Some general electronic questions

I am a beginner and I have a few questions that a beginner might have. So here goes my questions:

  1. What are operational-amplifiers? How do they work and can you give me examples of a few common ones?

  2. What is GSM and what is GPRS in simple words (Wikipedia is complex) ? What is the difference between them and GPS?

  3. When I was reading about 74HC595 Shift Register I found a term very commonly used: "Daisy Chain" What is that?

  4. What is ADC and DAC on a Microcontroller? Also What are bits in those pins (for e.g. 8 bit ADC, 10 bit ADC etc)

  5. What is RTC IC and how to use it with my Arduino?

I have a question not from this category but please answer this: Should I consider buying the 5V 16MHz or the 3.3V 8MHz Arduino Pro mini. What are the differences between those two? Also, would a CH340G Breakout board work with the Pro Mini or should I buy the FTDI only?

I also have other questions, but I forgot them :slightly_frowning_face:. When I remember, I'll ask them in this post.


Is Google broken again?

I hate it when that happens.

Feels like homework to me…

Starter for ten - daisy chain -number of daisies linked together , term can be applied to other things I suspect …discuss.image

Ok,ok. I'll search in Google. No more fun of me here.

At least answer the Pro MIni question...

Depends on what you want to do , so impossible to answer your final question about which device to buy . While you’ve got Google fired up , you can look at spec of each device and decide what you want . ( cf “ horses for courses”)

IMO … If you are starting out buy a genuine UNO from this site .

One is 5V 16MHz and the other 3.3V 8MHz … :cold_face: :innocent:

The one you buy depends on the needs…

I'll take a shot a couple of these...

An op-amp is a "universal" low power amplifier chip. An ideal op-amp has infinite "open loop" gain and real op-amps have very high gain. That allows you to build amplifier where the gain is controlled by the ratio of two resistors. They can be used as a microphone preamp or to amplify other low-level signals.

They can also be used to make a high-pass or low-pass (or bandpass or band-reject) filter. Open loop (nearly infinite gain) they can be used as an analog comparator where the output is at the minimum voltage when the input is below the reference and "slammed" to the maximum output voltage when the input is above the reference. Here is a "famous" collection of op-amp circuits. (These are not complete schematics. Op-amps require power, and usually plus and minus power supplies with bypass capacitors on the power pins, etc.)

It simply means connected one-after-another. They are serially addressed and they have 8 outputs which can be connected to LEDs (etc.), If you daisy-chain 3 of them you can address/control 24 LEDs independently. You can daisy-chain an almost unlimited number of chips and individually control a huge number of LEDs with just a few Arduino output pins.

Analog-to-digital and digital-to-analog converter. An ADC has an analog input and a DAC has an analog output. The bits are binary (base-2) "digits".

The basic Arduino has a 10-bit ADC with a default 5V reference. With 5V on the ADC input you get the binary value of 1111111111 which is as high as you can count with 10 bits. We don't normally see the binary value and that converts to a decimal value of 1023. With 2.5V you get a decimal value of half the maximum (511 or 512).

The regular Arduino doesn't have a DAC (no true analog output). analogWrite() puts out PWM which can "simulate" analog to control the speed of a motor or change the apparent brightness of an LED, etc.

Real Time Clock = Time of day clock. An RTC module often also gives you the date. The Arduino only has a built-in clock that gives you the number of milliseconds since the Arduino was booted (IIRC it "rolls over" after about 45 days) but it doesn't know the time-of-day.

Thanks a lot @DVDdoug , you explained me all this in a much simple way. :slight_smile:

By this do you mean a voltage divider of two resistors?


I have got a question that might seem a bit strange:

If I make any circuit using PNP Transistor can I also make it using it's complementary NPN transistor?

For E.g.

(Got this circuit on net for a DIY Automatic Sanitizer dispenser)
What changes do I need to make in this circuit if I want to use TIP31C which is a NPN transistor?

EDIT: Another doubt, When any object comes in front of the sensor, I read that sensor OUT goes LOW. In the above circuit, This would lead to current flowing out of PNP transistor BASE to the OUT of the Sensor (this is how PNP transistor turn ON-allowing current to flow from E to C). Wouldn't this damage the sensor?

IF the output of the prox sensor IS open collector then the current frrom the transisistor is limited by the 1K resistor and no damage is incurred by the sinking ! suggest a flyback diode across the load if using an inductive load (like a pump) in your diagram.

What is an op amp and how can you use it?

What is an ADC?

Hello, @johnerrington I just read your guide of Op-amps yesterday, A BIG THANK YOU to you for this wonderful guide. At Least I understood some of the common applications and terms regarding Op-amps I got to understand.

Hello @cherk Thanks for your explanation. I actually don't know if the pump is Inductive or not (I purchased it from a local store who only told 3-6V input voltage as the spec). I will look into what a flyback diode is and test it and return to you with the answers.

Pumps use motors, motors are inductive, its an inductive load!

Absolutely, all polarities just flip.

Hello Friends, I am back with a new set of doubts... :thinking:

  1. I recently created a circuit on Falstad using ideal op-amps. Now I want to convert the same circuit into real op-amp. Can you suggest an op-amp for the same and tell me what changes do I need to do to my circuit?
    Circuit Link:
    Circuit Image:

  2. What will happen if I input 9V AC to my LM7805? Will it output DC?

  3. Which driver (other than the FTDI) do you recommend to use with the Pro Mini?

  4. Can you give the names of some common schottky diodes you use?


The first opamp is being used as a comparator - note that not all opamps can be used as comparators, and in general its far better to use a comparator if you use positive feedback anyway.

However most comparators don't have push-pull outputs but rather open-collector outputs for use with logic circuitry or arbitrary supply voltage.

So perhaps find a dual opamp which allows input differential voltage of the full supply swing (most datasheets for opamps will show the input differential swing limit).

You probably should go for fully rail-to-rail opamp designed for use with 5V if you want to interface with an Arduino.

You probably also would want to define a 2.5V pseudo-ground for the opamps so its mid-rail between 5V and 0V.

You'll struggle to find a 10µF film capacitors for the second part - perhaps change the R and C values by a factor of ten (R 10 times larger, C ten times smaller).

It will burn up instantly. Linear regulators are DC only.

No, I usually do a parametric search for parts so I find the latest and cheapest for my immediate requirements. And I mainly use surface-mount which may not be what you require - you know about electronics suppliers websites having great search facilities for parts?

It is better to use 9V DC or 5V DC without regulator. If you must use 9V AC for some reason you need to rectify it first. And use a "large" storage capacitor between the bridge and the regulator.