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  1. chopnhack

    Designing a Time Delayed Relay

    I found a 2w 12v zener diode http://www.digikey.com/product-detail/en/DZ2412000L/DZ2412000LCT-ND/3594986 I understand the concept of linking the diodes in series, they would effectively share the job of dissipating the heat from the circuit in a similar fashion to lower wattage resistors in...
  2. chopnhack

    Designing a Time Delayed Relay

    Wow, Kris! Thank you for your efforts. I wasn't sure if it was a good idea or not! I will look into the diodes tonight. Some questions before I begin, why SMT for the diodes? I have found several 1W or greater 12v zener diodes, so I think they will be able to dissipate the energy required, but I...
  3. chopnhack

    May I tell you about my free book?

    I'd be more than happy to Steve. I will do so once I completely finish reading!
  4. chopnhack

    May I tell you about my free book?

    That is really awesome Steve!! I had seen references to making an O scope with your PC before, but had dismissed them because of potential damage to the pc. Your remark about using your laptop sparked the idea in my head! I didn't think I could use my laptop :) I have an older unit running vista...
  5. chopnhack

    Designing a Time Delayed Relay

    I got RθSA from Aavid's catalog :thermal resistance from mounting surface to ambient or thermal resistance of heat sink in C per watt. Aavid's catalog has the equation I was trying to use on page 9 http://www.aavid.com/sites/default/files/literature/Aavid-Board-Level-Heatsinks-Catalog.pdf The...
  6. chopnhack

    Designing a Time Delayed Relay

    I have been looking at that on and off today to try and figure out the RthetaSA of the 78M05 TO-220 package. I came up with the figure of 130deg C/Watt which doesn't make any sense. I am sure I am just doing the math wrong... I was using 0.75W of power to be dissipated, 2.5 deg C/W for Rtheta...
  7. chopnhack

    Designing a Time Delayed Relay

    Sounds ok, I just dont understand how I could fit the required heatsink surface area on the board - even if I used both sides with thermal vias, we are talking about using 1 sq in. per side as a heat sink - the entire board is less than 15 sq inches! That is a lot of real estate on a pretty...
  8. chopnhack

    Designing a Time Delayed Relay

    Thanks Kris. A 30 degree rise would be fine, that would essentially be slightly above ambient temp. - however after reading http://www.ti.com/lit/an/snva419c/snva419c.pdf I see some difficulty cramming all this into a 10cm or smaller PCB! The link states that the theta figures are based on JEDEC...
  9. chopnhack

    Designing a Time Delayed Relay

    Regarding thermal dissipation - the 78M05 datasheet says that the RθJA is 92 deg C/W. Does that mean the IC would approach roughly 65 deg. C? Being in an enclosed box, I think that is fairly hot. Would it be a good idea to put a buck converter in front of the v. regulator?
  10. chopnhack

    Bench Power Supply

    Not really sure if I would need something that low, but you read various accounts and then it seems like a good idea! Good point Dave, the LM350 would be a better choice, thanks for that thought!
  11. chopnhack

    Bench Power Supply

    Thanks Solarwind, in retrospect, I believe for my first psu, 1.5A per channel should more than suffice. I have given a great deal of thought into what features I would like. I have read various information and I am now debating the merit of starting at 0V. Do you think I should worry about...
  12. chopnhack

    Hypothetical Question on Potential and Resistance

    Thanks Bob! It's getting clearer :) Awesome Steve!! So for LEDs controlling the current is far more important than the Vsupply - and that is only by virtue of the device being a modified diode. I think I get it! Thank you!
  13. chopnhack

    Got a question about driving LEDs?

    Old or not, I found it most enlightening ;-) It may raise more questions and I am more than happy to proof read it. Thanks for taking the time to upload it and continuing to answer questions.
  14. chopnhack

    Got a question about driving LEDs?

    Awesome Steve!! Typo under caption of 1.1 : I think you meant it's <<This uses Vs and Vl instead of V and Vf, but it'd just alternative labelling.>>
  15. chopnhack

    Hypothetical Question on Potential and Resistance

    Now with that in mind, would the LED be burnt out by excessive voltage? Is that the right way of thinking of this? Or by controlling the milliamps running through the LED would we keep the device safe? Another train of thought says its more complicated and needs to account for the total power...
  16. chopnhack

    Hypothetical Question on Potential and Resistance

    Thanks for confirming that Steve :-) 120v 2.4W - sounds a bit impractical but doable. I guess a large ceramic type resistor or a wirewound could handle that much energy disapation. 600v 12W - impractical, certainly would want to convert power with a step down transformer first. Would the...
  17. chopnhack

    Hypothetical Question on Potential and Resistance

    A thought occurred to me the other day while I was reading some posts and looking over some schematics. I thought I might have understood the function of resistors in the scheme of things, but just like that, it seems to have eluded me... If we had 120v DC potential across two wires and tried...
  18. chopnhack

    Logic gates

    Great article so far - I think the explanations of the gates is clearly presented - at least clearer than I have read about them in the past, especially how you treat the NAND gate, AND followed by NOT! I did lose you at "meaning that all another logic gates can be constructed form NAND gates"...
  19. chopnhack

    Arduinos combined to be a gift?

    LOL, experiment on your own time bub :-) The Mrs. must get her present on her date of birth, otherwise you may get the couch... you have been warned, good luck!
  20. chopnhack

    Terminal voltage sensing

    Nothing to add re: sensing V, but I read in a unrelated article, when batteries approach full charge, current decreases to nearly 0. Maybe it would be easier to sense when there is no current flow (or a predetermined lower level of current flow) as an endpoint to the charge cycle.
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