I’ve been working on a project in which readings from 2 different sensors are displayed on a 7" TFT screen. Readings from 1 sensor are used to determine the value to write to a servo. The servo then moves a small panel which is then used to obtain a distance reading from the second sensor. The servo is rated for use from 4.8-6V. In the image I have attached, the alligator clips are attached to an external variable DC power supply. The Servo is connected to the supply with a 470 nF Capacitor between the servo and the power supply. The Arduino is also powered by the supply through the Vin pin.
I have been having an issue with the Arduino turning on and off when I use the external supply to power everything unless it is set to 6.5V or greater. I could be wrong, but I think that the Arduino voltage regulator should be able to handle this. I am worried about the servo. There is not a large load exerted on it, so I thought that I should be ok using near 5V to power, but currently that is not the case. I basically have 2 questions. Can I power everything with 6.5V without damaging the servo? If not, is there another way to work around this? Ideally, I would like the system to be powered by 1 supply via a wall outlet.
I accidentally cropped the image instead of resizing it. Sorry about that
The Servo is connected to the supply with a 470 nF Capacitor between the servo and the power supply.
You should use a 470 uF (microFarad) or larger capacitor in parallel with the servo power leads, if used at all.
The power supply should be capable of handling the servo stall current, which is typically 1 Ampere, but can be as high as 3 A for powerful servos.
The Arduino Uno is specified for 7 V minimum on the barrel jack or RAW input. Best to power it separately when motors or solenoids are involved. Don't forget to connect all the grounds.
For more informed help, post links to the power supply, your servos, and post a schematic diagram.
Thanks for the quick response! I have attached the links to components being used.
I have also attached a circuit diagram of the power supply, Arduino, and Servo. I forgot to label the capacitor, but it is a 470 nF capacitor. If it will help solve my problem, I will switch it out with something larger.
When I set the power supply to 6.5V, the max current draw (according to the screen on the supply) is around 300 mA. Also, in my setup, the servo should never be operating anywhere near the stall torque as there will never be any significant external forces exerted on it.
the servo should never be operating anywhere near the stall torque as there will never be any significant external forces exerted on it.
But it still draws 1.8Amp (stall current) for a short time when starting to move from standing still.
470n is 1000 times less than 470uF.
Would a supply with a large enough amperage usually solve the problem then? I also have a 5V 3A power supply that I was testing with and I had the same issue. Also, is there an optimal capacitor to use? I know that jremington said to use 470 uF or larger and understand the difference between micro and nano. I was just stating what I was currently using in the circuit. Is there a maximum value that I should try to stay under for the capacitor? The kit that I have doesn't come with a 470 uF
Well, if... the stall current spike of the servo is causing the trouble, then you have to fix that.
The 5volt regulator on the Uno needs a minimum of ~6.5volt on V-in to do it's job.
And the servo is out of specs (and draws more current) above 6volt.
Stuck between a rock...
Two seperate supplies might be needed (with common ground).
Try powering the Uno with a cellphone charger, connected to the USB socket.
And the servo with that lab supply, set to 5volt.
470 nF capacitor. If it will help solve my problem
That capacitor is doing nothing useful. The servo power supply is the problem. If you have it set for a low constant current as overload protection, change that to the maximum possible.
You could set the lab power supply to 6V and use an efficient, low dropout voltage 5V stepdown converter to power the Arduino through Vcc. This one should do.
It sounds like I might have to use 2 power supplies. Everything works when I power via the USB. Would I be able to use one 6.5V power supply and connect to the servo through the Step Down Converter that I linked below?
Just out of curiosity, will running the servo at 6.5V damage it or any other components, or is it possible to get away with it?
You need 7 V minimum to power the Arduino through the RAW or barrel jack.
Obey the manufacturer’s recommendations for long servo lifetime.
Ok got it. So then a 7V DC power supply and a step down voltage regulator between the supply and the servo should solve my problems. Correct?
Yes, as long as the 7 V DC power supply AND the regulator can easily supply the servo stall current.
Would a supply with a large enough amperage usually solve the problem then? I also have a 5V 3A power supply that I was testing with and I had the same issue.
If I've understood what you're doing a 5V 3A power supply would be ideal for that set up.
But you MUST connect it to the Arduino 5V pin not to Vin or the barrel connector (assuming it is a 5V Arduino of some sort that you're using).