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Connecting a second servo to BS1 project board — Parallax Forums

Connecting a second servo to BS1 project board

dmehlingdmehling Posts: 25
edited 2008-07-09 00:02 in BASIC Stamp
Awhile back I began playing with a BS1 project board and built a voltage regulator on the breadboard part in order to operate a servo. My project goal has now expanded, and now I want to use an additional servo. Both servos will not be operating simultaneously so I don't think I should have any problems with powering the two of them. I need to know what exactly should be done to make this happen. Do I need to have a second voltage regulator, or can I use the same one for both servos? For reference please see this previous discussion thread which shows exactly how my original set up was constructed:
http://forums.parallax.com/forums/default.aspx?f=5&m=215628

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2008-07-03 18:31
    It's not clear from your post or from the thread you referenced just what your setup is.

    If you have a pretty standard voltage regulator that can supply on the order of 1A and is powered from Vin or some other suitable source, and the one servo seems to work ok, then you should be able to add a 2nd servo to the same regulated supply, An idle servo doesn't draw much current. Peak current for a single servo is about 1A. Average current is maybe 250mA when the servo is moving under low load.
  • dmehlingdmehling Posts: 25
    edited 2008-07-03 19:57
    Okay, I have built a 5v voltage regulator on the breadboard of my project board according to the instructions on this webpage: http://www.iguanalabs.com/7805kit.htm

    Also, take a look at this drawing someone made for me that gives an overview of this whole setup. Just ignore the car battery hookup since I am simply using a standard AC outlet. I need to now based on this current setup where or how I should add the other servo.
    BS1.jpg
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    BS1.jpg 22.1K
  • dmehlingdmehling Posts: 25
    edited 2008-07-06 18:27
    Anyone else have any suggestions? It sounds like it shouldn't be a problem to use the same voltage regulator to power my second servo as well as the first one. I just don't want to do anything stupid and destroy my project board since I'm still pretty new to this.
  • FranklinFranklin Posts: 4,747
    edited 2008-07-06 19:38
    The other servo uses the same power as the first and a different pin from the stamp for the signal.

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    - Stephen
  • dmehlingdmehling Posts: 25
    edited 2008-07-06 20:45
    Yes I am aware of that aspect.
  • DgswanerDgswaner Posts: 795
    edited 2008-07-07 01:19
    Dmehling, from what I remember you are using a LM7805 IC which is a 1A linear power supply, Rather than us giving you a fish, let's teach you how to fish, do some research on your Servo, you should easily be able to find the amperage, or miliAmperage (mA) of the servo. If you times that by 2 (2 servos) plus you'll need the Ma of the BS1 (it's on the parallax website) if your using the power supply to power the BS1. add them all together, if it exceeds 1000 mA ( 1A) your have a problem, if not your all good. it's a basic problem of supply and demand. You also need to keep Peek mA values in mind, if your the servos were 400 mA but 600 mA peak, you could brown out your processor if both servos peaked at the same time. there is ways to deal with that but let's keep it simple for now.

    I'm not trying to sound snotty or rude, or like a know it all, I'm just trying to help you along the road to bigger and better. been there done that!

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    "A complex design is the sign of an inferior designer." - Jamie Hyneman, Myth Buster

    DGSwaner
  • dmehlingdmehling Posts: 25
    edited 2008-07-07 16:51
    No you're not being rude at all. I'm just asking those who have done something like this before because it's hard to find good information on some of the finer details on this kind of project. I'm on a shoestring budget and I don't want to destroy anything. The two servos I am looking at using do not list a peak current value. They are rated at 180 mA no-load operating current which doesn't seem like a very helpful number. I'm not too worried though because the application for the servos is definitely not heavy duty, so I think they should not require much amperage. Also, both servos will not ever be operating simultaneously in this application. Finally, I'm not exactly sure how to connect the second servo. Can I connect the power and ground header pins of servo #1 to the power and ground header pins of servo #2?
  • DgswanerDgswaner Posts: 795
    edited 2008-07-07 19:07
    as far as operating mA it sounds like your good to go, 360 mA total for both servos, that's not even 1/2 the 1000 mA your power supply can provide.
    as far as connecting another servo, the Basic stamp 1 project board makes it really easy, all you need to do is soldier in another 3 pin connector to the board and your good to go, see this diagram for details http://forums.parallax.com/forums/attach.aspx?a=16827

    just FYI, the power can be connected directly from one servo to the next, positive to positive, negative to negative. the I/o connection needs to be separated, and only one i/o line can connect to one servo. this is all done for you on the project board.

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    "A complex design is the sign of an inferior designer." - Jamie Hyneman, Myth Buster

    DGSwaner
  • dmehlingdmehling Posts: 25
    edited 2008-07-07 19:17
    Thank you so much. I was thinking I could do it exactly as you have just explained, but I wasn't sure if it was recommended. I would really like to see that diagram, but none of the URLs for previous discussion threads seem to work. If you tell me who started the thread and the subject I might be able to find it.
  • dmehlingdmehling Posts: 25
    edited 2008-07-08 21:30
    I was talking to someone else today about this project, and they suggested that it is not a good idea to be regulating the voltage to the servo and that I should be using a switching regulator. I believe my adapter is supplying about 12 V, which means the voltage is reduced by more than half by the time it reaches the servo. Do you think this might be a problem? I'm not worried about energy waste, but I am worried about the possibility of too much heat.
  • ercoerco Posts: 20,259
    edited 2008-07-09 00:02
    A linear voltage regulator heats up just like a series resistor would. The more current flows, the more heat dissipated. The greater the voltage drop (Vin-Vout), the more heat dissipated. A switching regulator would be a cooler and more efficient solution, and actually I just posted a link to some simple switching regulator circuits in this column today. Very timely, yes?

    If you want to stick with linear regulators, here are a few suggestions:

    Servos can take more than 5 volts, so you could use an adjustable regulator like an LM317T to give them 7.5 or 8 volts for snappier action, plus, the regulator will run cooler than 5 volts (less drop). the LM317T is rated for 1.5 amps if you heat sink it.

    If both servos may be on at the same time, you could give each its own regulator to spread the heat over twice the hardware. Same total heat given off, but less localization.

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    ·"If you build it, they will come."
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