Cards Theory

Notes in short

How long will your battery charge last?

Time [ hours ] = Battery capacity [Ah] / Current [A]. For example, a 10 Ah battery will power a 0.1 A load for 100 hours.

How big a battery do I need to power a load for a given time?

Battery capacity [Ah] = Load current [A] * Time [hrs]


Battery capacity [Wh] = Watt * hrs  ( This is a true way of  measuring battery capacity because it takes voltage into account )

What are Decoupling capacitors?

A decoupling / bypass capacitor is a capacitor used to decouple one part of the electrical network from another. Noise caused by other circuit elements is shunted through the capacitor, reducing the effect it has on the rest of the circuit. It’s hard to demonstrate whether decoupling capacitors are really necessary, but it never hurts to include them. As a general rule, every IC should have decoupling capacitors at every power pin. 0.1uF is a standard value, but you need to check the datasheet. The job is to supress high-frequency noise in power supply signals. They take tiny voltage ripples, which could be otherwise harmful to delicate ICs, out of the voltage supply.  Decoupling capacitors connect between 5V, 3.3V and ground. If somebody says they didn’t use decoupling capacitors and it works fine, that’s like saying they only put 2 lug nuts on each wheel, and it works fine. Notice LM7805 with two decoupling capacitors.

What is more dangerous – current or voltage?

A combination of both ? 😀

Why do we see multiple bypass capacitors?

EEVblog – Bypass Capacitor Tutorial

Recommended  good quality pyroelectric detector

LHi968 : Here. It is one of the best in the market and graded for lower white light sensitivity.

What are Electrolytic Capacitors?

These capacitors include both aluminium and tantalum electrolytics. Tantalum electrolytic capacitors have larger capacitance per volume ratios when compared to the aluminium ones. A majority of these capacitors are polarized. Electrolytic capacitors, when compared with nonelectrolytic ones, typically have greater capacitances but have poor tolerances ( extent to which the actual capacitance is allowed to vary from its nominal value ), bad temperature stability, high leakage and short lives.

What are Ceramic Capacitors?

A very popular nonpolarized capacitor that is small and has poor temperature stability + poor accuracy. It contains a ceramic dielectric and is often used to bypass and coupling applications.

What are Mylar Capacitors?

Popular nonpolarized capacitor that has low leakage current but poor temperature stability.

What are Mica Capacitors?

This is an extremely accurate device with very low leakage currents. These capacitors have small capacitances and are often used in high-frequency circuits like the RF ones. They are very stable under variable voltage and temperature conditions.

Repair guide for everything?

Real vs Ideal Battery Discharge Curve

Taken from EEVblog

What is the effect of cut off voltage on battery capacity?

Most 3.7 Li-ion are with an end charge of 4.2V ( 3.7V is the nominal voltage )

A well designed product will have as low cut off voltage as possible and will operate all the way down.

What is JTAG?

Taken from EEVblog ( Here )

JTAG stands for Joint Test Action Group. You may have heard the term or used in terms of programming a microcontroller or an FPGA or as a debugging interface but, in fact, it wasn’t even originally designed for the above mentioned tasks. Manufacturers had real lot of trouble in testing the assembled PCBs ( packages got very dense ). They wanted to come with a standard to embed some hardware into the chips so that we can use them to test them. More details in the video.

Getting Started with Arduino UNO

Instructable link : Here

Guide for Using a GPS Sensor

Instructable link : Here

What are Flex Circuits?

They can be shaped, bent or twisted. Both rigid and flex circuits serve, the same function, which is connecting electrical components. Flex circuits may eliminate the cost of connectors or wire harnesses.

What is IC 7805?

7805 ( xx in 78xx indicates the output voltage it provides ) provides+5V regulated power supply with provisions to add a heat sink. If the regulator does not have a heat sink to dissipate the heat ( difference between voltage input and 5V is released as heat ). Look at the datasheet for more information : Here

What is Flash Memory?

Flash memorywas first developed in 1980s and is a form of non-volatile memory which uses the same method of programming as the standard EPROM. It is slower than other forms of memory and has limited number of read/write cycles. Have a look at storage conditions : Here

What are Vacuum Tubes?

Even today, vacuum tubes are used still used in guitar amplifiers and much more and people like the sound produced by these devices. It is based around the basic concept of thermionic emission. A heated element in a vacuum emitted electrons that would normally remain in the vicinity of this heated element because of the charge attraction. If a second electrode was placed into the vacuum and a high positive potential placed on it, then the electrons would be attracted away from the heated element towards this element with a high potential. As a result a current would flow in this direction. A third element or the grid is placed between the structure between the two electrodes that has a variable potential and is used to control the flow of electrons. [ TO BE EDITED + CONTENT NEEDS TO BE ADDED ]

What are the basic elements in a power supply?

  1.  Input Transformer : Is used to transform the incoming line voltage down to the required level of the power supply.
  2.  Rectifier : Convert the signal form an AC format into raw DC
  3.  Smoothing : Filter capacitors help to smoothen out the ripple
  4.  Regulator : Provides a constant output

What are various forms of power supplies?

  1.  Unregulated : It simply consists of rectifier section followed by a capacitor and inductor smoothing without any regulation to steady the voltage. It was used many years ago.
  2.  Regulated : They incorporate a voltage reference and the output voltage is comapred to this and altered accordingly by control circuitry. Linear regulated power supplies are used where low noise and ripples are required and use a linear regulator element to drop voltage. Switching power suppliees uses a large output reservoir capacitor with less amount of heat to be removed. EMC issues may cause interference. Unllike a linear power supply, the pass transistor of an SMPS continually switches b/w low-dissipation, full-on and full-off states and spends very little time in the high dissipations transitions. Ideally, SMPS dissipates no power. For more details : Wikipedia-SMPS

What are Fuses and Circuit Breakers?

They are devices designed to protect circuits from excessive current flow, which are often a result of large currents that result from shorts or sudden power surges. A fuse contains a narrow strip of metal that is designed to melt when current flow exceeds its current rating, thereby interrupting power to the circuit. Once a fuse blows, it must be replaced with a new one. A circuit breaker is a device which can be reset after it “blows”. When the curretn flow exceeds a breaker’s current rating, a bimetallic strip heats up and bends which “trips” the latch.

What are the various types of fuses and circuit breakers?

Glass and Ceramic

These are made by encapsulating a current-sensitive wire or ceramic element within a glass cylinder. Fuses may be fast-acting or time-lagging. Current ratings range from around 1/4 to 20A, with voltage ratings of 32, 125, 250V.


These are fast-acting fuses with bladelike contacts. Current ratings range from 3 to 30A, with voltage ratings of 32 and 36V and are colored coded according to the rating.

Circuit Breakers

Some have manual resets, while other have thermally actuated resets. Main-line circuit breakers are rated at 15 to 20A and smaller ones may be rated as low as 1A.

How to enclose circuits?

Circuits are typically enclosed in either an aluminium or plastic box. Aluminium enclosures are often used when designing high-voltage devices, wherea the plastic ones for lower-voltage applications. Also, ground it.

What is Heat?

Correct definition: When two or more systems are in thermal contact , internal energy flows from the system at higher temperature to the system at lower temperature. The “internal energy in transit” between two bodies is called heat.

What is temperature?

Correct definition: Physical property which determines the direction of flow of heat when two bodies are brought in contact.

What is a Slow-blow Fuse?

It is a type of fuse which can handle a temporary surge current which exceeds the current rating of the fuse. It does not blow for a temporary surge current; it must receive a sustained elevated current above its current rating.

Why Gold Plated Probes Matter?

You can find the video from : Here

What is Coupling Capacitor?

A capacitor which is used to couple or link only the AC signal from one circuit element to another. The capacitor block DC component and the value of the coupling capacitor depends on the frequency of thw AC signal being passed through.

What are Zener Diodes?

A Zener Diode is a device that acts as a typical pn-junction diode when it comes to forward biasing, but it also has the ability to conduct in the reverse-biased direction when a specific breakdown voltages in the range of a few volts to a hundred volts. They are frequently used in voltage-regulator applications.

What are EMI filters?

EMI can be in the form of conducted EMI, which means the noise travels along electrical conductors, wires or components such as inductors, capacitors. Electrical noise can be in the form of radiated EMI, noise that travels through the air which is controlled by providing metal shielding. Most electrical and electronic devices can generate and/or be affected by EMI. Sources include motors, microwave ovens and SMPSs. High speed switching in SMPS generates unwanted EMI witihn the SMPS. It is the function of an EMI fiter to keep any internal generated noise  witihn the device and prevent any AC line noise from entering the device.

What are Optocouplers/Optoisolators?

They are devices that interconnect two circuits by means of an optical interface. For example, a typical optoisolator may consist of an LED and a phototransistor enclosed in a light-tight container. The LED portion of the optoisolater is connected to the soure circuit, whereas the phototransistor portion is connected to the detector circuit. One circuit can be used to control another circuit without undesirable changes in voltage and current that might occur if the two circuits were connected electrically. Interrupter is a device that contains an open slot between the source and sensor through which a blocker can be placed to interrupt light signals.

How to make an ‘intelligent’ bicycle lock?

Details available: Here

Darlington Pair

By attaching two transistors as shown above, a larger current-handling, larger Hfe equivalent transistor circuit is formed. The combination is referred to as Darlington Pair. The equivalent Hfe for the pair is equal to the product of the individual transistor’s Hfe values. They are used for large current applications and have slower response times ( it takes longer for the top transistor to turn the lower transistor on and off. They hve twice the base-to-emitter voltage drop of 1.2V instead of 0.6V. The circuit above uses BD679 (Datasheet : Here). Make sure you see the datasheet of your own manufacturer.


UM3561 is a CMOS LSI IC commonly used in alarm and toy applications. It is able to generate police siren, ambulance siren, fire engine siren and machine gun sound just by changing some connections. It’s a low power IC which can work down to 2.4V. Datasheet : Here.

SEL1 SEL2 Sound Effect
NC NC Police Siren
VDD NC Fire Engine Siren
VSS NC Ambulance Siren
X VDD Machine Gun