Electronics: resistors, divider, LED, RC
Everyday bench calculations. You can type values with prefixes: 4.7k, 4k7, 100n, 2u2.
Result
- Tolerance
- ± 5%
- Value range
- 4.465 kΩ … 4.935 kΩ
The tolerance band is usually set apart from the others. Read from the other end.
How to read a resistor colour code
The first two bands (three on precision resistors) are digits, the next is the multiplier and the last is the tolerance. Yellow, violet, red, gold means 47 · 100 = 4.7 kΩ ±5%. On 6-band resistors an extra band gives the temperature coefficient.
LED resistor
The resistor takes up the excess voltage: R = (Vs − Vf) / I. With a 12 V supply, a 2 V red LED and 10 mA you get 1 kΩ. The tool rounds up to the E24 series so the current doesn’t exceed what you asked for.
RC time constant
After τ = R · C a capacitor charges to about 63% of the voltage, and after 5τ it is practically full. The same R and C make a filter with a cut-off frequency of 1 / (2π · R · C).
Common questions
Which end do I read from?
From the end where the bands are closer to the edge. The tolerance band (gold, silver, brown) is usually wider or set apart.
What is the E24 series?
A standard set of 24 values per decade (1.0, 1.1, 1.2 … 9.1) used for 5% resistors. The E96 series has 96 values for 1% resistors.