Shop OBEX P1 Docs P2 Docs Learn Events
power — Parallax Forums

power

JiggsJiggs Posts: 26
edited 2004-12-22 23:03 in General Discussion
Hi

My project requires several peripheral to interface with the Javelin, all of which require power. Connecting them all to the carrier board's power suply takes the system too much. I even made my own external power supply with a 5v voltage regulator and synced its ground with the Javelin's ground. This worked for awhile, but this too has failed. Does anyone have any ideas about how I can make a small but reliable power supply?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
~Jiggs

Comments

  • steve_bsteve_b Posts: 1,563
    edited 2004-12-21 15:50
    What failed on this second regulator circuit?

    How many peripherals are you connecting?· Check your regulator specs on what it's max current output is and then check the draw on all yer add-ons.

    If your add-ons' draw outweighs your regulators supply, then look at some of the bigger amperage regulators (2 or 3 A).

    I'm not sure you need to tie the grounds together on the two systems.....BUT, you would with the comm lines going between the units.· Not sure how you're reading their data.·

    Anyhow, I'd examine why it failed before putting another one on.·

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    ·

    Steve
    http://members.rogers.com/steve.brady
    http://www.geocities.com/paulsopenstage

    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
  • JiggsJiggs Posts: 26
    edited 2004-12-21 20:34
    The issue warrants more analysis. Sometime today I'm going to hook everything up to my scope and try and isolate the problem. Unfortunatley, the devices I have did not come with specs telling how much current they draw. But anyways, I have two Parallax servos, two SRF04 rangers, a Memsic accelerometer, and a serial transceiver.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    ~Jiggs
  • steve_bsteve_b Posts: 1,563
    edited 2004-12-21 21:02
    I couldn't certainly see right off the bat that you would be over your on-board regulators' abilities.

    What was the 2nd regulator cct you built?· the same regulator IC?



    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    ·

    Steve
    http://members.rogers.com/steve.brady
    http://www.geocities.com/paulsopenstage

    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
  • dandreaedandreae Posts: 1,375
    edited 2004-12-22 19:20
    Hello,

    Here are the current ratings for each device mentioned:

    SFR04:· 30~ to 50mA~

    Memsic:· less than 4mA~

    Transceiver:· 20mA~

    Parallax Servo:· 250mA~ no torque and 1000mA~ at full torque


    Dave

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Dave Andreae

    Tech Support
    dandreae@parallax.com
    www.parallax.com

    ·
  • steve_bsteve_b Posts: 1,563
    edited 2004-12-22 19:31
    So 1000mA is 1A at peak....so this isn't continuous, else your regulator would've cacked long ago.

    You still didn't mention what regulator you used.· But I'll assume it's something similar to what the BOE is using.

    I have the LM2940 on mine; this regulator will only do 1A.· So if you only have these in stock, you'll probably want to use a totally separate one for your servo.

    An LM340A will give you 2.4A peak.· Here's the sheet.

    I don't know, off hand, any other ones, but a search at any manufacturers website will get ya going!

    Google it or go to Digikey

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    ·

    Steve
    http://members.rogers.com/steve.brady
    http://www.geocities.com/paulsopenstage

    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
    pdf
    pdf
    lm340T-5.pdf
    828K
  • JiggsJiggs Posts: 26
    edited 2004-12-22 22:35
    Yes, the regulator I am using an LM2940. Thanks for the regulator specs, Steve. However, I am quite surprised that each survo could draw up to 1A. I'm powering everything with a 1.5A R/C battery, which, regulators aside, is obviously not enough to power 2 amps worth of servo. And Dave, thanks for those current specs.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    ~Jiggs
  • steve_bsteve_b Posts: 1,563
    edited 2004-12-22 23:03
    But that 1A is a peak value relative to the torque required to get over the starting friction of the gearing.·

    I'd be VERY surprised if that 1A is there continuous at full servo speed....but certainly you could expect a fraction of it to be there....at least half if not 3/4's.· Just a guess!· But you're batteries definately don't put out 1A continuous....they wouldn't last long at all.

    And just doing a quick look at the LM2940, it certainly is a 1A regulator.

    Like most ratings of components, you should design your circuits to a 60% level.· So if you're working with 12Volts, you're caps should at least be around 20volts.· So if you're playing with 2A's worth of toys and don't expect to add more current hogs, then you might want to be sure you have 3.2A worth of overhead.

    Doing a quick look on the digikey site, you might want to look at a TPS75501 which is an adjustable 5A LDO Regulator in a TO-220 package.· BUT, it's $8.80Canadian! haha·· It gets pricey....so if you have a few LM2940's laying around, then divide and conquer!!· Use a separate LM2940 for your servo's.

    Just a thought!

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    ·

    Steve
    http://members.rogers.com/steve.brady
    http://www.geocities.com/paulsopenstage

    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
Sign In or Register to comment.