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  1. hevans1944

    Noob Soldering Problem - Which Wire To Use?

    Chris, I once had one that I had (by trial and error) set for 30 AWG wire-wrap wire. Used that tool a lot back in the day, but one had to develop a "knack" for squeezing, slightly twisting, and pulling the insulation off without nicking the wire-wrap wire. Hopefully I will never have to do that...
  2. hevans1944

    Noob Soldering Problem - Which Wire To Use?

    I have used the Miller stripper for years also, but prefer the precision round-hole type. The Miller V-jaws require some skill to either set properly or "feel" properly. The Air Force issued me an abomination that had a complex mechanism that gripped the wire as you closed the handle grips, then...
  3. hevans1944

    Noob Soldering Problem - Which Wire To Use?

    From your description of "a very thin wire" and the fact that it breaks, it is obvious you are using a single strand of solid wire to make the connection to your CR2032 battery holder pin. There are two frequent problems that occur with this practice: tiny nicks in the wire caused by poor wire...
  4. hevans1944

    Need recommendation for rheostat or potentiometer

    This is an example of applied engineering. It is important to specify components of a design completely and then select particular components that meet those specifications. In this case you originally chose a motor and fan combination that met the air flow and pressure specifications but failed...
  5. hevans1944

    Need recommendation for rheostat or potentiometer

    Amen to that! Gotta stay with the rules AND have fun! Please measure the current applied to the pusher motor at your full battery pack voltage. The product of the voltage and current will tell you what the maximum power consumed by the motor will be. Any resistors you place in series with the...
  6. hevans1944

    Need recommendation for rheostat or potentiometer

    Chris, @NyeSpy in his post #20 posted a verbatim copy of part of the rules for the competition. With a little help from Google I was able to determine that this came from the rules for the 2017 Science Olympiad. The rules are protected by copyright so I won't post them here. Despite the...
  7. hevans1944

    Need recommendation for rheostat or potentiometer

    You are NOT all set on that front. Controlling the volume of air produced by the "push fan" is the problem, and your "solution" is to starve the fan for power to slow it down with a variable resistor. That's right up there with controlling the speed of an automobile with the brake pedal while...
  8. hevans1944

    Extraction Automation Complete!

    Yeah, $2.55, even with shipping and handling added, is a no-brainer. Good find @boyd!
  9. hevans1944

    Electromagnet project

    Unless the motor armature (the part that rotates and interacts with the electromagnets) turns very slowly, you need a fast-switching H-bridge for each electromagnet. And some means to control the back-emf that results when the current is switched off or reverses direction. You will probably...
  10. hevans1944

    What the latch?

    Yes. I frequently use one for just that purpose when prototyping with 5 V TTL logic devices. If you use CMOS logic devices, they can be powered directly from your 9 V wall wart. Or you can "roll your own" flip-flop from discrete components as Minder suggested.
  11. hevans1944

    American Electronic to Australian

    You might also consider visiting (or calling or sending an e-mail to) the manufacturer of your turntable to get their advice on (1) using a step-down transformer and (2) determine whether the difference in power line frequency is a problem. As Minder suggested, sometimes just the change-out of a...
  12. hevans1944

    Electromagnet project

    Actual circuitry as well as the "electromagnets" you plan to use will depend a lot on the timing details... how fast you want the current to rise, how fast it must fall, the interval between successive energize commands, when (and how) you plan to "reverse polarity" and for what purpose. Please...
  13. hevans1944

    LEM HLSR 10P current sensor

    Clever idea, but the diodes defeat the ultra-low resistance (a few milliohms) for which this type of device was created. Should work though if one can "tolerate" the voltage drop across the bridge and subtract the DC offset in the output.
  14. hevans1944

    100G ohm resistor only measures 50G ohm

    I would give in to the temptation, just to see whut hoppens. Well, maybe I would want to have an untouched spare, in case something awful happened. If there is factory-applied identification on the outer glass envelope, it is possible this could be worn off, dissolved, or otherwise erased after...
  15. hevans1944

    100G ohm resistor only measures 50G ohm

    Did you clean the glass envelope of your 100 GΩ resistor? I would use a mild dish-washing detergent in de-ionized or distilled water followed by an 90% isopropyl alcohol rinse and careful drying. Use nitrile gloves to handle it and a fresh Kimwipe or a hot-air gun set to a low temperature to dry...
  16. hevans1944

    LEM HLSR 10P current sensor

    Please bear in mind that this transducer is similar to the Allegro Hall-Effect sensor. It responds to both positive and negative current directions through its input terminals, with an offset of about 2.5 V DC when the input current is zero. Thus an AC input current will cause an AC output with...
  17. hevans1944

    Need advice for a simple circuit, please...

    You will need to connect all your valve outputs to a common manifold and arrange to purge the manifold between substances. You need to especially avoid mixing acidic and alkaline fluids because of the (usually) violent chemical reactions that results. That means that a purging fluid, such as...
  18. hevans1944

    Circuit design help for blind dog

    That's a good point, but unless the power source is a super-capacitor (and how toxic are those?) a battery would be a requirement. That means the whole shebang needs to be potted in an epoxy the dog cannot easily defeat and the play closely supervised. Wireless inductive re-charging is...
  19. hevans1944

    What's this ?

    Looks like it might be an International Rectifier IRLR7843 Hexfet. Have you started a "what is it" thread here? If so, each "whutizzit" should be a separate topic, i.e., thread.
  20. hevans1944

    TTL logic based Question

    Thanks, Harald! That link you provided has a wealth of information on how TTL circuits were implemented, things I haven't visited in more than forty years. You are a fountain of good information!
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