Do you see anything wrong with this circuit?

Other Hardware General Electronics
1

Hello all,

My name is Andrea and I am relatively new to Arduino and electronics.
Also I am new to the forum, so forgive me if my question is not structured as it should.

I am trying to create a laser based game using few electrical components.
For the purpose of this circuit I am using the following components:

  • 2 X 5V Servo Motors

  • 1 X 5V Thumb JoyStick

  • 2 X 3V 532nm laser modules

Only one laser at the time will be on. Servos instead, are required to work together.

I was wondering if you find anything wrong with the schematic before my attempt in building it.
Also do you think that each servo needs a capacitor to smooth the signal?

schematic.png
schematic.png2574×1726 725 KB

Many thanks for your help and support in advance.

Best,

Andrea

schematic.png
schematic.png2574×1726 725 KB

2

OP image so we don't have to download it. How to post an image.

schematic.png
schematic.png2574×1726 725 KB

3

IRF520 MOSFETs are not logic level devices and will not turn on fully with 5V to the gate.

From the data sheet.
Drain-Source On-State Resistance RDS(on) VGS = 10V ID = 5.5 A Rds(on) 0.27
Plus note the high (for modern MOSFETs) on resistance.

Also do you think that each servo needs a capacitor to smooth the signal?

Not on the signal lines. Across the power supply might be appropriate to smooth the power during motor start surges.

4

andy-hgames:
I was wondering if you find anything wrong with the schematic

The main problem is that it's not a schematic. It's a Fritzing spaghetti diagram. A schematic would actually be readable.

One thing I do notice is the absence of resistors connected to the MOSFETs. One between pin and gate (to protect the pin); one between pin and GND (to keep the MOSFET off when the pin is set to input mode).

What's the use of the 12V power supply, other than stressing out the on-board regulator of your Nano? You have a 5V supply already. Can't imagine it doesn't have a few mA spare to power your Arduino as well.

5

Hello groundFungus,

Thanks a lot for your reply.
I have now properly attached the image.

What would you suggest using instead of the IRF520 MOSFETs ?

Would be ok to arrange the capacitors like in the image below?
If so, what value would be appropriate?

schematic 2.png
schematic 2.png2574×1726 442 KB

Best wishes,

Andrea

schematic 2.png
schematic 2.png2574×1726 442 KB

6

IRL520 would be the most direct alternative. Or IRLZ44N or IRLB8721PBF, just to name two others.

Check the datasheet. If there's no ON resistance given for VGS = 4.5V or lower, it's not a logic level one.

7

One more suggestion for the MOSFET.
FQP30N50L.
Logic level and very low on resistance (35 milliOhms at 5V gate).

Here is the MOSFET circuit with the resistors that wvmarle mentioned. Ignore the transistor part number. It is an old 5A device. Better the newer ones mentioned above.
MOSFET LASER DRIVER.jpg

MOSFET LASER DRIVER.jpg

8

wvmarle:
The main problem is that it's not a schematic. It's a Fritzing spaghetti diagram. A schematic would actually be readable.

Yes, I found it easier at the beginning to wire things up. Will definitely look into schematics.

wvmarle:
One thing I do notice is the absence of resistors connected to the MOSFETs. One between pin and gate (to protect the pin); one between pin and GND (to keep the MOSFET off when the pin is set to input mode).

I will add the resistors, thanks for the advice.

wvmarle:
What's the use of the 12V power supply, other than stressing out the on-board regulator of your Nano? You have a 5V supply already. Can't imagine it doesn't have a few mA spare to power your Arduino as well.

I will use the same power supply for another part of the circuit which deals with led targets and photoresistors; but yes will definitely have some spare current for the board. Thanks for the tip.

9

Remember 5V goes to the 5V or Vcc pin (markings vary between boards), not the Vin pin.

10

groundFungus:
One more suggestion for the MOSFET.
FQP30N50L.
Logic level and very low on resistance (35 milliOhms at 5V gate).

Here is the MOSFET circuit with the resistors that wvmarle mentioned. Ignore the transistor part number. It is an old 5A device. Better the newer ones mentioned above.
MOSFET LASER DRIVER.jpg

Thanks a lot for the clarification.
I will buy the correct MOSFET and add the resistors to both protect the pin and act as pull down.

11

wvmarle:
Remember 5V goes to the 5V or Vcc pin (markings vary between boards), not the Vin pin.

Thanks for the advice.

So I can connect my 5V 5A power supply directly to the 5V Arduino pin?
Does the voltage need to be regulated?

Also would this cause any issues if I upload a new sketch using the usb while the power supply is on?

Best wishes,

Andrea

12

I do assume that 5V supply is properly regulated of course...

And no problem with the USB uploads.

13

wvmarle:
I do assume that 5V supply is properly regulated of course...

And no problem with the USB uploads.

Thanks!

I am thinking of using a usb cable which goes from the 5V power supply to the actual usb female of the board.
This will reduce the risk of damaging the board.

I tested it already, I get 4.65V out of the 5V pin. I believe the board works well enough with this voltage.
Correct me if I am wrong.

Best wishes,

Andrea

14

It should work, but there may be another diode drop, not sure. You will lose some of the voltage you need to gate the mosfets, so it all depends on what you choose. There are logic level Mosfets that will trigger from 1-2.5V... suggest you search for something like that with the lowest Rds possible. Also the gate and pull downs are necessary, you can't have them floating. R2 can be even higher value to make it more efficient.

15

The 3V laser assemblies - are these bare laser diodes or complete modules with their own constant-current regulation?

Its best to post full information on every piece of hardware you reference, ie datasheets or product links, or we'll just have to keep asking you questions about it, such as:

What servos? What is their peak current demand?
What is the peak current demand of the last modules? What modules?

16

groundFungus:
One more suggestion for the MOSFET.
FQP30N50L.
Logic level and very low on resistance (35 milliOhms at 5V gate).

Here is the MOSFET circuit with the resistors that wvmarle mentioned. Ignore the transistor part number. It is an old 5A device. Better the newer ones mentioned above.
MOSFET LASER DRIVER.jpg

The mosfet suggestion and diagram are excellent. Just for the record, the IRL540 will work just as well.

17

MarkT:
The 3V laser assemblies - are these bare laser diodes or complete modules with their own constant-current regulation?

Its best to post full information on every piece of hardware you reference, ie datasheets or product links, or we'll just have to keep asking you questions about it, such as:

What servos? What is their peak current demand?
What is the peak current demand of the last modules? What modules?

Thanks for the suggestion.
Yes the lasers have their on module to regulate the current.

I will soon update the post with full specifications.

Best,

Andrea

18

HellasT:
The mosfet suggestion and diagram are excellent. Just for the record, the IRL540 will work just as well.

Thanks for the mosfet suggestion.

19

Thanks a lot everyone for your suggestions.

Here the new circuit design:

schematic.png
schematic.png2356×1708 675 KB

Components:

schematic.png
schematic.png2356×1708 675 KB

20

Please learn to draw a schematic diagram, and thereby avoid wasting everyone's time (especially your own) by using Fritzing.