Actions
Forum Thread Details
  • State Verified Answer
  • Replies 10 replies
  • Answers 2 answers
  • Subscribers 392 subscribers
  • Views 1292 views
  • Users 0 members are here
Related

Powering external devices with Arduino

balearicdynamics

Hi to all,

 

I'd like to discuss a question. I am working on the design of an Arduino shield that should manage a separate power to drive a couple of servos and another device driver by 3.3VCC from the Arduino board. What is your opinion about the better solution:

  1. Use a relais driven by an Arduino pin through a transistor, powered by the Arduino 5VCC to manage the two servo power, and power the 3.3 device with the same relais (has independent ports controlled simultaneously
  2. Use a four digital switches NTE4066BT (two pins only) while the other two are already used by the circuit
  3. Some better idea ?

My vision is that with a single relais (so using a single digital pin on Arduino) I can control the powering of the external components - that are controlled by the shield - These need to be powered together anyway when the program is started.

 

What do you think about ? Thanks in advance.

 

Enrico

Parents Reply Children
  • 0 in reply to johnbeetem

    None at all. Exclude the transistor.

     

    First because the servos drain almost considerable current, second because I have already experienced the transistors and they are not reliable.

     

    But what I ask is: why I should complicate the things - that are something like replacing a power switch with a relais - with a SSR + USN2003 ??? For about 3$ there are nice sub-micro relais that drive up to 2A from 5 up to 12 VCC... With one single component.

  • 0 in reply to balearicdynamics

    I wasn't suggesting both SSR and ULN2003 -- either use one or the other, depending on what you're doing.  My understanding is that your ultimate goal is to turn motors on and off, in which case the ULN2003 is a nice, cheap way to do it if you can use a common ground.  If you're just turning a separate board's power on or off, an SSR is nice.  If it's a lot of current, a mechanical switch normally has lower resistance but don't exceed the contact rating.

     

    Transistors are usually reliable.  However, you do have to make sure you don't exceed their voltage or current limits.  For example, if you're driving an inductive load like a motor, relay, or speaker coil you must use a flyback diode: http://en.wikipedia.org/wiki/Flyback_diode

    Otherwise when you switch the current off, the inductor will generate a high voltage spike that kills your transistor.  The ULN2003 has built-in flyback diodes.

  • 0 in reply to johnbeetem

    Hey John,

     

    thank you for your clarification. In fact I thought you want to use both image

     

    What you write is correct, I have already used ULN2003 to drive motors and as they have a limitation of about 1A, when I needed more power I have used ULN2004. In this case I have to manage with a separate power line low consuming devices (a micro camera consuming 180 mA) that need a separate power line for question of stability and a couple of micro servos. This is the reason that - in the need to automate all the manual commands (power, setting etc.) I though to use a micro-relay powering this part using the same 9Vcc battery-group (or wall-mount power) used to power Arduino but with a separate 5Vcc regulator. To drive the micro relais instead, I am using a N2222 NPN transistor. Maybe redundant or not, but there is the correct protection and no overheating in any place.

    I have tried before making the circuit and the things seems working, leaving some hours under test. A protection diode (4001) has been put anyway between the power connectors of the microswitch.

     

    Best, Enrico.