I ordered this power bank: RAVPower 10400 mAh (doc), it have a 2A USB port & a 1.5A USB port.

• I want to watch the power bank power level but I see that this type of battery have a 3.xV cell, then tension is elevated to 5V so watching the 5V may not be very usefull, it would be better to watch the 3.xV. But anyway, thanks, I remove the potential divider.

• I have many RFP30N06LE MOFSET... Is there any other wiring that could make it work ? I would preferred not ordered new ones...

• Can you confirm I can use the 5V pin of the arduino to power it ?

pirquessa: I have many RFP30N06LE MOFSET... Is there any other wiring that could make it work ? I would preferred not ordered new ones...

An easy solution could be to wire it like the Camera MOFSET using a digital port of the arduino as a command ?

• I ordered this power bank: RAVPower 10400 mAh (doc), it have a 2A USB port & a 1.5A USB port.

I think your language skills ( and those of the writers of the web site ) are a bit lacking here. That is not a USB port it is a charger with a USB socket the two are totally different things and it is confusing when you use the words incorrectly. On the site there is a lot more context to compensate for the poor use of language.

I want to watch the power bank power level but I see that this type of battery have a 3.xV cell, then tension is elevated to 5V so watching the 5V may not be very usefull,

That is correct because there is electronics that boost the voltage and stabilise it so you see no change until just the end.

it would be better to watch the 3.xV

Yes it would but you would have to get at it first.

I have many RFP30N06LE MOFSET... Is there any other wiring that could make it work ?

You could wire it up as common source configuration. However when off that would leave the motor with +5V on both the power and ground inputs, and then any control signal would be below zero and so could damage your servo, so I would say no.

Can you confirm I can use the 5V pin of the arduino to power it ?

Power what?

An easy solution could be to wire it like the Camera MOFSET using a digital port of the arduino as a command ?

Again not sure what you mean.

Thanks for this detailed answer !

Sorry for my poor english, I'll try to be more specific.

Can you confirm I can use the 5V pin of the arduino to power it ?

Power what?

I would like to power the Arduino and the Camera with the same 5V output from the power bank. In the official doc I found:

5V.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.

.

Since I have a regulated 5V power source (with the power bank), I think I can supply voltage via the 5V pin to bypass the regulator and economize some watts. Two questions: Is the power bank a regulated power source (I think so) ? Will the 3.3V pin be powered (I suppose It's an other regulator that produce it, I don't know where) ?

An easy solution could be to wire it like the Camera MOFSET using a digital port of the arduino as a command ?

Again not sure what you mean.

I was looking for a solution with the RFP30N06LE MOFSET to emulate a switch on the second power line (5V BATT B).

Two questions: Is the power bank a regulated power source

Yes it should be.

Will the 3.3V pin be powered

Yes - but you can not draw very much current from this, typically 50mA max.

I was looking for a solution with the RFP30N06LE MOFSET to emulate a switch on the second power line (5V BATT B).

No you can not do that task with that FET for the reasons I have already told you about.

Ok thanks for the 3.3V :-)

Now I have to find a solution for this emulated switch... :(

The solution is to use a p-channel FET.