audioguru Posted December 10, 2004 Author Report Share Posted December 10, 2004 Hi Andrew,A transistor multivibrator usually works fine with a supply voltage of 6V or less. Above 6V the transistors would need diodes in series with the emitters to protect their b-e junctions from reverse overvoltage breakdown.But the output high-going switching time of a transistor multivibrator may not be quick enough for use as a clock signal for a 74HCxx device that has a maximum recommended input risetime of only 400ns.The reasons that I used a Schmitt trigger inverter as a clock oscillator for this project are: 1) Its output risetime is only about 19ns.2) I can easily control its duty-cycle for PWM brightness adjustment. 3) A Cmos Schmitt trigger oscillator uses hardly any supply current.Hi Guys,I went to my local parts store to buy some more blue ultra-bright LEDs. They didn't have any because someone must have seen my post and bought them all! (How did Dazza get up here?) ;DI ordered them, they will have lots tomorrow. I bought some green ultra-bright LEDs there. Their brightness at only 17mA is awesome like the blue ones. It is too bad that they need about 3V minimum to light. Therefore the project needs a 6v battery (dropping to 4V when drained) instead of a 3V battery for red LEDs.[move]Ultra-bright LEDs are awesome! [/move] Quote Link to comment Share on other sites More sharing options...
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