Generally, how are capacitors picked? (Applies to radio, MCU's, digital, analog)

Hi Thomas,

They store a certain amount of charge when you stick a voltage across them, but that is much like describing a glass window as "made of silicon dioxide", which while true at a high level, doesn't explain glass nor windows in much detail.

In electronics, there are certain fundamental circuits that can be created using capacitors; these fundamental building-blocks become parts of larger circuits like computers, radios, etc.

Here are some building blocks which can all be created with capacitors and other components:

1. Decoupling

2. Filter

3. DC blocking (related to filter)

4. Tank circuit

5. Timing (often used for resets)

A computer will make extremely extensive use of the first block and #5, whereas a radio will make use of #1,2,4 and an amplifier will make use of #1,2,3.

There are formulas which are used to calculate the preferred value for the above building blocks. The wikipedia pages for them will hopefully contain the formulae.

Note that since electronics relies on the physics of materials, capacitors can behave in a non-ideal way limited by physics and therefore some designs will use certain types or even certain shapes of capacitors, and made of certain materials (cost-performance tradeoff). It can get very advanced; for example, here is a PDF document just dedicated to decoupling. (AVX is a manufacturer of capacitors, so expect them to have lots of useful information).

Some of the other topics require using complex math, depending on how much detail you want to go into. At a high level, it is possible to state things like "a filter will allow certain frequencies to pass". One nice way to think of a capacitor (again, high level) is as a frequency-dependent resistance (actually impedance, but that requires complex math). Again, from that high level, you would not really try to convert that into the building blocks listed above; those building blocks are like well-known templates of designs, so you can directly use the appropriate formulae for calculating the component values.

If you want to be enlightened without any deep math, and want practical guidance, a very good book is 'The Art of Electronics'. If you want the math too, then I can recommend some university-level books, but they are definitely not easy-going and I don't want to scare you ; ) Personally, I'd suggest The Art of Electronics, it is very easy to read.

If you want to experiment, you could try a simulator. Here is a simulation of a filter. You can alter the component values if desired. Notice when you run it, the input signal frequency slowly increases. You can observe the input signal, and the output graphs at the bottom, dynamically.

EDIT: here is a practical example of building block #2 (filter).

Hi Thomas,

They store a certain amount of charge when you stick a voltage across them, but that is much like describing a glass window as "made of silicon dioxide", which while true at a high level, doesn't explain glass nor windows in much detail.

In electronics, there are certain fundamental circuits that can be created using capacitors; these fundamental building-blocks become parts of larger circuits like computers, radios, etc.

Here are some building blocks which can all be created with capacitors and other components:

1. Decoupling

2. Filter

3. DC blocking (related to filter)

4. Tank circuit

5. Timing (often used for resets)

A computer will make extremely extensive use of the first block and #5, whereas a radio will make use of #1,2,4 and an amplifier will make use of #1,2,3.

There are formulas which are used to calculate the preferred value for the above building blocks. The wikipedia pages for them will hopefully contain the formulae.

Note that since electronics relies on the physics of materials, capacitors can behave in a non-ideal way limited by physics and therefore some designs will use certain types or even certain shapes of capacitors, and made of certain materials (cost-performance tradeoff). It can get very advanced; for example, here is a PDF document just dedicated to decoupling. (AVX is a manufacturer of capacitors, so expect them to have lots of useful information).

Some of the other topics require using complex math, depending on how much detail you want to go into. At a high level, it is possible to state things like "a filter will allow certain frequencies to pass". One nice way to think of a capacitor (again, high level) is as a frequency-dependent resistance (actually impedance, but that requires complex math). Again, from that high level, you would not really try to convert that into the building blocks listed above; those building blocks are like well-known templates of designs, so you can directly use the appropriate formulae for calculating the component values.

If you want to be enlightened without any deep math, and want practical guidance, a very good book is 'The Art of Electronics'. If you want the math too, then I can recommend some university-level books, but they are definitely not easy-going and I don't want to scare you ; ) Personally, I'd suggest The Art of Electronics, it is very easy to read.

If you want to experiment, you could try a simulator. Here is a simulation of a filter. You can alter the component values if desired. Notice when you run it, the input signal frequency slowly increases. You can observe the input signal, and the output graphs at the bottom, dynamically.

EDIT: here is a practical example of building block #2 (filter).