Wednesday, May 27, 2009

Circuit Theory for Tinkerers

Like it or not, we need some basic Circuit Theory for tinkering in electrical and electronics gadgets.

BTW, changing a plug, replacing a wire, spay some paint does not count as tinkering in my book. When I tinker, I dig deep.

Where did I picked up the circuit theory know-how?

All Engineers took electrical classes somewhere along the academic route; We enter the classroom, went through the motion of listening to the teach/lecturer, collect all the handouts, do some tutorials and off we go to the exams… to return the knowledge in written form. Hopefully, some of these knowledge will residual in our brain. In my case, Ohms Law, power and summation of component value calculation stayed….

Lucky me, enough for tinkering and be dangerous.

Ohms Law

V = I · R

V is for voltage, V is the unitI
I is for current Ampere, A is the unit
R is for Resistance, Ω ohm us the unit.

From here, we can derive the following equations

I = V / R

R= V / I


P = V · I

P for Power or Watt, W is the unit
V for Voltage across the component
I for current running through the component

Summation of Resistance

Series Connected Resistor

Rtotal in series = R1 + R2 + R3 + … + Rn

Rtotal is the resulted total Resistance of the series connected resistors
1, R2….Rn are the Resistance of individual resistor

~handy tips,

When connecting same value resistor in series,

Use This --> Rtotal = Rindividual x Pieces of resistors

Parallel connected Resistor,

Rtotal = ((R1)-1 + (R2)-1 + (R3)-1 + …. + (Rn)-1)-1


Rtotal is the resulted total Resistance of the connected resistors

R1, R2….Rn are the Resistance of individual resistor

~handy tips

When connecting identical value Resistor in parrallell

Rtotal = R1 / pieces of resistor

How to use them?
  • Ohm’s Law enable us to figure out how much voltage is across the component and how much current going through the component.
  • We use this as the minimum required ratings, i.e. current, voltage and watt rating of the components. *PS* For Power rating, give it at least a double,I triple when I have the chance.
  • Summation of resistor allow us to add/reduce Rtotal in the circuit. By changing the Rtotal, when use with Ohm’s Law, we can figure out how to adjust the current and voltage of the circuit and/or components. Which is an essential know-how for tinkering.

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