Please review my schematic/circuit diagram.🙏 Will this useless box circuit survive or will it fry something?

Projects General Guidance
1

Hey folks,

I'm building a personality-based useless box that reacts differently depending on the selected "mood" (Lazy, Adamant, Irritated). I'm using:

  • Arduino Uno
  • DFPlayer Mini for voice lines
  • 2 SG90 servos (lid + arm)
  • HC-SR04 ultrasonic sensor
  • SPDT toggle switch (to trigger the reaction)
  • Push button (to change the box's personality)
  • 3 LEDs for visual feedback
  • TP4056 (charging circuit)
  • MT3608 (boost converter for 5V output)
  • 2x 3.7V 2000mAh Li-ion cells in parallel
  • Some passive components (diodes, capacitors, resistors for servos and logic)

I’ve added 1N4007 diodes to prevent back current into the MT3608 and 1000µF capacitors near the servos to handle inrush. There's also a voltage divider (680Ω + 1kΩ) for DFPlayer RX, and 100µF caps near the DFPlayer’s VCC and GND.

Here's my schematic (KiCad).

schematic
schematic1250×687 15.5 KB

Questions:

  • Will this cause any power conflicts between Arduino + MT3608 + DFPlayer + Servos?
  • Are the diode/capacitor placements and values good enough?
  • Would this design cause brownouts or overheating?
  • Any recommended fuses/protections I should add?

Any tips/suggestions before I start soldering and boxing it up would be amazing!

Also please bare with the wires being so messy. This was my first time using a schematic making software, in fact, this is my first time making something with so many parts and wires.

Thanks in advance :folded_hands:

2

Also, I am open to any suggestions to improve it and stuff.

3

Never put batteries in parallel. It dangerous, can lead to leakage and /or explosion.

4

I was thinking the same thing actually. But ChatGPT insisted to put it in parallel. Can you suggest what to do instead?

5

Just use one battery!

6

Will do. Any other suggestions or improvements ?

7

Why do you have diodes on the servos?
How much current do these servos need?
Why do you have a100uf cap across the speaker?
The voltage divider is backwards.

In general it's not a good idea to power an Uno via the 5V output pin.

I think the only correct thing are the 3 LEDs,

1 Like
8

A little hard to read, but do I see a battery going to a step UP converter then a step DOWN converter?
With all the losses, the battery might last a few minutes, assuming you have a source of genuine 18650 cells; it is probably the most faked item for sale on the net.

9

I'm pretty sure that the MT3608 does not have an auto-shut-off to protect the battery from over-discharging for when the battery gets low. So it's important that your TP4056 module does have that feature. Not all TP4056 modules have it. Can you post a link or photo?

10

I thought MT3608 is a step down converter.
EDIT: It's BOTH UP and DOWN. COOL.

12

My turn to say "I thought"!

I thought I read that if the input voltage is >5V, it by-passes the step-up and outputs that higher voltage.

Not a problem here.

13

@lazykillerking
It looks like you did everything Chat told you to do but 90% of it is totally wrong.

2 Likes
14

You have connected that incorrectly. It won't reduce the voltage like that.

15

So what is the purpose of the TP4056? It isn't charging anything.
With AI, electronics engineers and technicians are ensured full employment fixing all the smoking wrecks.

16

@lazykillerking
Have you bought any of the components yet?

17

All TP4056 modules I've seen (and I'm assuming it's a module and not a bare chip) have a USB input socket, as well as a voltage input. Presumably @lazykillerking will use the USB socket to charge the battery.

However, I don't know if the TP4056 will work correctly if power is being drawn from the battery at the same time it is being charged. So probably need a switch to turn off the circuit when charging.

18

Thanks for the feedback, Jim. I’ll walk through a few points you brought up and would love clarification if I still have gaps.

  • Diodes on Servos: These are reverse-biased 1N4007s between V+ and GND (not signal lines). I added them for basic flyback protection to guard against back-EMF when servos stop or reverse suddenly. If that’s unnecessary or poorly placed, happy to drop them.
  • Servo Current Draw: I’m using SG90-type micro servos. Based on online info and my multimeter, they draw ~250–300 mA under load, possibly up to 500 mA peak. Power is from an MT3608 boost module rated for 2A.
  • 100µF Cap Across Speaker: That was a misunderstanding on my part — already removed after your first note.
  • Voltage Divider: Appreciate you pointing that out. I’ll recheck it — I followed a DFPlayer youtube tutorial using 1k + 680Ω, but I may have reversed the high/low side. Would appreciate it if you could tell me how to do that.
  • Powering via 5V Pin: I’ve read about this concern. I’m feeding the Uno what i hope is 5.0V from MT3608. Bypassing the regulator isn’t ideal, so I’m considering switching to VIN to go through onboard regulation, though I was trying to minimize dropouts.

I have not bought TP4056 and MT3608 yet, I have the rest of the stuff.

I’m still learning and tinkering — that's why I am using ChatGPT’s suggestions. That said, I’m grateful you took time to go through the design.

Any more suggestions?

19

I harnessed mine from my dad's old laptop. so I am pretty sure they are not fake. they are 2000mAh 3.7V cells x6. I have yet to test if they are alright though. But the laptop's screen was broken pretty bad that's why we had to change the laptop so i think the cell's would be fine.

20

Here's the link to the modules. Do tell me if they would be good or not.

21

The diodes and big caps on the servos are not needed and actually those 1000uF may cause problems. You might put 100uF .

The top end of the divider should connect to the uno and the middle to the DFplayer.

Vin needs to be greater than 7V and less than 12V