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  1. hevans1944

    Question on assembly code

    Well, good luck getting that board full of parts to play together nicely. Personally, I would have started with the Intel 8085 microprocessor. How do you plan to locate the 32 kbyte ROM in the 64 kbyte address space? What address range will your RAM occupy? How much RAM will your single board...
  2. hevans1944

    Reducing noise from sensors and implementing multiplexing system

    Gee, is this a classroom assignment? Are you actually expected to design, build and demonstrate something that works? Who gave you those "design specifications" and why are they so vague and lacking in specific design goals? I agree with @Laplace: it looks like you have jumped into the shark...
  3. hevans1944

    Carver PM-420

    There appears to be a popular forum for Carver owners. Perhaps you could join and get some advice. It appears to me that someone butchered your amp. Probably all you need to do is restore the input jacks to their original configuration.
  4. hevans1944

    Regenerative Circuit

    Regenerative circuit? Not. These are two "crystal set" AM radios with two stages of audio amplification. And where do you see any "3v lithium ion batt" or "simple green LED" anywhere?
  5. hevans1944

    Back EMF protection

    Sometimes we include a low-valued resistor in series with the diode to dissipate the energy stored in the magnetic field of the solenoid. This will also help speed up the solenoid current decay.
  6. hevans1944

    problems encountered when building an analog computer for simulating 2nd order diff eq

    Welcome to Electronics Point! And congratulations on your decision to explore the fascinating world of analog computers. There is still a lot of interest in this "obsolete" technology which can perform real-time simulations of complex physical systems. Unfortunately, my last relevant experience...
  7. hevans1944

    OpAmp oscillator circuit

    I think what Adam is saying is the following stage (which he didn't show) uses the triangleish wave across C1 to compare with a DC reference to create the PWM waveform... or sumthin' like that. What the heck is the round thingy the MOSFETs are trying to drive? Arrgh! I said I wouldn't waste...
  8. hevans1944

    Charlieplexing 64 Switches

    Charlieplexing is good only for lighting ONE LED at a time in an array of LEDs. It takes advantage of the diode characteristic of an LED to allow two LEDs connected in anti-parallel to illuminate independently, but not simultaneously. Read the Wikipedia article for enlightenment. The article...
  9. hevans1944

    OpAmp oscillator circuit

    Clarification: TWOFT = Total Waste Of Free Time
  10. hevans1944

    OpAmp oscillator circuit

    No, Harold, the OP should have spent more time with the schematic. And perhaps explained what this circuit was supposed to do, if it actually worked. TWOFT to spend any more effort trying to "analyze" it.
  11. hevans1944

    Best solder to use

    For tinning wires, nothing beats an old fashioned solder pot. Here the admonition not to use flux does not apply. I always kept a tin of non-corrosive resin flux handy to keep the molten solder clean, to dip the ends of the wire into before dipping into the solder pot, and removing the dross as...
  12. hevans1944

    OpAmp oscillator circuit

    Also look at U2, which appears to be installed backwards: the supply, Vcc, is connected to the output, pin 3, while the oscillator/amplifier circuit is trying to draw power from the input terminal, pin 1, of U2. D3 also appears to be installed backwards if the intent is supply power from Vcc to...
  13. hevans1944

    Boxes

    Try looking on the web sites of electronics distributors. My favorites are Allied Electronics, Newark, and Digi-Key. There are others, such as Jameco Electronics, but the first three are my "go to" for quality components. Google is your friend.
  14. hevans1944

    Advice for Solar Charging Circuit

    Maxim makes an energy harvesting IC that may be appropriate: MAX17710. Unfortunately it has a maximum power input of 100 mW from a solar cell, and that is boosted to store energy in Infinite Power Solutions’ THINERGY® microenergy cells (MECs). This cell could then provide regulated power output...
  15. hevans1944

    Best solder to use

    Solder comes in a bewildering array of sizes and alloys. To learn more about it visit this Wikipedia page. For electronics use, I prefer a eutectic 63% Sn and 37% Pb alloy with a rosin flux core. My favorite is Kester 44, which is also available in SAC305 lead-free alloy, 96.5% Sn, 3.0% Ag...
  16. hevans1944

    APC Back-UPS XS1500

    This device contains a sealed lead-acid battery. After 3-4 years of non-use the battery will be dead. It may not accept a charge and, if so, will need to be replaced. You should download a copy of the user manual from this web site for troubleshooting if you haven't done so already..
  17. hevans1944

    Help selecting an alternative chip

    You might try using a quad SPDT analog switch.
  18. hevans1944

    soldering capacitors to board

    Yep. Cold solder joints fer shure. Cut the excess leads off, leaving about a 1/4-inch protruding above the copper side of the board. This will reduce the effect of the leads absorbing heat from the soldering iron. Re-heat each joint and remove the solder with a solder sucker or de-soldering...
  19. hevans1944

    Old RS-232 compatibility with new computers?

    I have several end-user devices that depend on a USB-to-serial device, usually part of a cable powered from the USB connection. The first one I encountered was an Elecraft KXUSB cable that is used to upload firmware updates to my KX3 transceiver and, later, to my KXPA100 linear amplifier that is...
  20. hevans1944

    Old RS-232 compatibility with new computers?

    It may not be your fault. You may have a problem with a counterfeit FTDI USB-to-serial converter chip. See this ZDNet article on automatic driver updates, distributed by Microsoft, that included FTDI driver software that checks for, and then bricks (makes inoperable) counterfeit FTDI chips. I...
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