Diy Christmas lights: Difference between revisions
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== Theory == | == Theory == | ||
Use leds in series, as parallel leds might light on uneven brightness. | |||
Usually the longer led is the + lead. | |||
=== LEDs and wiring === | === LEDs and wiring === | ||
* Red and yellow led: 2 V | |||
* Green and blue led: 2.9 V | |||
* White: 3.3 V | |||
Seven blue leds makes <math>7\times 2.9 V =20.3 V</math>, and white blue leds drops the voltage by <math>7\times 3.3V=23.1 V</math>. | |||
If we use simple AA batteries, we will need <math>14\times 1.5= 21 V</math> or <math>16\times1.5 = 24 V</math>. Quite many. . . | |||
However, if we wire them alternately, it makes <math>3\times2.9V=8.7V</math> and <math>4\times2.9V=11.6V</math> for blue leds and <math>3\times3.3V=9,9V</math> and <math>4\times3.3V=13,2V</math> the white leds. Thus, we need only six (6) or eight (8) batteries; or 7 and 9 in the case of white leds. | |||
=== Photodiode and transistors === | === Photodiode and transistors === | ||
We can use a photodiode and transistor to turn a led on. The example given by EviMadScientist uses | |||
* a battery, | |||
* an LTR-4206E phototransistor (in a black package: blocks visible light; sensitive to IR) | |||
* a 2N3904 transistor, | |||
* and a 1 k resistor. | |||
[[File:Photodiode.svg|thumb|A simple photodiode circuit by EvilMadScientist]] | |||
References | |||
* https://www.evilmadscientist.com/2007/a-simple-and-cheap-dark-detecting-led-circuit/ | |||
* CdS (“LDR”) phototransistor circuits | |||
== result == | == result == | ||
Latest revision as of 21:05, 13 November 2022
Introduction
Make a simple battery powered Christmas light with seven (7) leds.
Theory
Use leds in series, as parallel leds might light on uneven brightness.
Usually the longer led is the + lead.
LEDs and wiring
- Red and yellow led: 2 V
- Green and blue led: 2.9 V
- White: 3.3 V
Seven blue leds makes , and white blue leds drops the voltage by . If we use simple AA batteries, we will need or . Quite many. . .
However, if we wire them alternately, it makes and for blue leds and and the white leds. Thus, we need only six (6) or eight (8) batteries; or 7 and 9 in the case of white leds.
Photodiode and transistors
We can use a photodiode and transistor to turn a led on. The example given by EviMadScientist uses
- a battery,
- an LTR-4206E phototransistor (in a black package: blocks visible light; sensitive to IR)
- a 2N3904 transistor,
- and a 1 k resistor.
References
- https://www.evilmadscientist.com/2007/a-simple-and-cheap-dark-detecting-led-circuit/
- CdS (“LDR”) phototransistor circuits
