Sqquare Wave generator

Discussion in 'Homebrew and Kit Projects' started by WA9SVD, Mar 13, 2017.

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  1. WA9SVD

    WA9SVD Ham Member QRZ Page

    OK, I've checked my archives, and Googled a Googleplex of times with no results that seem to fit.

    Many years ago, I built a simple square wave generator, using a MC-799P Dual Buffer (anybody still remember RTL Logic???) One IC, two resistors, and two capacitors were all that was needed to run off two AA batteries for over a decade.. [Probably over four decades by now, but with occasional battery replacement every 20 years.:rolleyes:] Harmonics of the ≈1 kHz osc. would go well into the VHF TV range!
    I can't remember if the circuit was from Pop'Tronics or Radio Electronics, probably early 1970's. Does anyone have such mags in their archives that may have the original circuit?
     
  2. WA7PRC

    WA7PRC Premium Subscriber QRZ Page

  3. KE0ZU

    KE0ZU Ham Member QRZ Page

  4. WA9SVD

    WA9SVD Ham Member QRZ Page


    I'm more than aware of what the NE-555 and it's siblings can achieve. I'll '' look up the previous previous posts. But I want to document EVERYTHING in my shack, at least that which is still in use. (For that matter, I still use a digital clock for Field Day that I built in 1972, for my VW Beetle, and it still works...)
    I've had the small oscillator for centuries (or so it seems) and have it in a small Rat shack Shack enclosure, with banana posts on the back, a Variable output level control for BNC fixed or variable output, and even small (low level) speaker output on/off. It's been a real god-send in many cases as a signal generator or source. But I don't want to disassemble it to reverse(dis) engine-ed it. As I remember in the fogy daze of college, I made the PC board for it. And it STILL works, which is somewhat a miracle. (Silly me, I soldered the IC onto the PC board, and current prices for that IC are $ 7.85, so it would not e economical to try to repair; a newer design would be better, but I still would like to document the original circuit I used..
     
    Last edited: Mar 13, 2017
  5. WA0YDE

    WA0YDE Ham Member QRZ Page

    I can't help you with your original project, but if you want to build a new one check out the XR-2206 function generator chip from EXAR. It's been around for many years. GL
     
  6. WA9SVD

    WA9SVD Ham Member QRZ Page


    This was (and is) a "quick and dirty, pun intended) " signal generator It serves a basic function, and can even drive a small speaker at low, but usable volume.. I have an ICL 8038 board that generates square, sine, and triangular .wave signals, but I haven't decided on a proper buffer amp or case layout to finish the project. I just would like to have the original circuit for the one RTL IC oscillator for MY archives.
     
  7. WA7PRC

    WA7PRC Premium Subscriber QRZ Page

    A former coworker tasked me with producing a simple pulse generator with independently variable rate and duty cycle controls. I found the Intersil ICL8038 to produce a clean triangle waveform. I buffered/offset that to a 0-5V signal and passed it thru a comparator w/ 0-5VDC reference...
    [​IMG]
    (click for bigly image)

    I used a 74HC244 to give it yuuuge output current capability, and used one gate to drive seven others. The output can be gated. And because the ICL8038 (NTE864) also produces a nice sinewve, I brought that out as well. I packaged it in a box w/ the electronics mounted to a blank PCB:

    [​IMG]
    (click for bigly image)

    The current going price for a NTE864 substitute is $40-50 but, the original Intersil ICL8038 can be found on evilbay for a lot less, such as $0.96 each (link). And there are likely other alternatives. The IC needs +/- 12VDC, so I just used an off-the-shelf DC-DC converter module. Controls are 10K/10T pots w/ turns counter dials... probably the costliest parts but, they're worth it.
     
  8. WA9SVD

    WA9SVD Ham Member QRZ Page

    With all due respect, I do NOT want or need suggestions for a "new" signal generator. The project has been built and in use for over 40 years. I'm just looking for the ORIGINAL oscillator schematic that I used with the MC799P (RTL logic) IC, which has two different input options. YES, reverse engineering would allow that (since I made the PC board myself.) In my early daze, I (unfortunately) didn't document simple circuits completely. NO need to suggest using other circuits. PIX when I can get the camera batteries charged.
     
  9. VK4FFAB

    VK4FFAB XML Subscriber QRZ Page

    Pop the lid off and have a poke about in there with your peepers. Wont be hard to fabricobble a schematic from 5 parts. Its probably a circuit straight out the application notes. A library of motorola books might be useful here also.
     
  10. VK4FFAB

    VK4FFAB XML Subscriber QRZ Page

    Oh and it sounds like what you made is a Comb Generator, 1 of the MC799P buffers was used with 2 caps, 2 resistors and a xtal or ceramic resonator to form an oscillator and the other 3 buffers cascaded to give amplification. Probably something like this, being a comb generator the harmonics will have flat gain into the stratosphere.

    [​IMG]
     

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