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Posts posted by wvengineer

  1. I'm doing a project for this plant...a wireless interface.  Anyways I'm also adding a low battery state alarm for remote nodes.  This will be implemented by using a LTC1440.  My problem is that  the output states are like 50mV and 5-9V.  I need to convert the 50mV into a negative 3-12V for rs-232 and it needs to remain a low power circuit so that the battery state doesn't drain the battery quicker than the modems.  Any low power converters that are popular?

  2. an IC can contain up to six gates, then why is it not possible to have different gates in a single IC? or is it? I've been looking at datasheets and i think haven't seen an IC that have multiple gates in them..

    If you just think of it as digital logic than you could use a programmable logic device.  Like a GAL chip or a FPGA where you don't worry about the gates so to speak but just come up with the logic expression using truth table, K-map, or whatever method you prefer.  I think in this case this is not what you want I just thought I would mention it though.  I think some FPGA's have a million gates...not sure, but I know the ones we used had tens of thousands of gates.  Neat stuff.  I also seem to remember being told that NAND gates are cheaper than AND so people would adjust their logic to use NAND gates for production projects to save money.  I also figure that whatever logic configuration is the most popular is what will be produced.  Sorry just rambling.   
  3. I know I was using that as an example as opposed to using a number that could possibly be someones ip.  That's why I said for example say my actual... I had thought about putting (I realize this is the local ip set by my router) after it, but I thought it would be assumed.  I've set up a network or two before  :). 

  4. First thanks for the replies.

    Staigen I'm pretty sure that my IP is dynamic not sure what it is at the moment.  I did manage to connect last night through a proxy service, but that's really slow.  The only thing that worries me is that maybe an ip block is banned right now for some reason.  For example say my actual ip was I believe you can block 192.XXX.XXX so all ip's that start with 192 would be blocked.  I hope this is not the case, but maybe it's just a DNS error, and I need to contact either the hosting company or my ISP.  I've checked everything I can think of on my side...blocked  sites, hosts file, router config, AV programs, and what not.  Hopefully it'll get straigtened out.     

  5. I have a problem.  For some reason from the house I can't connect to this site.  I'm at school at the moment.  I've done a tracert and I get through my ISP, but get stopped at defenderhosting.com.  I don't believe I've been banned or anything since I've only posted a couple of times.  I like this site and enjoy reading the posts so it kind of stinks I can't connect to it from the house.  Also this is the only site I can't conncet to.  Any help would be appreciated. 

  6. This is an older Projection TV that I actually got for free.  ;D
    I fixed it once ( a couple of resistors needed replaced) through luck that's why I got the TV.  I was hoping maybe someone had a copy of the service manual so I would have a better chance of keeping this thing running for awhile. 

    Thanks in advance.

  7. 2. Protection of motors from back emf using simple components like diodes & capacitors. ( Also could someone explain back emf in simple terms )


    Ok I did this pic in Matlab.  It's a simulation of a Series DC Motor.  Now the red line which I hand drew (imagine it as a smooth curve) would represent the Torque over speed curve. 

    To start off with this is how I understand it and how it was represented to me so take it with a grain of salt.  I'm in my last year of a BSEE curriculum.  Anyways the original pic is as labeled armature current over time.  This is from starting position to synchronous speed ( I did this awhile ago for a class).  Pay close attention to the armature current at the very beginning.  See that spike well that's when there is no back emf.  The armature current can't be that high for long or it would create heat and probably short motor windings.  When the armature of the motor starts to turn it creates a voltage that has an opposite polarity (back emf) with respect to the power supply.  As speed increases the back emf increases which reduces the potential seen by the motors windings (power supply minus back emf).  Which also reduces the current going through the windings as with the torque.  Torque is proportional to current as speed is proportional to voltage (red curve).  Anyways back emf is good.  When the load on the motor increases the speed drops, back emf drops, torque goes up and motor speeds back up (with in reason).  Any ways one concern is that controlling the motor by voltage will increase the current (red curve).  Remember decrease the voltage/speed increase the torque/current and current creates heat.  Anyways I know this is all over the place, but I hope it is understandable.  I got most of this from memory I didn't refer to my books so there may be an error here for anyone wanting to pick it apart.  ;D  Also if it's confusing let me know.
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