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  1. AnalogKid

    12v bipolar square wave oscillator

    On this datasheet: http://www.ti.com/lit/ds/symlink/tl072.pdf figures 15 and 18, the output performance into 2K is significantly worse than the specs at 10K. Your load is 1.2K at the beginning of each cycle, even worse. Can you post a scope shot of the TL072 output? Then, increase R 10x and...
  2. AnalogKid

    12v bipolar square wave oscillator

    Schematic? ? ? A 0-12 V square wave through a suitable coupling capacitor will center up nicely around GND. +/-10 mV out of 6 V is 0.16%. No way will you get that kind of accuracy relying on the saturated output voltage of either opamps of 555s. What kind of circuit does the output drive...
  3. AnalogKid

    Building a two digit counter

    Separate from that, what about the hold-at-21 function? It was a requirement in post #1 (and the single most difficult part of this project), but not in post #4. If it is not a requirement then any counting display module will work, and there are hundreds of them on ebay...
  4. AnalogKid

    Building a two digit counter

    My view of this is this - Assemble and solder all of the parts on board #1. Connect wires to the power source and switches. On board #2, assemble and solder the displays, display resistors, IC2, IC3, R6, R7, C1. This gets you the displays, their current limiting resistors, their drivers...
  5. AnalogKid

    Building a two digit counter

    When you connected the displays in parallel, I assume you had only one set of resistors and connected the diodes in parallel. As you have seen, 2 LEDs in direct parallel don't work well. The forward voltages are not perfectly matched, so the one with the lower forward voltage gets most of the...
  6. AnalogKid

    What type of wire is copper wrapped around fluffy threads?

    https://en.wikipedia.org/wiki/Litz_wire It is used in ear buds because it is super flexible without breaking. ak
  7. AnalogKid

    Bypassing TV's internal speakers to home-made aux input

    There is no IF here. The two big yellow things on the right side pc board with writing on them are power transformers. Note that the cross-hatched marking (the isolation barrier) runs right underneath them between the primary and secondary pins. Drive to the speakers is almost certainly...
  8. AnalogKid

    T8 - LED shop lighting

    I've been wondering about this. My basement has 36 tubes (9 light pans x 4 per pan). Years ago the company got a tax break by replacing all of the inductive ballasts with solid state and all of the 40 W bulbs with 34 W. I cherry picked three cases of lightly used tubes. Now I'm down to the...
  9. AnalogKid

    AC to AC relay for Landscape Lights

    Since response time is not critical (post #3), why not just one diode? That plus 100 uF would yield a turn off time of about 0.1 s for 10 mA SSR input current. ak
  10. AnalogKid

    AC to AC relay for Landscape Lights

    R02−11A10−6 looks like it meets your requirements it you can get it 6 Vac. Why does you AC source vary over such a wide range? A hockey puck SSR should be around $5 surplus, $21 new at Digi-Key...
  11. AnalogKid

    AC to AC relay for Landscape Lights

    What is the source of the 3-9 Vac? How much current at 120 Vac does the relay need to switch? How fast does the relay need to turn off after the 3-9 Vac goes away? The low voltage AC source current or power sets a limit on what relay coils are possible candidates. The AC load current gives us a...
  12. AnalogKid

    Not sure to be safe or sorry

    And even if the supply you are using is set to only 3.3 V, *always* have a resistor in series with the LED you are testing. Some LEDs have current limiting built in internally, but ... "be safe or sorry" ak
  13. AnalogKid

    Power supply series connection

    If you want the full output of 150 W, you will need power supplies that can deliver 4.5 A minimum, and preferably more like 6 A each. But with 1 A supplies you can determine if the rest of your circuits work correctly and get some volume. for what you have now, something in the 1N5401 - 1N5404...
  14. AnalogKid

    Not sure to be safe or sorry

    Schematic? It sounds like the LEDs are in direct parallel. This will not work well, as the individual forward voltages are not matched and do not track, so some will be brighter and hog all the current. A better way is to have a current limiting resistor for each LED A way to save battery...
  15. AnalogKid

    Power supply series connection

    Every time the supplies are powered up, one of might reach its output voltage before the other one is powered up and stable with a low output impedance. Whichever one comes up first will appear as a reverse voltage on the output of the slower one, through the load. Depending on how much...
  16. AnalogKid

    Circuit schematic

    Internally, this probably is a single-chip design, with the chip either a custom-programmed uC or a fully custom part that integrated the wireless controller into the keyboard scanner. IOW, there might be no signal trace spot to get the keyboard coding before it goes to the radio section.
  17. AnalogKid

    Morse code led without a micro controller

    Edit: U1A and U1B form the divide-by-three counter.
  18. AnalogKid

    Morse code led without a micro controller

    First pass. R1-C1 form the space timer, approx. 0.5 s. R2 adds in for a three-times longer dah mark time. R3 is paralleled with R2 for the shorter dit mark time, a few percent longer than the space time. U1A-D4-D5 form a divide-by-three circuit. U2A is a toggle ff that uses D6 to switch R3...
  19. AnalogKid

    Morse code led without a micro controller

    Close, but - The space between dahs is one dit. If a dit is 1 sec (for round numbers), the dit LED on time is 1 sec, the dah LED on time is 3 sec, and the LED off time is 1 sec for both dits and dahs. Tricky. Almost done with a counter schematic. It cheats because it has the space between...
  20. AnalogKid

    Bone conduction low frequency speaker

    True, but there is nothing in post #1 against that. ak
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