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  1. hevans1944

    Make electronics : experiment 8 problem

    Thank you @Colin Mitchell for that clear and succinct explanation. One should also realize that after pressing the switch a certain pull-in current appears in the relay coil and that this pull-in current is always greater than the drop-out current, below which the contacts revert to their...
  2. hevans1944

    Make electronics : experiment 8 problem

    So which way is it? Does D2 stay lit and D1 flashes, or does D1 stay lit and D2 flashes? This circuit doesn't really teach you much of anything about electronics, does it? Except, maybe, it's not a good idea to try to energize a relay through its normally-closed contacts, because that is an...
  3. hevans1944

    Make electronics : experiment 8 problem

    Someone beat this horse to death more than three years ago in this thread. Also Google has a lot to say about it.
  4. hevans1944

    Considering viability of project: small wind turbine for 5 V camping charger

    And what would lead you to believe that driving the shaft of stepper motor would produce anything useful?
  5. hevans1944

    Sensing circuit for line following robot

    You STILL haven't provided us with part numbers or specifications for the infrared emitter and the diode infrared detector. Have you used your multimeter to measure the voltage at the cathode of the IR Receiver RX? Measure the voltage there with respect to GND with the light path both blocked...
  6. hevans1944

    Simple Circuit Problem

    You will need two diodes for each light with a current rating at least equal to what the light draws. So, if it's a 12 V lamp drawing 1 A and you have forty of them, you need eighty diodes each capable of holding off 12 V and conducting 1 A. A common 1N4001 silicon diode would work for 1A...
  7. hevans1944

    Triggering a Marx generator.

    The DC resistance of the ignition coil secondary winding appears to be shorting out the first stage of the Marx generator. You need a high impedance there, i.e., a spark gap, to allow the downstream stages to charge up. Then, when you create a low-impedance spark, it causes a domino effect...
  8. hevans1944

    I want help for my seminar

    It has its uses for short-range wireless communications over about a foot or two. Things like sharing data or images between two cell phones, or relaying sound to a pair of ear-buds from a NFC transmitter worn on the body. The NFC transmitter can get audio from a variety of sources such as...
  9. hevans1944

    Newbie Question......Suitable power supply

    You only need to operate one valve?
  10. hevans1944

    Newbie Question......Suitable power supply

    That's pretty close to the general idea. R1 and ZD1 could serve as the "dummy load" on the battery, with a comparator in the PIC performing the comparator function of IC1. Actually, many of the PIC comparators have internal references available so R1 and ZD1 aren't necessary. The two halves of...
  11. hevans1944

    Newbie Question......Suitable power supply

    Yes, except in your case it would fire up the transmitter and send a pulse to the receiver indicating "low battery" at pre-determined time intervals. Or you could mount a water-proof button on the transmitter case that would cause the μP to test the battery and light up an LED if the battery was...
  12. hevans1944

    Newbie Question......Suitable power supply

    Yeah, I can appreciate your feelings. It was years since I programmed a microprocessor when I ran across this thread here at EP. The idea of using a μP that cost less than a buck really caught my eye, so I ordered up a bunch of them (along with a PICkit 3 Programmer) and had at it. Man, what a...
  13. hevans1944

    Newbie Question......Suitable power supply

    Since your float switches will change state (open to closed or closed to open) very seldom, it is unnecessary to have the transmitter energized all the time. Even a 2.5 mA load, applied continuously, will drain a battery eventually unless the charge is replenished by some other power source...
  14. hevans1944

    Giant newbie, needs help regarding transmitter

    Gee, @Thomas_M if you don't want to go into full detail, then neither do we. Most of us here do not enjoy playing guessing games, trying to tease information from reluctant people who pop up here with vague requirements. Better to tell us up front WTF you want to DO and let us make suggestions...
  15. hevans1944

    Newbie Question......Suitable power supply

    @Gorhad I have been reading the Code of Federal Regulations (CFR) Title 47, Subpart 15, which governs the use of unlicensed low-power transmitters in bands that are otherwise licensed. Apparantly the original 70cm band transmitter you purchased is legal to use in the United States provided its...
  16. hevans1944

    Newbie Question......Suitable power supply

    Well, since you have all the parts, why not wire everything up and see if it works? If it causes interference and someone complains and you get a notice from the FCC, then you can go to Plan B. Just don't start cranking out a bunch of these as a "favor" until you get the legal ramifications...
  17. hevans1944

    Newbie Question......Suitable power supply

    Have you selected the float switches yet? How are you planning to install the switches in the pool (you mentioned mounting them to a bulkhead... what's that)? What length of cable will connect the float switches to the transmitter? Will you perhaps mount the switches in an open-ended PVC pipe...
  18. hevans1944

    Energy Monitoring (Formulas and methods help)

    For accurate AC power measurements you also have to account for the power factor of reactive loads like motors. That means measuring the phase difference between the current and voltage. IIRC, there are ICs available to do this automagically. If I remember where I saw them, I will post a link...
  19. hevans1944

    Newbie Question......Suitable power supply

    Are you looking to build something, or are you trying to find a commercial off-the-shelf solution? I am working with Arduino Uno modules and XBee (Bluetooth) shields. These can be setup for peer-to-peer short-range communication, but they do require some electronics and programming expertise...
  20. hevans1944

    Newbie Question......Suitable power supply

    I figured with your background experience being in Great Britain you would be unaware of the issue. The 433 MHz stuff is quite legal and popular on the other side of the pond. I don't think the Chinese (Region 3), who make most of the cheap stuff, give a fig who buys it or where it is used...
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