Hardware Reference
In-Depth Information
On most breadboards you will find the two edge tracks that are connected down the length of the breadboard.
These are normally used as your voltage source and your ground tracks. You can then see that the breadboard is
divided into two equal halves. No current can flow across the divider strip in the middle of the board. The holes in
these sections are connected across the width of the board, but only in their set section. Other breadboards may
have different configurations. If you are ever unsure of how the holes are connected you can use the following simple
method to check.
1.
Place a jumper wire in one of the holes and then place another jumper wire into the next hole.
2.
Run a continuity check on your multimeter.
3.
Keep moving the second jumper wire around the adjacent holes to work out how the
breadboard is connected.
Once you know how the tracks on your breadboard flow, you can work out how best to place your components.
There are no hard rules about the placement of components. Just do your best to keep it neat and logical. This will
make it easier to debug if you need to. To insert wire or components into the breadboard, gently press their legs into
the hole: they won't go in too far and you will have things that stick out. Removing them is just as easy. Pull directly
upward and not at an angle to remove the components. If you pull them out at an angle you may bend the legs. If
they seem hard to remove, use a little flat-bladed screwdriver to lever each side up gently. I find that some integrated
circuits (ICs)s tend to be hard to remove and you often need to gently lever them up.
Sensors
I will be using two different sensors. Each sensor will be connected in different ways to the Raspberry Pi, so that I can
show you how flexible the Raspberry Pi really is. Let's start with the sensors.
Introducing the DHT11
Although I do have a strong preference for which sensor is better when connected to the Raspberry Pi, I'll start off by
talking about each sensor and why I like a certain type. First up I will talk about the DHT11. The DHT11 is an
eight-bit restive-type temperature and humidity sensor in one small package. The eight-bit value refers to the
temperature restitution. These will come in many different colors and appearances: it's a very generic part made in
China. They are easy to find and very cheap.
Sensitivity-wise, they are not too bad. The temperature range is 0 to 50
°C
and humidity is 20% relative humidity
to 90% relative humidity. Given that Hong Kong is often above 90% relative humidity it's not the best choice for me.
The good thing about the DHT11 is that it is in such a small package you can sense both temperature and humidity.
It also has a low pin count. You will most often see the DHT11 shipped with four pins although you only need three.
You can see the pins in Table
3-1
.
Table 3-1.
The pins for the DHT11
Pin Number
Function
1
Voltage Drain To Drain or Vdd (3-5 V dc)
2
Data (proprietary digital signal)
3
No connect
4
Ground
