Adrian Freed

Summary

Demonstrating an unusual application of a CMOS NOR gate to implement a CMOS varactor controlled VCO, I explore the idea of circuit schematics as a music notation and how scholars and practitioners might create and analyze notations as part of the rich web of interactions that constitute current music practice.

Summary

I introduce a new synthesizable VCO using (n+1) mux2i cells from the SkyWater130 PDK to form a (2n+1) hybrid ring oscillator.

Intro

I am studying how IC routing is done in large chips. I am following advice I often give people that it is helpful to learn how to do something by hand before using an automation tool. I was skeptical about this for chip routing because the scale of the problem these routers solve (trillions of gates) is outside what can be done by hand. As it turns out a few of the things I know about routing PCBs helped prepare me for learning some of the conceptual and strategic aspects of what these tools do.

This alternative to the 555 timer for making audio oscillators is built from simpler building blocks (inverters) and has more versatility. You can find the schematics that correspond to the build video here: https://www.youtube.com/watch?v=CzO_ZKMSnAU

In a recent workshop on e-textile sound for the 2018 e-Textile Spring Camp, I provided a unifying framework for analog and digital sound synthesis and capacitive sensing techniques under the rubric of relaxation oscillators.

The following pages provide context for the workshop and include links to contributions from my co-teacher, Martin De Bie. This includes pointers to various iterations of his 555 timer-based Textilo project.

This project will be expanded ongoingly with further relaxation oscillator schemes.

History

There are few inaccurate histories of the 555 timer invention on the web so a good source is from the designer himself, e.g., http://semiconductormuseum.com/Transistors/LectureHall/Camenzind/Camenzi...

He also wrote several interesting books. The history and detailed design considerations are covered in a book he kindly made available as a PDF file before his death in 2012: http://www.designinganalogchips.com/_count/designinganalogchips.pdf

Circuits

This is a reasonable compendium of interesting circuits using the IC: http://www.555-timer-circuits.com

Some more:

http://www.nutsvolts.com/magazine/article/using-the-555-timer-ic-in-spec...

Radio Circuits

AM Receiver

https://hackaday.com/2011/02/25/hear-that-its-a-555-timer-am-radio/

AM transmitter

http://www.circuitsgallery.com/2013/08/555-AM-transmitter-circuit.html

FM

http://streampowers.blogspot.com/2013/07/using-555-as-fm-transmitter-cir...

Audio Circuits

VCO

High Performance VCO : http://www.electro-music.com/forum/topic-54623.html DRAWDIO

https://www.adafruit.com/product/124

ATARI PUNK CONSOLE http://www.synthrotek.com/products/lo-fi-synthesizer-circuits/atari-punk...

Variations

The CMOS versions of the 555 timer are interesting and lend themselves well to low voltage e-textile applications. My favorite variant is this one: https://www.jameco.com/z/CSS555-ID-Custom-Silicon-Solutions-CSS555-Micro...

Here is the largest variant I know of: https://shop.evilmadscientist.com/productsmenu/tinykitlist/652-555kit

and the smallest (a 1mm x 1mm) package:

http://www.ti.com/product/LMC555/samplebuy https://www.mouser.com/Semiconductors/Integrated-Circuits-ICs/Clock-Time...

In the usual approach to PCB layout traces are laid out to connect signals and power to the pads of packaged parts and I/O connectors. This is a style that evolved for very high speed digital circuits. One usually also employs ground and/or power planes or a ground flood.

This style is not convenient for eTextile Appliqués which are most commonly single-sided and are based on cut traces rather than etched boards.

There is an older style of PCB layout that is more suitable for low-speed e-textiles that I remember seeing with old transistor radios. The style is almost all copper with just a few lines etched away to separate conductors.

This makes designs more robust with multiple parts soldered on and removed and with multiple sewing points at the edges.

It also makes for less weeding and more surface area that will be fused/glued to the base fabric.

It was also common for many of the traces in these radios to be curved.

For the eTextile Spring Break I guided Martin De Bie through some iterations of his original Textilo design that includes this new thinking on layout and a further insight regarding the 8-pin DIP packages commonly used now by eTextile electronics experiments (with the ATTINY and 555 timer being common choices). This insight is to start the design from the DIP package and imagine the negative space of the smallest amount of conductive fabric that needs to be weeded to separate the 8 pins and combine the constraint of roughly equal area given to the conductors attached to each pin. This results in a motif with 8 radial lines and 8 triangles between them.

Here is the original textilo with its elegant pads to sew to:

Here is the next version with more conductive material to work with alongside the prototype of a radial design. The radial design includes serpentine interdigitation to allow for touch interaction:

Nicole Yi Messier picked up on this radial design pattern for her wearable 555 timer based FM radio transmitter:

The entries in this table with an * were briefly reviewed in the 3 hour workshop the 2018 eTextile Spring camp. As the table shows, these are in the middle of the affordability/complexity/size axis and were selected for their potential in e-textile and wearable contexts. We had the good fortune to have Bela well represented in another workshop at the camp. Bela is transitioning to a new compact form factor which will make it easier to use with e-textiles.

I learned about this work as a teenager and managed to trace my fuzzy recollection while researching connections between textiles and electronics. It was published in Cybernetica Volume 2.

"I have recently completed building an electronic model of the 'growth net' principle and will now give a brief outline of its method of operation."

"What I described earlier as a common boundary now takes of the form of a moist fibre of cotton yarn connecting each input to the control grid of a pentode"

"The use of moist cotton fibre for storage has considerably reduced the size of the machine from the original plan which was to use condenser storage. By application of a hygroscopic agent such glycerin to the fibre the memory time of the machine can be controlled".

When I saw Martin De Bie's Textilo e-textile 555 oscillator I wondered if it could be extended to allow for body interactions with the pads using CMOS 555 timers in the spirit of the CrackleBox.

I tested this CMOS 555 breadboard version.

This informed suggested improvements to Textilo to Martin who came up with a textile layout which we used to teach during the audio workshop of e-textile Spring Break: http://youtube.com/HdMsk6c3WGw

Alex blogged a great student perspective of this workshop.

I also brought along some PCB's which can be sewed to or pressed on Lego baseboards.

To address the need for more interaction room for the fingers I suggested to Martin to look at a radiating octagonal design. He prototyped this at the camp in copper:

Nicole Messier also picked up on this design pattern and made a 555 oscillator based FM Radio transmitter:

A walk through the schematic may be helpful.

We install a capacitor to ground (470pF) from pin 2.

Pin 6 is connected to Pin 2.

A 1Mohm pullup resistor is used on pin 4 (reset).

There is a decoupling capacitor for the speaker output (pin 3)

The diode (from battery to pin 8) is to help you not destroy the 555 timer if you install the battery backwards.

Now what makes things productively confusing is the absence of resistors in the story. These are provided by your fingers or additional LDRs or piezoresistive fabrics. The layout is designed to give you room to put fingers in the useful places for the two popular ways of making the 555 timer oscillator. One way creates square waves. The other makes controllable pulse waves. I capture these possibilities on the following schematic which has a special notation for where you add variable resistance: