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  1. hevans1944

    capacitance value to add delay in circuit

    Gee, you are using a raspberry pi to activate a relay? Surely you can program the delay you need instead of using old school analog technology?
  2. hevans1944

    I need something that is LOUD ,but is still small ,and lightweight. HELP!

    Welcome to the Forums, Daisy! I would mount a small inexpensive loudspeaker, about four or five inches diameter, in the hollowed out foam hammer head. Maybe mount two of them if the head is like a sledge hammer with two faces. Yes, drill plenty of holes in the foam to let the sound out. Run the...
  3. hevans1944

    Need Help With Motion Sensor Controlled Strobe LED.

    Gee, is your Google search function broken? The Luxeon SP-02-N4 is a single LED module that requires up to 1 A of DC with a compliance voltage of at least 3 V. A constant-current power supply is recommended. The CEG007100 is surplus OEM product imported from China. It is rated to operate from...
  4. hevans1944

    Sound Frequency-based power switch

    You have specified a particular audio frequency to four significant figures: 146.8 Hz, which happens also to be musical note D3 on the equally tempered chromatic scale used in America (and elsewhere). Is there some reason for selecting this particular frequency? Please realize that there is...
  5. hevans1944

    thermostat circuit counter

    I was going to suggest finding the furnace transformer and running a twisted-pair from its secondary along side the thermostat pair, just to avoid having to install a transformer to operate the relay. Technically, since one of the thermostat wires is already connected to one terminal on the...
  6. hevans1944

    thermostat circuit counter

    The point is this: the transformer supplies power to whatever load the internal control circuitry of the furnace presents to the transformer through the thermostat switch. This is a series circuit consisting of the transformer providing power to the internal control circuitry of the furnace in...
  7. hevans1944

    thermostat circuit counter

    You are free to wire it up any way you like, but if you want it to actually work, you have to use the thermostat contacts to operate a relay... which is probably what they already do in the furnace. The two wires going to the boiler controller are NOT a source of power for your elapsed time...
  8. hevans1944

    holographic live video

    Perhaps this is what you are considering.
  9. hevans1944

    Power supply noise.

    The pi-network gets its name from the appearance of the components on a schematic: two capacitors from the output to common with a small inductor inserted between the capacitors. The inductor knocks down (attenuates) the high frequency ripple and noise while the second capacitor shunts them to...
  10. hevans1944

    Help with Intercom Circuit

    10 to 20 μF aluminum electrolytic rated for at least 16 WVDC, if needed, would be okay. Positive terminal to collector of T2, negative terminal to ground. On electret microphones: some (most) of these have a FET inside the case to convert the very high impedance of the electret element to a...
  11. hevans1944

    Power supply noise.

    Have you tried a pi-network filter on the negative buck converter output? Also you need to pay attention to ground return paths: you don't want the buck-converter input return path anywhere near the ADC analog common. Is there a PCB layout, or are you in the prototype stage?
  12. hevans1944

    Help with Intercom Circuit

    Looks okay to me. I assume DC power comes in through SL1. Not sure what the purpose of R3, 560 Ω resistor, is and why the collector of T1 doesn't have a bypass (filter) capacitor.
  13. hevans1944

    Creating my own transformer

    Skin effect never goes away, even at low frequencies such as 50/60 Hz power line frequencies. Utility high voltage overhead transmission lines typically use a steel core (for strength) under aluminum cladding. I am sure they would use silver or even copper cladding if that were economically...
  14. hevans1944

    Help Flexible Flat Cable Connector

    This looks like a PCB edge-connector socket with some sort of retention mechanism on the ends. Is the cable attached to a PCB paddle board? Unless there is hardware (latches, whatever) on the mating piece, it does not appear that there is anything on the socket that would allow you to "open it...
  15. hevans1944

    Why I haven't been posting too much this weekend.

    My wife bought one of these contraptions last year because we are moving toward an organic veggie diet. They do have a plastic thingy with sharp metal spikes protruding from it that is supposed to be used to hold food (in lieu of using your hand) while slicing. Eschewing the device because it is...
  16. hevans1944

    Creating my own transformer

    Can you upload a picture of the transformer core that you have? I used to salvage transformers from old television sets and try to rewind them... but that was fifty-something years ago. The hardest part was separating the "E" and "I" laminations because they were shellacked together, each "E"...
  17. hevans1944

    ID please

    VZxxxx isn't much help. They look like small-valued capacitors, but could also be MOV varistors used for surge protection. Most varistors I have seen have the leads welded to opposite sides of the disk though, so your guess is as good as mine without electrical testing.
  18. hevans1944

    thermostat circuit counter

    See my previous post #6. You need to separate the thermostat contacts from the two wires going to the furnace and replace them with a relay contact. The thermostat will then operate the relay and the elapsed-time meter as well as the totalizer without these devices interfering with normal...
  19. hevans1944

    thermostat circuit counter

    Most thermostats on commercial heating systems operate from low-voltage AC, typically using a low-voltage door-bell type transformer. On an integrated HVAC (Heating, Ventilation, and Air Conditioning) system there will be separate circuits for heating, cooling, and the air circulation fan. It...
  20. hevans1944

    Creating my own transformer

    20 cm x 20 cm x whatever thickness is a pretty big core. If its 20 cm x 20 cm x 20 cm it will weigh a lot. You should be able to purchase grain-oriented silicon steel laminations, stamped for either an "E" core or a "C" core, of that size. Just Google transformer cores. You need a bobbin to...
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