Before we can solder together the Brain Board together, we need to identify which components go where. For this lesson, we will identify each component and what they do.
We will also make notice of what each component’s schematic symbol is. Components sometimes have several ways that they may be identified in a schematic drawing. There are symbols that are specific to certain countries like the USA or UK, as well as internationally accepted symbols. This lesson is not an in-depth lesson on how to read schematics, but rather will cover enough so you can read the Brain Board Schematic.
A nice tutorial on reading schematics can be found here: https://learn.sparkfun.com/tutorials/how-to-read-a-schematic/schematic-symbols-part-1
Open up your kit and take an inventory of the components.
You should have:
- (1) Brain Board PCB
- (2) 22 ohm resistors
- (1) 330 ohm resistor
- (1) 1k5 ohm resistor
- (2) ZD3V6 diodes
- (1) 1N4001 Diode
- (1) LED
- (1) USB Plug
- (1) Switch
- (1) Battery clip
- (1) Female Header
- (1) Light Emitter/Collector
- (1) 10uF Capacitor
- (1) 0.1 uF Capacitor
- (1) ATTiny Chip Socket (in silver anti static pouch — do not remove until ready to use)
- (1) ATTiny Chip (in silver anti static pouch — do not remove until ready to use)
Lay out the components in the relative position they would be laid out on the board. This will help us identify the components correctly. Later when we solder them to the board, we can make sure we are picking up the right components.
Resistors restrict the flow of electric current and how much they restrict is designated in Ohms. Ohms can also be represented with a Ω or Omega symbol. 330Ω is the same as writing 330 Ohms.
On a circuit diagram, resistors can be represented with a zig-zag line like in our illustration, or with a rectangle and their value.
Resistors don’t have polarity. There is no specific right to left (or up and down) orientation. In other words, the metal leads at either end can go into our board in either direction. This is not the case with LEDs as you had encountered soldering Buzz’s or Chip’s eyes.
If you look closely at your resistors, you will see a color code. Those colors represent the value of the resistor. Click here for a tutorial on how to read the color codes of a resistor.
1K5 is shorthand for 1500. 1K5 Ohm Resistor = Brown – Green – Red
330 Ohm Resistor = Orange – Orange – Brown
22 Ohm Resistor = Red – Red – Black
- 1k5 ohm resistor
- a 330 ohm resistor
- two 22 ohm resistors
They do have specific values in ohms that have to match the circuit specifications.
Note: The gold band is how accurate or how tolerant is this resistor. Gold = 5% tolerance on 330 Ohms.
If you are like me, reading the color codes can be difficult. Here are two suggested alternative to help you.
Method 1 (Visual Enlargement): Use magnifying glass or a smartphone to zoom in for a better view of the colors bands.
Method 2 (Voltmeter/multimeter): If you have a multimeter or voltmeter, it is a sure fire method way to measure the resistance across the resistor. If you have never used a voltmeter before, here is an excellent tutorial on how to use your voltmeter.
Turn your voltmeter to Ω and the 2000 range. When you measure the resistor, you will get an approximate value that close to what the designation of the resistor is.
Remember: we mentioned the Gold band is tolerance and a resistor can be + or – a percentage from it’s designated value
Diodes allow current flow in only one direction. They have polarity. It matters which way we place the diode.
We also have three diodes in our kit:
Zener diodes allow current to flow in one direction, but only after reaching a threshold of a certain voltage (their Zener Voltage), they will allow current to flow in an opposite direction. Evil Mad Scientist has an excellent explanation of how Zener Diodes work.
You may have noticed that the symbol for a Diode is the same as for an LED (which is shown later in this lesson). A LED is a one kind of diode. The Zener Diode is similar but has two wiggle lines.
For more in-depth information on diodes: visit Wikipedia at https://en.wikipedia.org/wiki/Diode
Capacitors store electrical charges similar to how a rechargeable battery works. When connected to a DC current, the capacitor will energize and store a charge and then can release its charge when needed.
Our Brain Board has two capacitors: a 0.1 uF capacitor and 10uF capacitor.
The 0.1μF Capacitor is a disc capacitor and does not have polarity and can go into the Brain Board in either direction.
Capacitance is the amount of electric charge that is stored in a capacitor at 1 Volt. The capacitance is measured in units of Farad (F) named for Michael Faraday. 1,000,000μF = 1F andμF stands for microfarads.
The 10μF we are using is the larger, round, capacitor and is known as a radial capacitor. The radial capacitor does have a polarity and has to go in the board in a specific direction. You will notice one leg of the capacitor is longer, this is the positive (+) leg. The shorter leg is the negative (-) leg.
You can learn more about capacitors here: http://makezine.com/2013/07/01/component-of-the-month-the-capacitor/
An LED (Light Emitting Diode) is a diode that emits light when a current flows through it. As with the diodes we saw earlier, a LED has polarity and must be in the right orientation in order to light up. You can also see that it’s symbol is almost identical to a regular Diode symbol except for the two arrows radiating outward.
The 5mm LED on the Brain Board is there to let us know that we have power via a USB connection. It will not light if we use the battery.
A switch is a mechanism that let us control the current flow. The Brain Board switch controls the power when the board is on battery, but not on USB power.
You will need to clip the three outer leads (It will be explained in the soldering instructions). To save space on the board, we placed the switch at the edge and before we solder the switch we need to clip those leads.
We have another component that looks similar to an LED, it is an Infrared (IR) Emitter Collector. It is an LED, but a very special one that can not only emit light in the infrared spectrum (like what is in your TV remote) but it can also receive infrared light.
The longer leg is the Emitter and the Shorter leg is the Collector. On the Brain Board PCB, the polarity for this component is designated with an E for emitter and a C for collector.
In the future, we will be able to use this component to have Pi Pals communicate with each other or do projects that include light sensing.
To connect the Brain Board to your computer, we do this via USB. The USB connector we will solder is a USB Type B connector. USB has four pins plus a the shielded connector (the exterior). Pin 1 is our 5volts, Pin 2
|4||ID||Mode Detect. May be N/C, GND or used as an attached device presence indicator (usually shorted to GND with resistor)|
The IC socket has 8 pins for the ATTiny85 chip that we are using. The ATTiny chips are delicate and can easily be damaged if we solder it directly to the PCB. However, the socket allows us to not solder the chip to the PCB and be able to replace the chip if we ever needed to.
ICs can be so varied that they do not have a special symbol, instead they use a rectangle with lines to denote the pins. IC sockets may not be denoted at all in a circuit diagram.
When you place the IC Socket on the PCB board, make sure the indent, or half-circle in the center top matches the orientation of the silkscreen on the PCB. This indent is the top and help us later orient the ATTiny so that pin 1 is in the correct spot.
The socket and the ATTiny for the Brain Board are packed in their own silver, anti-stat, bag.
The battery clip holds the 2032 Battery to our PCB board. There is not a symbol for the battery clip, but rather for the battery. On the PCB, there is the negative (-) pad for the battery, the positive (+) side of the battery that help us identify how to place the battery.
The female header is where we connect our Pi Pal, Buzz, to the Brain Board. The Brain Board uses a 10-Pin header that matches the same 10-pin header on an Arduino.
Similar to an IC, the schematic will only show a rectangle an the pinouts. The header has no polarity, but when you plug in Buzz, he should face forward towards the two “feet” on the Brain Board. The table below is a reference for the header pinout.
|1||Touch||D2 / A1||Connected to the touch sensor on the PCB.|
|2||Sound||D0 / PWM||Buzz’s Buzzer|
|3||Right Eye||D1 / PWM||Pi Pal Right Eye LED|
|4||Left Eye||D4 / A2||Pi Pal Left Eye LED.|
|5||Light Detect||D5 / A0||IR Collector Emitter on PCB|
|8||Batt +||–||Connected to Battery – 3V (+)|
It is the brains of the board. It is inserted into the the IC socket once everything has been soldered. Note the dot in the upper corner, this tells us where pin 1 is. The chip will only work if it is inserted in this way.
While the ATTiny is a pretty durable chip, do not play with it while it is out of it’s static control bag and not in the board yet. Excessive static can harm the chip.
The ATTiny is a Integrated Circuit from Atmel Corporation and is specifically a AVR ATTiny85-20PU. According to it’s datasheet, “The ATTiny25/45/85 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC architecture. By executing powerful instructions in a single clock cycle, the ATTiny25/45/85 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to optimize power consumption versus processing speed.”
Now, let’s start soldering the Brain Board!