I’m somewhat new to the whole microcontroller-electronics area and as a first project I decided to work on a line following robot and I’m facing some difficulties on deciding how many regulators will I use and if it’s necessary to use one or two. The parts that I’m definately going to use are the following:
- Arduino UNO with a proto shiled on top with a mini breadboard attached
- QTR-8RC IR sensors using all 8 of them
- An ultrasonic sensor for obstacle detection
- TB6612FNG Dual Motor Driver
- 2 HP Micro Gearmotor 900RPM
- A 7,4 2S LiPo battery
- 9V Step-Up Voltage Regulator U3V70F9
- A 12V DC rocker switch to power on and off the robot
- S7V7F5 5V regulator (not sure about that)
My question is the following. Is it possible-advisable to use only the 9V step up regulator to power the arduino UNO through the Vin pin using the onboard 5V regulator as well as the motor driver? So I will be having two outputs from the same regulator. This particular regulator has built-in reverse voltage protection so I think that there is no danger of back EMF and the motor driver has capacitor filters so there wouldn’t be a noise problem with the system. Or it would be better if solder two wires at the accessories prong of the switch one to power the 9V regulator and the other to power the S7V7F5 5V regulator? Then, I would power the motors from the 9V regulator and the arduino UNO from the 5V regulator through the 5V pin. I know that it’s not advisable to power the arduino UNO through the 5V pin, because it bypasses the onboard regulator but I would be using and external 5V regulator adding reverse voltage protection too using a P type MOSFET transistor so I don’t image that it would be a problem. I’m a bit confused about which approach to take and what are the benefits of the one over the other.
Thanks a lot in advance.
It sounds like you are confused about the reverse voltage protection feature on the regulators you mentioned. The reverse voltage protection prevents damage to the board and devices connected to the output of the regulator in the event power is accidentally connected backwards (e.g. the GND pin to positive and the VIN pin to ground).
In your comment on my line follower blog post, it sounds like you are mostly concerned about noise from the motors being disruptive to the rest of the system. It is possible for motors to introduce problematic noise into a system, but I would not expect powering the Arduino Uno and motor driver from the same regulator to cause problems like that. However, if you are concerned about motor noise, you might consider taking some of the preventative measures discussed in this “Dealing with Motor Noise” app note.
You also mention that powering the Arduino directly from your 2S LiPo might not be a good option since it is only 0.4V above the recommended 7V minimum operating voltage. Please note that 7.4V is the nominal voltage for a 2S LiPo, and when fully charged, the battery voltage will be around 8.4V, so that should give you a comfortable margin.
As it seems I was indeed confused about reverse voltage protection. I was confusing it with the spikes occurred by the electromagnetic field created by the motors.
You are absolutely right about the LiPo battery. I was only thinking about the nominal value of the voltage, not the voltage when the battery is fully charged.
Nevertheless, using a regulator to have constant voltage across the motors while the battery drains out, is essential in order to have somewhat of a predictable behavior, so I’m definitely going to use one. So there’s no problem powering both the microcontroller and the motor driver from the same regulator, provided that any noise that might occur will be filtered?
A regulated motor voltage is certainly helpful for getting consistency when making a line follower. As I mentioned before, I do not expect any problems from powering both your Arduino and motor driver from the 9V regulator, provided it can handle the current draw of them. We have made many line following robots for our local competitions using this configuration (even without additional capacitors to filter possible noise), but if you are concerned about it, filtering out the noise with capacitors is a fairly simple precaution to take.
The output of the U3V70F9 regulator that I’m planning on using can provide 7A of current for prolonged durations and the whole system will need 4A at the most, so there’s no problem with that…Thank you very much for your help.