All that theory is fun and all, but how about some actual hands on? I’ll try to create as many labs as possible, because in the end we want to build stuff.
This lab will start with some introduction to vital lab equipment. Without this equipment you will not be able to perform most labs. For the equipment I’ll introduce a low-cost and a recommended option. If you are serious in learning and working with electronics I highly recommend getting the recommended equipment. If you are unsure, go with the low-cost option.
The breadboard
A breadboard is a platform very suitable for rapid prototyping of non-critical systems. The breadboard is low cost and come in a lot of different sizes. All small example is shown in picture below.
A breadboard consists of a lot of rows in the center of the board, in which we can place components. A row usually consists of 5 holes and these 5 holes are connected together. This allows us to connect various components together. Alongside the rows we have one or two columns which are also connected.
In the image above the connections are shown. All the holes under the blue line are connected together. The holes underneath the red line are also connected. Note, the red and blue lines are not connected. The same is true for the rows underneath the green and yellow lines. Those holes are connected in groups, but the lines are not connected to one another (also two green lines are not connected, this is just to show you some of the connected lines).
For the labs I recommend to buy a so called 1260 breadboard or larger. The number indicates the number of holes. Smaller boards are possible, but you will quickly run out of room when constructing larger circuits. The extra space is really valuable. If you have the budget get a board with banan plugs. That really helps when you also buy a lab power supply.
Multimeter
Multimeters are available in all price ranges. From very high end meters to low cost meters. For the low voltage DC sytems we will be starting with a simple meter will be sufficient. The meters has to have to following functions:
- DC voltage measurement
- DC current measurement
- resistance measurement
Optional features that are nice to have are:
- AC voltage/current measurement
- Continuity check
- Diode measurement
Note: never use loss cost meters for high voltage/power applications, the low cost meters lack the safety features that protect you in case of an error or fault. If you are working with voltages above 120VDC or 50VAC, or powers above 50W get a proper tool. Your life is always more valuable than the cost of any meter!
For most of the labs a multimeter like the UNI-T UT133A is perfect. It is low cost, high ease of use and al the features required for most labs. Any multimeter with similar features will do as well.
Power supply
For the power supply there are also a legion of options available. The most flexible is a setup with lab power supplies. These are powered by mains voltage, have 1 or multiple outputs and come in a wide range of current ranges. If you want to buy a really nice power supply, get one with two independent outputs at least 0-20V of voltage range and 0-2A or more in current range. For the first labs a single power power supply will work, but for later labs a dual power supply is the best.
The resistor
The resistor is one of the most commonly used components in electronics. They come in various shapes and sizes, from very tiny 01005 resistors to massive power resistors capable of dissipating kilo watts of power. We are for the moment mainly interested in standard 0.25W through hole resistors.
Through hole resistor come with a color coding. The color coding indicates the value and the tolerance of the resistor. The table below shows how to decode a resistor value.
| 1st ring color | 2nd ring color | 3rd ring color (multiplier) | 4th ring color (tolerance) | |
|---|---|---|---|---|
| Black | 0 | 0 | 1 | |
| Brown | 1 | 1 | 10 | 1% |
| Red | 2 | 2 | 100 | 2% |
| Orange | 3 | 3 | 1k | |
| Yellow | 4 | 4 | 10k | |
| Green | 5 | 5 | 100k | 0.5% |
| Blue | 6 | 6 | 1M | 0.25% |
| Violet | 7 | 7 | 10M | 0.1% |
| Grey | 8 | 8 | 100M | 0.05% |
| White | 9 | 9 | 1G | |
| Silver | 100m (0.1) | 10% | ||
| Gold | 10m (0.01) | 5% |
For example a resistor with a value of 1.2k and a 5% tolerance has a color code of: Brown, Red, Red, Gold To calculate this we first take the first number of the value 1, which is brown. The second number is 2 which is red. We now have the value 12. If we want to get to 1.2k we have to multiply this by 100, which is also red. Finally for the tolerance code we have to use the table.
The other way around also works. If we have a resistor with the color code Green Brown Yellow Gold we can calculate it’s value. Which is: 5 (green) and 1 (brown) so we have 51. This is multiplied by 10k (yellow) so we get 510k with a 5% (gold) tolerance.
Lab 1
We are going to build the following schematic as a real circuit.
$$R_1$$ = Black Black Red Gold $$R_2$$ = Red Red Brown Gold $$R_3$$ = Yellow Purple Brown Gold
Figure out yourself what the actual resistance values are.
When you finished building the circuit on the breadboard it should look something like this:
Multimeter setup for current measurement
For KCL we are going to do a lot of current measurements. So lets setup our multimeter to do some proper measurements.
Step 1 Setup probes
Step 2 Setup function
Now that you are setup, we can start measuring. At first measure the current flowing through $$R_2$$. To measure current we need to put the multimeter in series with a component. In series means 1 probe of the multimeter is connected to the one end of the component and nothing else, the other probe is connected the where the component was originally connected to. Is this confusing? May the next picture will help:
To measure the current in $$R_2$$ you remove the lead of the resistor that is connected to resistors $$R_1$$ and $$R_3$$. Now you connect one multimeter probe to the connection point of $$R_1$$ and $$R_3$$. The other probe is connected to the unconnected lead of $$R_2$$. If you did this correctly you end up with the following schematic representation:
The multimeter is placed in series with the component you want to measure. A component in series with another component means they only share 1 common connection and that common connection is only shared between the two components.
Now measure the currents of all other resistors and write them down. Carefully connect the probe leads of the multimeter to make sure to measure ok.
If you have done this correctly the sum of the currents $$I_{R2}$$ and $$I_{R3}$$ should be equal to $$I_{R1}$$. This is Kirchhoff current rule in practice!
If they did not add up to 0 there could be two things wrong here.
1. The tolerances on the resistors are just unlucky for you, and due to rounding to whole milli amps you got a wrong answer. Check you measurement with more digits (note, checking with more digits might results in the last digit being wrong as well, due to measurement errors).
2. You are switching the probe leads around. A multimeter presents a positive number if the current is flowing into the current measurement terminal, and out of the COM terminal. If the current flows in the opposite direction the multimeter will report a negative number. So to do it correctly always have the same side of the multimeter connected to a node. If you do this, all the measurements will add up to zero.
Lab 2
To become comfortable with current measurements and building circuits on a breadboard we need to get some mileage in. Build up the following circuit:
$$R_1 = 2.2k\Omega$$, $$R_2 = 470\Omega$$, $$R_3 =1k\Omega$$, $$R_4 = 330\Omega$$, $$R_5 = 220\Omega$$
Measure the currents in this circuit and check if Kirchhoff is valid in all nodes (the answers should match to within $$0.1$$mA.