• The Simplest Oscillator

Mike Szczys06/08/2015 at 23:18 0 comments

Making sound with a single logic chip is really quite easy. Let's take a look at the most basic sound producing circuit we cover in our serise. The full details of this are covered in the first installment of Logic Noise, but here we're going to boil it down even further. You need:

• 40106 Inverter Chip
• 2x 0.1uF capacitors
• 2x 100k potentiometer
• 1x 100k resistor
• 1x 10k resistor
• 9v battery
• powered speakers, like computer speakers
• Some way to connect everything together (a breadboard and jumper wires)

Here is a connection illustration:

When connecting your computer speakers you will also need a connection to ground (the blue lines in the diagram).

The heart of the circuit is shown below. The circuit makes sound using a concept called Hysteresis. This is a type of delay found in some integrated circuits. The 40106 chip we're using has a time delay between producing a low signal and a high signal; this is an oscillator. This change from low to high is at a frequency that produces a note. The protentiometer can change this frequency, making the sound higher or lower.

• Brainstorming / Architecture

Elliot Williams05/27/2015 at 21:59 0 comments

To make a permanent system from the Logic Noise potpourri, there's a ton of choices that need to be made. Here's a record of what I've been thinking.

• Chips: Clearly, we'll need at least one of each chip that's been featured in the Logic Noise series so far. That is to say: 40106, 4051, 4040, 4015, 4017, 4070, and a 4069UB.
• Hard-wired and convenient vs Flexible: This is the crux of the biscuit: what separates a Moog Modular from a Minimoog. So far we've been doing everything on a breadboard, which is the extreme of flexibility, but suffers for convenience. I'd like to be making simple sounds with three or four patch cords, and sequenced things with five or six. Not patch-cable spaghetti, but flexible.
• Special Functions: Flexibility is great, but re-wiring up the cymbal or bass drum circuit every time would be silly. Some things will just have to be hard-wired modules. We use a few 40106 oscillators every time -- they should just work out of the box.
• Connectors: Ideally, we'd all be rich, have huge workspaces, and the every input/output would have a well-labelled banana jack. With eight chips and 10-12 pins per chip, assuming 1in^2 and \$0.50 per jack, that's something like 200 in^2 and \$100 just in connectors for the whole system. That won't do. The compromise is to break everything out on male pin-headers and use female-female "Dupont" wires as patch cables. It's cheap, small, and easily compatible with breadboards.
• Multiples: Many connections to the chips will need to be doubled or tripled. Example: you'll want a tempo oscillator that can feed multiple clocks. I'll put two or three outputs where necessary and make up the rest with a few well-placed multiples.
• Power: Easy. 9V battery. Small, cheap, convenient. Works with rechargeables if necessary.
• Overall flow: Oscillators -> clocks / switches -> special modules -> output mixer. Not that it needs to be hardwired, but that keeping the order in mind will help layout.
• Audio Out: Ideally, headphone and line out jack. In practice, it's easy to do the line out correctly, but headphones really want a dedicated driver/amplifier and their specs are all over the map. So we'll fudge and do something with the 4069UB chip that'll probably work for both. Wish I had space for a speaker, but anything plausible will have crappy bass response anyway.
• Fine points: Inputs/outputs in the same order as on the chips, or grouped into logical sets, or grouped and ordered. Since space for writing legends is going to be tight, I think re-organizing stuff to make as much intrinsic sense is the only way to go.
• Luxuries: It's nice to have some LEDs around to help debug. A few tie points to VCC and GND never hurt. Pulldown resistors on all the sensitive inputs?
• Art / labels: It'd be nice to describe all the chips on the board artwork. OTOH, we're going to be cramped for space. Sexy artwork for the back side is a must.