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  1. hevans1944

    DVM meters with Square waveform mode

    The link points me to a cheap imported 3 1/2 digit multimeter. Maybe the "unique build in square wave generator" could be used to stimulate a circuit? No information on what the peak-to-peak amplitude or current sourcing capability is, but for sixteen bucks (plus shipping and handling) I bet it...
  2. hevans1944

    Thermostaticizing

    Geez. Is there a problem making a connection to both secondary terminals of T2?
  3. hevans1944

    Logic set up times and hold times

    I think we may be focusing our attention too narrowly on clock pulse transitions versus data stability before and after the clock transition. This is usually not a problem unless the design logic is faulty or a component has failed. In the case of component failure, finding the failure almost...
  4. hevans1944

    Logic set up times and hold times

    If you have a two-channel o'scope you can use one channel to both trigger the horizontal sweep and display the edge of the clock signal. You need to have a fast enough sweep to see the interval a few nanoseconds after the clock edge. A delayed sweep is often helpful if it allows the clock edge...
  5. hevans1944

    Need a capacitor!

    Maybe, depending on whether your circuit really needs a non-polarized capacitor or not. If not, then it looks okay. You should try to find a schematic for your strobe, or failing that, try the motor-starting capacitor I recommended. You can solder wires to the spade-lug terminals to temporarily...
  6. hevans1944

    Need Help With Motion Sensor Controlled Strobe LED. II

    You don't HAVE to run it that hot (increase the value of the series dropping resistor), but the spec sheet does say 1000 mA maximum forward current, IIRC. Wiring D-cells in parallel is never a good idea. The strongest will discharge into the weakest. If you feel you need more ampere-hours...
  7. hevans1944

    No lead solder needs an 85 watt soldering iron

    Yeah, keeping those little SMT devices in place while blowing hot air over the board is a real PITA. No, the solder paste is usually at room temperature. I think even a perfect lead-free solder joint looks like a cold solder joint, which is why I exclusively use 63% Sn 37% Pb flux-cored solder...
  8. hevans1944

    Logic set up times and hold times

    If you are troubleshooting a logic circuit that doesn't work, or has intermittent problems, you measure the actual set-up and hold times with an oscilloscope to verify that they meet the device specifications. You trigger the scope on the clock edge that causes the flip-flop to change states, or...
  9. hevans1944

    Need a capacitor!

    Try this non-polarized "motor starting capacitor" available from Amazon, or visit the manufacturer's web page.
  10. hevans1944

    Need Help With Motion Sensor Controlled Strobe LED. II

    Yes, it would work. No, it would not be efficient. The cheapest current limiter is a resistor, but these unavoidably dissipate power. Try to choose a strobe circuit battery with terminal voltage only slightly greater than LED voltage, which is about 3 V. So a 4 V battery would be preferable to a...
  11. hevans1944

    Logic set up times and hold times

    Never. You get this information from the device datasheet and then make sure your logic circuit complies with the specifications.
  12. hevans1944

    No lead solder needs an 85 watt soldering iron

    Lead-free solder alloys melt at a higher temperature than lead-tin alloys. The amount of power needed depends on the mass and dimensions of the soldering iron tip. There is no "magic" in 60 watt versus 85 watt soldering irons. The higher wattage provides more power than the lower wattage, but...
  13. hevans1944

    Chop Mode and ADD Mode for Logic signals

    Chop mode is only effective for slowly changing logic signals. Add mode is marginally useful for monitoring two logic signals. A better instrument is a logic analyzer and a mixed-mode oscilloscope. Google these two instruments for more information.
  14. hevans1944

    How do I store energy

    Connect to the grid and sell your excess power to the utility. Cash, depending on bill denomination, can be very high-density energy storage.
  15. hevans1944

    Controlling a DC motor with a PLC

    Well, except for the missing connection from cathode of D2 to +5V, it looks okay. I would have expected to use a somewhat larger value for R1 and R2, but that depends on the voltage of the external power supply you use to energize the PLC relay contacts. Did you leave the 24 V DC supply...
  16. hevans1944

    decoder for 8051

    Learning how computers work by only reading a computer-theory book is like learning how to bake a cake by only reading recipes from a cookbook. It just doesn't work that way. Hands-on practical experience as you accumulate a sound grounding in theory, is the ONLY tried-and-true learning...
  17. hevans1944

    Controlling a DC motor with a PLC

    The CPU222 version has eight 24 V DC inputs and two sets of three SPST relay contact outputs, each capable of switching 2A in a voltage range of 5 to 30 V DC or 5 to 250 V AC. Each group of three relays has one contact of each relay in common, connected to the DC or AC supply (external) for that...
  18. hevans1944

    DC or AC Voltage reduction and relay help

    This multimeter has a polarity indication (-) if the red test lead is negative with respect to the black test lead. Swap the test leads while measuring DC volts and if you see the minus sign appear in the display, that is a good indication that what you are measuring is actually DC and not AC...
  19. hevans1944

    Building a simple radio scanner

    Software defined radios (SDR) are becoming more practical to build, and that would be my starting point for a scanner. Since the radio is defined by its software, adding a scanner function is almost trivial. However, you must define a reasonable portion of the spectrum to examine. Ten kilohertz...
  20. hevans1944

    Need Help With Motion Sensor Controlled Strobe LED.

    Do you need help in testing the PIR device? Do you know how to purchase, or build, a constant-current power supply to drive the LED? The title of your post implies you intend to rapidly flash (strobe) the LED on and off. How fast? How many on-off cycles per minute or second or whatever? How do...
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