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HB25 start up... question and perhaps a solution. — Parallax Forums

HB25 start up... question and perhaps a solution.

DgswanerDgswaner Posts: 795
edited 2008-01-01 09:14 in Propeller 1
I got my HB25 they work great all is well, but in order to get them to work I have to cycle the power to the motors (not the HB25) this was expected as per the documentation. I however do not want to have do this every time I start up this bot, especially since I want it to be web controlled.

First off this is normal right? I'm not providing the proper start up time for the HB25 so I need to reset the power to the motors to make up for it.

My thoughts, I want to run the power through the NC side of a relay, and the first thing this bot will do is to activate the relay pulling the connection open. (resetting the power) after a few other items have been run allowing the start up time, I can shut off the relay the motors should work and no extra power is used to for the relay. Sound like a good idea? too simple? to complicated? any thoughts?

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

DGSwaner

Comments

  • dwbowendwbowen Posts: 30
    edited 2007-12-31 22:49
    Hi DGSwaner,

    I was thinking about doing something similar with my HB25s so that the whole system can be powered up using one switch and include the delay required for the HB25. So, I do think this is a good idea... Although I have no technical advice to offer you, I do have a question. What type of relay are you planning on using? I cannot seem to find one that will work with the voltage of the stamp and switch the voltage required for the HB25... any ideas?

    thanks

    david bowen
  • deSilvadeSilva Posts: 2,967
    edited 2007-12-31 23:19
    Relais exist mainly for 12V (a host of choice), some 5V types and very few for 3V3. To operate a relais you need a certain amount of power ( >150 mW) which is the main issue. This leads to needed current of >50mA for 3 Volts and this will generally not work from a microcontroller pin without an intermediate transistor or driver (as ULN2803) . This however is very simple to interface.... 12 V is highly recommended when any releais are in the game...

    The problem (=size/volume/weight) of relais is not so much the swiched voltage but current. 120VAC works with many (in contrast to the 220V in Europe where 1/2 of nice relais cannor be used, as they are rated for 120VAC only.)

    "Solid state" relais have a different price tag...
  • DgswanerDgswaner Posts: 795
    edited 2008-01-01 04:44
    I was planning on using a 12v relay, I have a few on hand. the coil amperage does exceed the I/o pin, I haven't worked out the details of the circuit yet. but I was thinking about a 2n222. Transistor. I haven't checked all of the specs yet but I think it can handle it. I'll likely work on this next year! (hehe tomorrow). and I'll let you know how it goes.

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

    DGSwaner
  • deSilvadeSilva Posts: 2,967
    edited 2008-01-01 09:14
    Dgswaner said...
    the coil amperage does exceed the I/o pin
    True smile.gif
    Though the coil impedance is around 1k for a low power 12 V relais, it goes down to 100 or even lower for 16 A relais.
    But many transistors can drive 300 mA; that needs no special selection...
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