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  1. hevans1944

    How to build a 455khz oscillator for a signal generator..

    Some pictures of the crystal in its little black box might help. The pictures in the Hallicrafter manual I found online are not very clear. No, a "more accurate" crystal is not going to help. You need to get the secondary of the IF transformer tuned to match the crystal you have. With the...
  2. hevans1944

    Designing a Time Delayed Relay

    Yikes! You removed all that wire and it still misbehaved? Perhaps exorcism followed by Indian sage-burning ritual will help... Murphy is downright persistent but can usually be evicted from the premises with vigorous efforts, some perhaps unconventional. Keep us posted on what you find. Don't...
  3. hevans1944

    IC Chip question.

    I keep a pair of duck bill pliers handy for this task. Grip an entire row of pins at once and bend them all gently inward. Repeat on the other side. For longer DIPs, repeat on each end.
  4. hevans1944

    Can you help me with ideas for an Electronic Project

    Can we discreetly help this guy without violating "homework" guide lines? Here is my suggestion: build a software defined radio (SDR) that tunes over at least two "bands" such as AM broadcast and shortwave broadcast. Add feature to select CW, AM, and SSB (upper and lower sidebands) and perhaps...
  5. hevans1944

    Designing a Time Delayed Relay

    Well... it didn't catch on fire or trip any circuit breakers, so there probably isn't anything wrong with the wiring. This sounds like the same problem you had earlier with the dust-collector relay operating immediately after power is applied. It is possible that all those wires are...
  6. hevans1944

    How to build a 455khz oscillator for a signal generator..

    I wouldn't go that far. This is just a very simple adjustment that requires the ability to set the RF excitation frequency applied to the grid of the previous IF stage very precisely. Not accurately, just precisely, and with some short-term stability while you tweek the core. You just need to...
  7. hevans1944

    Automatic ranging current sensing

    What happens to output uA when COMP goes high and turns on M2? What happens to COMP after that? There does not appear to be any provision for hysteresis in the comparator switching point. Just saying...
  8. hevans1944

    Diode question

    Always! There are a LOT of mathematical problems that do not have neat, analytical, closed-form solutions. Long before computers came along smart people developed iterative and piece-wise approximations that yielded "gud enuf" results for engineering and "guv'ment work". Today we have algorithms...
  9. hevans1944

    Diode question

    Thanks, Ratch. Easy peasy with that equation solver thingy. I knew I had seen this method somewhere before, but couldn't recall it. Nice touch adding the graph.:D
  10. hevans1944

    How to build a 455khz oscillator for a signal generator..

    Kenny, do you have this service manual? I doubt your Leader LGS-16 has the required 250 Hz resolution and stability to accurately find the crystal filter resonant frequency, which will be quite sharp and somewhere between 450,000 Hz and 460,000 Hz. Step 2 is adjusting the IF transformer...
  11. hevans1944

    Diode question

    Most of us here just assume the second term has a constant value of 0.7 V for silicon diodes or 0.3 V for germanium diodes. Various other values for LEDs depending on color and how they are manufactured. Current through a forward biased diode is an exponential function of the voltage across the...
  12. hevans1944

    help connecting 555 timer

    Someone on this forum has ESP (being somewhat older, I forget who...) so maybe they can chime in with a revelation of what the OP is trying to DO. For example, I thought from what I read in post #1: that each sensor was triggered on for 1.0 seconds with a delay of .01 seconds between sensor...
  13. hevans1944

    help connecting 555 timer

    It's a start. More information is necessary. What is the nature of the "special miniature infrared sensors" and does each produce some sort of analog or digital output that you need to measure or record individually? A datasheet describing the sensor would be helpful. Does the seven-foot long...
  14. hevans1944

    DIY Surface Mount Assembly

    In the next few months I will attempt to modify a Black and Decker toaster oven for re-flow oven soldering. Plenty of advice on the Web on how to do that. The stencil is a very good idea and you can order them inexpensively. If you are going to dispense solder paste manually, I would go with...
  15. hevans1944

    help connecting 555 timer

    Well, it might help you in preventing electrical fires. :D It gets better with some hands-on experience. Keep reading, and re-reading, as you perform experiments on a prototyping board (you do have one of these, riiiigt?) with a single 555 and a handful of resistors and capacitors. Helps to...
  16. hevans1944

    Help with connecting&controlling THK kr20 Linear Actuator

    What did you expect to happen? Vdd and GND are there to supply 5 V DC to the electro-magnetic encoder. The encoder consists of a magnetic disk, mounted on the motor shaft, that is magnetized around its circumference with alternating north and south poles that pass by two Hall-effect sensors as...
  17. hevans1944

    What can you tell me about paper capacitors?

    Geez, Dave... you are OLD!:D I remember my first encounter with molded inductors, too. Couldn't make out head nor tails of what the markings meant, so probably just "filed" them away as miscellaneous as I was salvaging parts from discarded radios and televisions in the 1950s to pursue my...
  18. hevans1944

    LED pucks getting hot

    You could also try placing one or two forward-biased diodes in series with the power pack output to drop the voltage presented to the puck lights.
  19. hevans1944

    What can you tell me about paper capacitors?

    Actually, ALL the capacitors in Edd's post are wax-impregnated paper capacitors. Don't be fooled by their encapsulation in plastic.
  20. hevans1944

    What is the best Program to Design PCB

    They ALL require climbing a steep learning curve. The more expensive programs do a lot of housekeeping for you and may have better "automatic" wire routers. It is best to purchase a program with integrated schematic capture that is backwards-linked to the PCB layout function. All of them are...
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