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--(-Very
Large Files)
--PDF version AN170---- |
 &
See me Move
NE555.pdf
~130-kbytes |
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| The Triggering process
starts when the negative differentiated pulse edge "dips" below 1/3 Vcc,
the
capacitor starts charging.
If the trigger is held below 1/3 Vcc longer than the charge time, the output will remain high even though the capacitor charging cycle is complete; and then only goes low when the trigger rises above 1/3 Vcc. It can be seen, therefore, that it is desirable to have the negative
going trigger pulse to be shorter than the charge time.
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| A Word or Two about using Modulation for AM broadcasting:
Always keep the Pulse Width of the modulation between OR between > 00% & < 50%. At first blush, the reasoning for this may not be obvious: A transmitter is not broadcasting a varying voltage but a varying POWER. That is, the varying modulation voltage is controlling how much Carrier POWER is transmitted. Although the modulating voltage may have a polarity +/-, the RF power leaving the antenna has no polarity. At the receiver the varying power is demodulated/ which is saying it is converted from a varying power to a varying voltage, and if you "AC Couple" the detector's output you again have a varying voltage that has a +/- polarity. --Huh? NOW! At this point you should not have
experienced an "Ah Ha!" --yet.
Notice anything Funny? Right, the second harmonic of the modulation signal increases if the [ > 50%, < 50% ] rule is violated! |
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Triggering
a 555 requires that the "Trigger" input be A.C. coupled. Typical values
can be found in the 555's data sheet & app notes.
However, some values: Rp = 10k, Cc = .001ufd. |
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| The timer receives pulses from the distributor points. Meter M receives a calibrated current thru R 6 when the timer output is high. After time-out, the meter receives no current for that part of the duty cycle. Integration of the variable duty cycle by the meter movement provides a visible indication of engine speed. | |
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Using countdown circuit for LONG delays.
Note relay driving circuit with Protection. |
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445 kHz
Oscillator frequency modulated by a 1-kHz tone. |
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