Byron J.

Member Since: September 10, 2013

Country: United States


Apparently, the J is for JFET.

Thoughts and ramblings about numbers, plus an interesting discovery.

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Examining one of the categories that occupies significant space on my workbench: wire strippers.

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Drive the Moog Werkstatt-01 with the SparkPunk sequencer, and starting in on a MIDI-to-CV converter.

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Experimenting with optics and imagery.

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Pi Wedge B+ Hookup Guide

December 18, 2014

How to assemble and start using the Pi Wedge to prototype with the Raspberry Pi B+.

Decade Resistance Box Hookup Guide

December 4, 2014

How to assemble the decade resistance box, then use it as a design and measurement tool.

SparkPunk Sequencer Theory and Applications Guide

August 14, 2014

Examine the inner workings of the SparkPunk Sequencer, then explore some modifications and alternate applications.

SparkPunk Sequencer Hookup Guide

August 14, 2014

How to assemble and use the SparkPunk Sequencer kit.

SparkPunk Hookup Guide

June 12, 2014

How to assemble and modify the SparkPunk Sound Generator kit.

Pi Wedge Hookup Guide

May 29, 2014

How to assemble and start using the Pi Wedge to prototype with a Raspberry Pi.

Sound Detector Hookup Guide

February 27, 2014

The Sound Detector is a microphone with a binary output. This guide explains how it works and how you can use it in your projects.

Large Solderable Breadboard Hookup Guide

February 27, 2014

This breadboard has a couple of tricks up it's sleeve!

VKey Voltage Keypad Hookup Guide

February 13, 2014

A quick hookup for the VKey analog voltage keypad.
  • I knew I shoulda just said “DEC!”

  • These tests are actually pretty cumbersome to implement in code, since you’ve have to convert numbers to strings, then cycle through the strings to compose the sums. Unless you’re working in COBOL, where numbers are intrinsically strings, it’s not terribly efficient.

    Where it is efficient is in the programer’s brain while designing and debugging software. If you need to recognize particular multiples, it’s easier if you can just “see” them, than to have to pull out a calculator.

    The thing it does help with is that you can occur in the programmer’s noggin

  • Yup - you’re right. Now fixed.

    I cloned & mutated the decimal figure to make the hex. I remembered to change all the numbers, but forgot the text.

  • At this point, you’re in deeper than I am - that project was pretty hastily tossed together. Your theory seems correct, for the most part.

    It could be that I miscopied resistor values (33K for 3.3k?), and compensated with an additional resistor.

    So with 33K, I overshoot on Vref - we can’t reach 20V on a 13V supply, so it’s probably nearer 13V, but still really high in comparison to the Sound Detector output.

    The trick comes in that 100K - The Rhi pin isn’t HiZ, but rather the top end of the internal resistor ladder for the comparator chain. Page 17 of the LM3916 datasheet indicates the chain adds up to 10K. So it looks like I really overshot on the reference voltage (by about a factor of 10), then put a 100K resistor at the top of the ladder to scale it back down (by a factor of about 0.1).

    Maybe if I hadn’t botched the Vout, it would have been happier on a lower supply…I’ll leave that exercise for the reader.

  • I think I initially followed the same line of thinking - power everything off the same, low voltage power supply.

    Powered off 5V, the LM3916 was misbehaving, as I remember. Some segments wouldn’t go out, or it was in some flaky halfway state between dot & bar modes. Switching it to the 13V supply solved it, and I didn’t dig much deeper.

    At this point, I don’t recall why it was 13V, or if there’s any specific magic to that value. 9V might be fine.

    The op amp at the heart of the sound detector is the first constraint against higher voltages. The LMV324 is rated to an absolute maximum of a 6V supply. A 5V supply leaves some margin for error.

    If you’re designing your own board, you could use an LM324, which is pin compatible rated to 36V max. You’ll also want to use caps rated to higher voltages.

    Alternately, there are also smaller regulators - the 78L05 is the little brother of the 7805 in a TO92 package, there’s also an LM317L.

  • There’s certainly an aspect of this that boils down to understanding what your tools are capable of, and having a gut feeling of when they’re telling you something unreasonable. There’s a chance that your meter just reads 1.5mV, even when the actual input is less than that. A millivolt is pretty tiny.

    If you want a really readable guide to using meters and scopes, and knowing when to suspect the results they yield, Bob Pease’s Troubleshooting Analog Circuits book is great. Pease is extremely knowledgable about electronics, and also a good (if opinionated) writer.

    I wasn’t able to stabilize that bench supply by throwing caps at it - trust me, I tried, and eventually gave up, opting for the LM317 solution (with appropriate caps on I and O pins).

    Have you tested the Sound Detector with any of the batteries or supplies you mention? At the end of the day, the proof is in the results. As mentioned in the tutorial, 0.000 VAC is an ideal goal - perhaps somewhat hard to attain. 10 mV seemd to be the threshold above which they detector got twitchy.

  • There are several pieces this discussion - I’ll step through each in turn.

    The first is the measurement method - when you’ve got the measurements leads just floating in the air, they’re antennas, and they’ll pick up interference from all over the place, including AC radiated from power lines. With my scope and meter leads just dangling, I read about 15 mVp-p on the scope, and 43mV on the meter. If I grab the wires, I get much higher pickup.

    For reference, the scope is a Tek TDS2024 with 200MHz/10MΩ probes - the meter is a Fluke 115. The VAC range on the Fluke is only specified up to 1KHz - if I’ve got high-frequency noise on the supply, it won’t register - but the scope will show it clearly.

    If I short the leads together (red-to-black with the meter, clipping the alligator on the scope probe right to the tip), the high-impedance antennas just become wire loops, and the noise is greatly reduced. The scope input is still noisy - even with no probe connected, I get 10mV or so - but the meter registers no voltage - 0.000 VAC.

    A good neutral reference isn’t with the leads floating, but with the inputs shunted to ground. If your meter doesn’t read 0 VAC with the inputs shorted, it may indicate that the meter has some internal issues. Many meters are designed to be useful working on household wiring - millivolts AC may not be it’s primary selling point. Many scopes have a switch or option to short the input to ground for verification purposes.

    So to start, you need to characterize the test equipment a bit - I know that my scope is noisier than my meter, therefore I use the meter to make small VAC measurements, within it’s frequency limits.

    Moving on, and using said meter to measure AV noise from some different supplies on my bench (and verifying their sanity within the abilties of my scope), here’s what I see:

    • Generic 9V battery: 9.53 VDC, 0.000 VAC
    • Rayovac 9V battery: 8.59 VDC, 0.000 VAC
    • 12V Wallwart: 12.2VDC - the meter reads 0.000VAC, but the scope shows narrow 100mV spikes at about 1KHz.
    • Cheap bench supply:
    • Results vary with the setting and load - it’s very clean at 9V, unloaded. At 5V, unloaded, it’s making a 70mVp-p sawtooth - add a 16Ω power resistor, and the frequency of the saw goes up.

    It’s this cheap bench supply specifically that I wanted to account for in the hookup guide. For powering a small microcontroller, the bench supply is fine. But it makes the sound detector unusable - the noise on the supply is coupled into the microphone output, and the Schmitt trigger wiggles around, also, making it almost impossible to set the sensitivity to anything useful…the light just flickers, regardless of ambient sound.

    If nothing else, it’s worth testing with the noisy supply, so you can see the difference when you move to a more stable one. The difference is immediately obvious.

    So how to handle it? I used an external voltage regulator to clean it up. The demo board I’ve got handy used a LM317, strapped for 5V. It gets the noisy ~10 V input from the bench supply, and scales it down to a clean 5V. LM78xx regulators are also useful - LDO and switching regulators might work, but I haven’t characterized them in this application.

  • Radio Shack was also a notable “stencil brad” carrier. some of the electronics products were built by other vendors, and dressed up with an in-house trademark, like Optimus or Realistic.

    I’ve got a Realistic MG-1 synthesizer that’s a Moog under the hood…the brother of the Moog Rogue, minus the pitch bend wheel. Back before the internet was really a thing, and schematics weren’t easily available, I was able to order the service manual for that MG-1 from the Shack. It was a $12 or $15 well spent - complete schematics, theory of operation and test/calibration procedures.

    Also interesting to note that after all these years, the guts of the Moog Werkstatt aren’t all that different from the MG-1, and they’ve released the schematic for it - this time for free!

  • If you’re looking at the jack from the panel-mount end (the side with the threads and nut), and the legs are pointing downwards, it goes like this:

    The right hand set of pins are the connections.

    • the closest to the panel is the sleeve.
    • the next pin is the ring
    • the furthest from the panel is the tip.

    The left set of pins are the normals, in the same order: sleeve nearest the panel, then ring, then tip.

    When no plug is inserted, the each normal ties to it’s corresponding connection (Tip->tip normal, ring->ring normal, sleeve->sleeve normal). When the plug is inserted, these connections are broken. The connections are then tied to the signals in the jack, and the normals are left floating.

  • At this point, we’ve also got a wedge for the B+!.

    But as luck has it that they’re backordered at the moment, so the stacking header plan might be called for anyways.