Uploaded September 2012 | Updated September 2026, 1 week ago
I have placed a couple of 555 circuit examples below for your convenience. Play with different component values and use the formulas mentioned earlier to calculate your results. Things to remember: For proper monostable operation with the 555 timer, the negative-going trigger pulse width should be kept short compared tot he desired output pulse width. Values for the external timeing resistor and capacitor can either be determined from the previous formulas. However, you should stay within the ranges of resistances shown earlier to avoid the use of large value electrolytic capacitors, since they tend to be leaky. Otherwise, tantalum or mylar types should be used. (For noise immunity on most timer circuits I recommend a 0.01uF (10nF) ceramic capacitor between pin 5 and ground.) In all circuit diagrams below I used the LM555CN timer IC from National, but the NE555 and others should not give you any problems
Dark Detector: It will sound an alarm if it gets too dark all over sudden. For example, this circuit could be used to notify when a lamp (or bulb) burns out. The detector used is a regular cadmium-sulphide Light Dependent Resistor or LDR, for short, to sense the absense of light and to operate a small speaker. The LDR enables the alarm when light falls below a certain level.
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Please watch: "Lifi Communication by Arduino UNO Download Project"
youtube.com/watch?v=c4gC8dbaiZg
-~-~~-~~~-~~-~-
I have placed a couple of 555 circuit examples below for your convenience. Play with different component values and use the formulas mentioned earlier to calculate your results. Things to remember: For proper monostable operation with the 555 timer, the negative-going trigger pulse width should be kept short compared tot he desired output pulse width. Values for the external timeing resistor and capacitor can either be determined from the previous formulas. However, you should stay within the ranges of resistances shown earlier to avoid the use of large value electrolytic capacitors, since they tend to be leaky. Otherwise, tantalum or mylar types should be used. (For noise immunity on most timer circuits I recommend a 0.01uF (10nF) ceramic capacitor between pin 5 and ground.) In all circuit diagrams below I used the LM555CN timer IC from National, but the NE555 and others should not give you any problems
Dark Detector: It will sound an alarm if it gets too dark all over sudden. For example, this circuit could be used to notify when a lamp (or bulb) burns out. The detector used is a regular cadmium-sulphide Light Dependent Resistor or LDR, for short, to sense the absense of light and to operate a small speaker. The LDR enables the alarm when light falls below a certain level.
-~-~~-~~~-~~-~-
Please watch: "Lifi Communication by Arduino UNO Download Project"
youtube.com/watch?v=c4gC8dbaiZg
-~-~~-~~~-~~-~-
