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  1. hevans1944

    Building a current source

    This sounds suspiciously like a homework assignment. PID is short for Proportional, Integral, Derivative and is part of automatic control theory. Below is a block diagram of this linear process, extracted from the web page just cited.. The box labeled Plant/Process can be just about anything...
  2. hevans1944

    Building DIY Vacuum tubes

    Me too! A very welcome indeed to EP, George! I am sorry I cluttered up your thread with my reminiscing. It seems there are a lot of hobbyists out there reproducing triode vacuum tubes, so your efforts are certainly appreciated here. I would love to encourage others to do similar things...
  3. hevans1944

    Bought a cheap soldering iron - should I be concerned about this?

    If it works for you I wouldn't say it's garbage. Inexpensive, sure, and maybe of questionable quality, but the question you should ask yourself is: does it solder? You can add lots of fancy bells and whistles to a soldering iron, but if it doesn't get too hot or too cool and you can tin the...
  4. hevans1944

    Building DIY Vacuum tubes

    Working, yes, but high performance... probably not. I grew up puttering around with vacuum tubes before I was a teen-ager, and learned to appreciate the complexities of them before getting involved with semiconductors in the 1960s. In the Air Force I worked on defensive fire-control systems that...
  5. hevans1944

    Building DIY Vacuum tubes

    Before I "retired" I usually purchased DC-704 silicone diffusion pump liquid from Kurt J. Lesker, but a 500 ml bottle (enough for one large Varian) was somewhere around US$100. Other workers in my lab opted for the more expensive grades, thinking this would improve the vacuum in their systems...
  6. hevans1944

    Building DIY Vacuum tubes

    I once worked with a scientific glass blower who made his own quartz-enclosed mercury diffusion pump for high-vacuum pumping, backed by a belt-driven Welch vacuum pump. I tried to stay away from his lab for fear that I would accidentally breath some of the mercury vapor, but the risk was...
  7. hevans1944

    How to draw this?

    On the Cartesian coordinate system, the vertical axis represents reactance. Positive reactance is inductive reactance. Negative reactance is capacitive reactance. The horizontal axis represents resistance. Positive resistance is on the positive horizontal axis. Negative resistance is normally...
  8. hevans1944

    Building DIY Vacuum tubes

    Your biggest problem will be obtaining (and holding) a really good vacuum. Are you planning on using a filament-heated getter after pump-down and seal off? Those pesky electron critters don't like colliding with residual gas molecules, although it does make for a nice glow with appropriate...
  9. hevans1944

    +/- 12 V power supply acting weirdly(?)

    It would be better, IMO, to create the "floating" ground at the input, between the terminals of the (hopefully) floating 30 V supply. A pair of low-valued resistors will do it at the expense of a lot of wasted power. Another approach is to use a power op-amp output as the "floating" ground...
  10. hevans1944

    need help regarding tilt alarm

    Looks like a 3-axis accelerometer sensor with LED readouts for ±error indication, processed from roll, pitch, and yaw accelerometer outputs, would work. Point the drill in the right direction, press a button to store initial accelerometer values. If deviation on two axes perpendicular to the...
  11. hevans1944

    PWM - pic18f4550 - led + potentiometer

    I don't do C much, but there should be a way to import those libraries into MPLAB. Try asking on the Microchip MPLAB XC8 forum. Might want to look at some of the links here too.
  12. hevans1944

    2 Graphics Cards 1 Problem

    Without a set of schematics, a test fixture, an oscilloscope and a logic analyzer it looks pretty hopeless. Have you tried contacting the manufacturer(s), who will have all these things plus experienced technicians, to see if they will repair the boards at a reasonable cost? It's sad that so...
  13. hevans1944

    PWM - pic18f4550 - led + potentiometer

    @Bellon do you want to program the PIC using C or assembler?
  14. hevans1944

    +/- 12 V power supply acting weirdly(?)

    You did notice that in the application circuit, Figure 16, that a bi-polar +20 V and -20 V with respect to circuit common or ground was used? The circuit you built does not do this. If your 30 V supply has its negative side connected to the input of the 7912 negative regulator and its positive...
  15. hevans1944

    Tilt and swivel antenna mount

    That would be awesome... you could do drive-bys looking for WiFi hot spots. Is this thingy mounted inside the campervan or somewhere exterior? How would you propose weatherproofing the tilt and pan mechanism if mounted on the outside of your vehicle?
  16. hevans1944

    Control large stepper motors

    Wow, Chris! What a wunnerful idea! Totally agree, just not sure how to make that happen. Not saying Google doesn't return links to Electronics Point, but it's hit-or-miss unless you have a well-crafted search string AND the topic has appeared here in the forum. For example, for the link I...
  17. hevans1944

    Control large stepper motors

    Google is your friend (or should be before coming here). Check out the search results on this page. Come back here after you have made your selection or design approach. I am sure you will have some intelligent questions. BTW, a 4V 4.4 A stepper motor is not a particularly large motor. Do you...
  18. hevans1944

    LM741 amplifier

    Well, actually it doesn't have to be ±12 V DC. But it does get more complicated if you want to use a uni-polar power supply instead of a bi-polar power supply. Read this Texas Instrument Application Note and then come back here with more questions if you don't understand it. Visit this site and...
  19. hevans1944

    Curious inductor question

    No load? How do you know the output increases with frequency? If measuring the output with an oscilloscope there is still a load, usually about one megohm shunted with twelve picofarads or so of capacitance. This will form a resonant circuit with your inductor. More information, please, before...
  20. hevans1944

    Convert 15v turntable to 12v

    Psychic is good. I live with one every day. Her favorite remark to me is, "I told you so!" And I do love it when a newbie pops in with one post and then goes on vacation without further comment while receiving ten replies. Gives me a warm fuzzy feeling all over to know how much good this forum...
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