Tuesday, March 19, 2013

Breadboard Basics 3: Multiple Examples of Schematic to Breadboards

We can consider this post somewhat of an addendum to Breadboard Basics 1 and Breadboard Basics 2. This post assumes that you have read both, or are familiar with the concepts.

Here are some basic examples of schematics and breadboard setups for 40106 oscillators. For more complex circuits, please see my Fun with Sea Moss page as well as Nic Collins excellent book, Handmade Electronic Music.

It's All About the Datasheets
This post revolves around the 40106 chip. We can find out more about this chip by finding what is called its "datasheet". A datasheet contains all relevant information to the physical, electrical and electronic characteristics of the chip.

Here is a datasheet for this chip. There's so much information there! Too much, actually.

Let's think about this and filter it down... in order to use this chip in a circuit from a functional point of view, we are actually only interested in four main things:
1) What is the functionality of this chip? 
2) Which voltage range can we use to power this chip?
3) What is the pinout of this chip?
4) What is the function of each pin?

So, where in the datasheet can we find this info? Well, we can usually find points 1 and 2 in the general description of the chip. Datasheets from different manufacturers might look different, but in general they have a one or two paragraph description of the chip and what it does.

For example, the general description of the chip from this datasheet is as follows:

"The HEF40106B provides six inverting buffers. Each input has a Schmitt trigger circuit. The inverting buffer switches at differentpoints for positive-going and negative-going signals. 

The difference between the positive voltage (VT+) and the negative voltage (VT-) is defined as hysteresis voltage (VH). The HEF40106B may be used for enhanced noise immunity or to “square up” slowly changing waveforms. 

It operates over a recommended VDD power supply range of 3 V to 15 V referenced to VSS
(usually ground).

Straight away, we know that we are dealing with a chip that inverts signal using up to six inverter stages and requires a voltage range of 3V to 15V, meaning that we can use a range of power supplies like: 2 x AA, USB, 4 x AA rechargeable or a single 9V battery to power this chip. This covers points 1 and 2 quite well.

In order to find points 3 and 4 from above, we need to scroll down through the datasheet. There, we can see a physical layout of the chip as well as a functional layout of the chip.

Let's examine the physical layout of the chip:
We have a standard 14-pin chip, where the numbering is standard - moving in an anti-clockwise direction from the left of the half-indent.

Functionally, it seems obvious from the general description as to what VDD and VSS are - they should be connected to the positive (VDD) and negative / ground (VSS) terminals of our power supply.

But.. what are all of these pins marked A and Y? What function do they perform? Well, we need to consult the functional diagram, as below:
The functional diagram does not physically represent the chip -  note the chip leg numbers on the outside of the rectangle, and compare them to the physical pin layout!

Here, we can see that the 'A' pin represents the INPUT part of an inverter, whilst the 'Y' pin represents the output side of an inverter. We have six inverters in total. A datasheet will often times also include a description of the function of each pin as well, which can be handy if the diagrams seem confusing.

Now, with that information in mind, we can go ahead and go from a schematic to a breadboard using chips we don't fully know or understand, as long as we can extract the relevant information from the datasheet.

Schematics and Breadboards
In order to use this chip in a circuit, we need to consider 1) power supply and 2) output. Here are a set of schematics and breadboard layouts that use 1) a 9V battery and 2) a piezo transducer. Naturally, a range of options can be used to substitute either.

RC 40106 oscillator with fixed frequency - with piezo output

• Try changing the resistor. What do you notice?
• Try changing the capacitor. What do you notice?

RC 40106 oscillator with variable frequency - potentiometer version - with piezo output

• Try adding a resistor in series with the potentiometer. What do you notice?
• Try using a 1MΩ potentiometer in series with a 100kΩ potentiometer. What do you notice? 

RC 40106 oscillator with variable frequency - LDR version - with piezo output

Sometimes, schematics only provide the very barebones of what we need to know about a circuit in order to build it.

It is very handy to have a datasheet about the chip or component of a particular circuit, so that we can double check the pinouts of that chip when we are making a breadboard version of the circuit.

Schematics might not include power supply connections, so we need to add these in as well as output destinations for our signal. In order to add our power supplies, we need to know more about the chips: Which pins require power? How much voltage?

All of these steps are necessary in order to build functional breadboard circuits.