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I have a project for automatic submersible pump actuation using a microcontroller.

I've done for two voltages like 5 V and 12 V and its corresponding relay. Also, in each board there is a transistor circuit for the motor actuation. It's nothing special. At any given time, the pump is getting actuated either by transistor circuit or by relay circuit, but not both at the same time.

Some points to be noted are:

  1. I'm driving the 5 V circuit using a 5 V, 5 A, DC adapter and the 12 V using a 12 V, 5 A, adapter.
  2. Motor current is around 250 mA. Is this circuit OK for the inrush current of the motor? I'd given the max value of i/p caps - is that OK?
  3. Is a reverse protection diode necessary at the power input side here? I'm powering the board using a DC jack and if I use a diode then there's a diode drop I've got to allow for in ADC calculations.
  4. I'm not using external reference voltage so I haven't connected the VREF.
  5. PCB snapshot is also attached. Let me know if you need any information from my side.
  6. Please check the overall circuit and let me know in case if I've to change something.

12V Schematic

5V schematic

12V PCB

5V PCB

adamaero
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Anil Suha
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2 Answers2

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2. Motor current is around 250 mA. Is this circuit OK for the inrush current of the motor? I'd given the max value of i/p caps - is that OK?

Diodes should take care of that. I don't know what i/p caps means.

3. Is a reverse protection diode necessary at the power input side here? I'm powering the board using a DC jack and if I use a diode then there's a diode drop I've got to allow for in ADC calculations.

During normal operation, the diode drops its typical ~0.6 V. That could be a significant portion of the supply voltage, and as the battery voltage decreases the device may stop working prematurely. Any component that has a voltage drop across it and current flowing through it is consuming power. If that dissipated energy comes from a battery, the diode is reducing battery life. This may not be an acceptable trade-off in devices that have very low risk of experiencing reverse polarity.

https://www.allaboutcircuits.com/technical-articles/how-to-protect-your-circuits-using-only-a-diode

So is there a low risk of reverse polarity? I would follow the recommendations of the part datasheets and whatever guide you're modeling after.

6. Overall circuit

It's hard to say. Again, I would have to analyze each datasheet for each part... which I suppose I can do:

enter image description here

Oscillator looks good. I'm not sure how the other capacitors attached to the microcontroller fit in.

  • Ultrasonic sensor pinout and bypass cap looks good.
  • Other smaller circuits look functional.

Related

adamaero
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I will move LED1 from that position and I'll connect it on pin 2 of relay...

In your configuration LED1 marks only that you have given a signal to relay, suppose relay or something after the relay is faulty... you see your LED on and this is not much information...

If you move the LED on pin 2 of the relay, your LED indicate that current is flowing from relay, so it gives you much more informations: that the relay have switched, and that the current is flowing trough the circuit.

Connecting LED1 across pin2 of relay and collector of the transistor will gives you a double check because now you know that relay is working and even the transistor is working.

gino
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