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  1. hevans1944

    Help with optical sensors

    Why not use the circuit below, copied from the application note that @Merlin3189 linked? It's a good place to start even if you don't use the logic gate.
  2. hevans1944

    RCD Problem

    I would find a three week period when you are NOT on holiday, or otherwise not available to check on the incubator, and charge your child with the task of daily checking the condition of the incubator during that time interval. At the end, if the eggs were fertile, you should be rewarded with a...
  3. hevans1944

    Low tension ignition inductor

    Are you restoring an automobile or internal combustion engine from this era? Low-tension coils are not hard to make. You can "guesstimate" the inductance by using an ordinary inductor in place of the "real deal" until you obtain an acceptable spark. I would start with something on the order of 1...
  4. hevans1944

    Running high current electric solenoid using a H-bridge

    If the engine is running, the short high-current pulse sent to the solenoid will be quickly replaced by the alternator charging the battery. No worse than turning your headlights to high beam IMO. You could also consider adding a large electrolytic capacitor to store enough charge to activate...
  5. hevans1944

    power supply

    The circuit you have encircled in red provides a negative rail, with respect to the output "common," for the op-amp. This allows the op-amp output to go to zero, and negative, with respect to "common" when the potentiometer, R5, connected to the non-inverting op-amp input is set to produce zero...
  6. hevans1944

    Zeroing out a LM317 reference voltage with a zener - PSU build

    A zener diode behaves exactly the same as an ordinary diode except the reverse voltage rating of a zener diode is the zener voltage. The reverse voltage rating of ordinary diodes can be just about anything, but heavy doping of the PN junction produces a specific reverse breakdown voltage for...
  7. hevans1944

    Oscillator or Not?

    Wow! Are you perhaps using this instrument? Have you calibrated it yet? Checked the orientation of its sensor with respect to an external electromagnetic field? What is the principle of operation? Does it respond only to magnetic fields, perhaps using a Hall-effect sensor? How will you determine...
  8. hevans1944

    "Lightpole" Project

    So, lemme see if I got this right... You have two accumulating interval counters associated with A and B lamps. Both counters are initially reset to zero. When a lamp is on, its associated interval counter is running. When a lamp is off its associated interval counter stops running but does not...
  9. hevans1944

    hi i need alittle help here

    Maybe a small trap-door on the bottom of the can would work. When the quarter lands on the bottom its weight opens the door downward. A sensor detects when the door opens and lights the red light. Circuit for detecting that the door has opened could be either a manual reset or a time-delay to...
  10. hevans1944

    Oscillator or Not?

    Welcome to Electronic Point! You start by specifying IN DETAIL what you are trying to DO. What is the purpose of the bar you want to wrap with copper wire? Is it supposed to DO something when you close the "master switch?" What material is the bar? Iron? Steel? Plastic? Aluminum? Wood...
  11. hevans1944

    Standalone Clock

    Perhaps something from this vendor will suffice...
  12. hevans1944

    Decade voltage regulation box

    You can use a programmable three-terminal regulator, such as an LM338, and drive the programming terminal from a digital-to-analog converter to create a computer-programmable voltage output. Or use discrete transistors driven from logic-level outputs to select the output voltage: Above...
  13. hevans1944

    AM transmitter

    This isn't easy since you know absolutely NOTHING about the magnetic characteristics of the ferrite rod, nor have you specified a variable tuning capacitor that you would use to resonate the "right mhz" unless your post of "capacitor - 472" refers to a 472 pF air-variable capacitor. If you can...
  14. hevans1944

    Thermocouple RF Ammeter

    Yeah! That's the meter movement most hams would use! Who invented this? How long has it been around? The meter movements are quite popular items on the Web because any idiot can build a directional coupler... no electronics experience required if you can follow directions. Well everybody's...
  15. hevans1944

    AM transmitter

    Also, "Never bring a ferret (glued or not) to a gunfight; bring a Gorilla and/or a gun." Elmer Keith would (probably) say that if he were still alive.
  16. hevans1944

    Running high current electric solenoid using a H-bridge

    Your reply about this being a motorcycle engine and transmission fitted for an automobile got me to thinking that maybe two conventional solenoids with free-floating armatures mounted on opposite sides of the shifting lever might work. In the de-energized position, the spring-return to center...
  17. hevans1944

    AM transmitter

    And be sure to use genuine ferret glue, not that gorilla glue stuff because it expands and makes a mess.
  18. hevans1944

    Thermocouple RF Ammeter

    Yeah, I just might score one at the Dayton Hamvention this year if the price is right. I have this strange attraction for D'Arsonval meter movements, with or without a mirrored scale for parallax error prevention.
  19. hevans1944

    Thermocouple RF Ammeter

    All the more reason to locate the watt-meter as close as possible to the antenna feed. It IS very portable. And make sure you are using the right "slug," Type D or Type E for UHF.
  20. hevans1944

    unused op amp

    It is always wise to follow device manufacturers "suggestions" when attempting to apply their product. Presumably they know more than you do, even if they don't respect the need to save big bux and precious PCB real-estate by eliminating two resistors. If you buy this part from Microchip, their...
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