I'm not sure what capacitor I should use

Other Hardware General Electronics
1

I'm currently doing a project where I have my arduino uno powering the LCD screen that came with it and am looking to power a servo using the arduino's 5Vout as well. However, the servo seems to be drawing too much power and the display on my LCD flickers/disappears. I read in another forum that a capacitor could help, but I don't know what kind I should use. I also don't want to use an external power supply if I can help it as I'm already using a 12V external supply for a solenoid I'm using as well. Any help or suggestions would be great, Thanks.

Servo:
DFRobot DF15RSMG 360 Degree Motor (20kg)
Rotation angle range: 360°
No-load speed:60°/0.16s @7.4v
Stall torque:19.3kg.cm（7.4v）
Dynamic torque:15.1kg.cm（7.4v）
Gear:steel,copper mixed gear
Assembly method:fastening with double layer 4 screws Equip 2 pairs of shells,2 metal servo horns and 2 servo support
Size: 40x40x20 (mm)

Electrical specification

Working Voltage: 5-7.4v
Stall current:3A(@8.5V - Limit test)
PPM Voltage:3V-5V
PPM Resolution:2us
PWM driver frequency:4KHZ
Range of PPM positive pulse width:400us-2550us
Minimum value of PPM negative pulse width:400us

(http://www.amazon.com/gp/product/B014L5CBBA?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s01)

2

You could try a beefy electrolytic cap - but it's really best to give it it's own 5v supply. You don't want inductive loads on the same supply as the microcontroller. Maybe you could use one of these cheap buck converters dc-dc step down for sale | eBay to get 5v for the servo from that 12v supply? That's probably what I'd do.

3

What external PSU are you using?

Arduino can provide only as little as 0.4amps which is not enough for a servo alone.

You MUST use an external power supply for the servo/servos and another one (or the same one if it does provide enought amps) for the Arduino (usb amps is very low, usually not enought for an LCD).

In short, use an external PSU, it's pretty much MANDATORY.

4

A capacitor will not compensate for an inadequate power supply. What is the current capacity of your supply.

5

Servos can easily take bursts of over 1A, you do not power them from a logic supply
rail if you want a working project!

6

Did you try with external PSU?

7

MarkT:
Servos can easily take bursts of over 1A, you do not power them from a logic supply
rail if you want a working project!

Your spec gives the stall current as 3 A. That is more or less the current it will draw momentarily when starting from standstill. Much too high for the Arduino.

Russell.

8

DrAzzy:
You could try a beefy electrolytic cap - but it's really best to give it it's own 5v supply. You don't want inductive loads on the same supply as the microcontroller. Maybe you could use one of these cheap buck converters dc-dc step down for sale | eBay to get 5v for the servo from that 12v supply? That's probably what I'd do.

Sorry, obviously I don't know much about electronics, but this seems like a good idea. I don't know how to program/adjust these but it seems like I could buy ones that step down from 12V to either 5 or 6V. So that leads me to me next question, which would be better for this servo (5 or 6V step down) and also, these step downs say they 3A as well, will that be a problem with the stall current being 3A?

Thanks for the help, I really appreciate it.

9

These step downs would just trigger the over current protection they contain if faced with an overload and then start up again so it should be fine.

A servo is happier working at 6V like it was designed to do. It will also move faster.

10

DrAzzy:
You could try a beefy electrolytic cap - but it's really best to give it it's own 5v supply. You don't want inductive loads on the same supply as the microcontroller. Maybe you could use one of these cheap buck converters dc-dc step down for sale | eBay to get 5v for the servo from that 12v supply? That's probably what I'd do.

Also, do you think I could use an additional step down from 12v to 9V, 3A to power the arduino? that way everything is powered off of one power supply? If so, I'd imagine it'd be important to not that i'd be using the 12v supply to power a 12v solenoid, the servo, and the arduino, if that makes it less likely to work. (if I can and it just means i'd blow through batteries a lot because it'd drain them so fast, thats not that big of a deal)

11

I would use one to drop the 12V to 5V and feed that into the Arduino directly bypassing the linear regulator. That would be way more efficient and give you longer battery life.

12

Grumpy_Mike:
I would use one to drop the 12V to 5V and feed that into the Arduino directly bypassing the linear regulator. That would be way more efficient and give you longer battery life.

How exactly would I go about doing that? I'm pretty new to arduino, I've only taken one class with it so I don't know all too much yet.

13

Grumpy_Mike:
I would use one to drop the 12V to 5V and feed that into the Arduino directly bypassing the linear regulator. That would be way more efficient and give you longer battery life.

I guess what I should be asking is, which way should I use to feed that into the arduino? The 5V pin, Vin pin, or the DC power jack? And if I use the 5V pin, can I just plug that into a bread board to power other things like an LCD screen and then wire the positive track to the arduino to have it work?

14

How exactly would I go about doing that?

Use another DC / DC converter wired to the 12V.

And if I use the 5V pin, can I just plug that into a bread board to power other things like an LCD screen and then wire the positive track to the arduino to have it work?

Yes use the 5V into power the whole shooting match apart from the servo.