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| Links to electronic circuits, electronic
schematics, designs for engineers, hobbyists, students & inventors: |
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Frequency
Comparator Draws 8 µA: 03/03/97 EDN-Design Ideas / (Electronic Circuit diagram added 03/03) |
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Frequency Comparator
has Status Output: 12/26/02 EDN-Design Ideas / (Electronic Circuit diagram added 03/03) The original application for the circuit was to
check the number of revolutions of an engine with only one LED as an indicator. The measurement of the number of revolutions usually involves
sensors with a frequency output proportional to the number of revolutions. |
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Frequency
Divider Adapts to I / O Conditions: 09/29/94 EDN-Design Ideas / (Electronic Circuit diagram added 03/03) CanadaThe circuit in Figure 1
accepts an input clock signal, such as from a crystal oscillator, and divides the frequency according to the input divisor word. You can easily
modify the basicdesign of this versatile PLD-based divider to handle different I/O conditions. The design uses the FLEX8000 family of PLDs from
Altera Corp (San Jose, CA). The core of the design generates the appropriate edges to toggle the output T flip-flop to create a clock signal with
a duty cycle of approximately 50%. The input divisor word serves as the reference for the 8COUNT countdown counter. This counter counts down from
the divisor word and raises the COUT flag when the count reaches zero. The complement of COUT synchronously resets the reference value of the
counter to restart the process.... |
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Frequency
Window Comparator has hysteresis: 11/07/96 EDN-Design Ideas / (Electronic circuit added 5/02) The frequency comparator in
Figure 1 uses two VCOs. C1, R1+R2, and the voltage at pin 9 determine the frequency of IC1 (900 Hz). C3, R5+R6, and the voltage at pin 9 determine
the frequency of IC2 (1580 Hz). If fIN is lower than 900 Hz, then the output P2 of phase-comparator 2 in IC1 is high and drives the inhibit input
of IC2 high via the R4-C2 lowpass filter. Consequently, the VCO in IC2 turns off. fIN is therefore higher than IC2's frequency (0 Hz), so the
output P2 of phase-comparator 2 in IC2 goes low, pulling the output low via the R8-C4 lowpass filter. If fIN is higher than 900 Hz and
lower than 1580 Hz, then the output P2 of IC1 goes low and enables the VCO in IC2. IC2's frequency is higher than fIN, so the P2 output of IC2
goes high. Simultaneously, Q1 removes the short circuit across R2, and the frequency of the VCO in IC1 decreases to 870 Hz. The ratio of R2 to
R1+R2 determines the hysteresis of the first comparator.... |
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Make a simple PC
based frequency meter: 04/29/99 EDN-Design Ideas / (added 11/05) A simple, low cost, and precision frequency meter uses only two pins of
a pc parallel port (Figure 1). The TTL-level periodic input signal with frequency fIN connects to the ACK pin of LPT1. This input produces an IRQ7
hardware in- terrupt on every rising edge (Figure 2). The software counts the number of IRQ7 interrupts in the time unit of timebase T. If this
timebase is 1 sec, the frequency of the input signal equals the number of IRQ7 interrupts in 1 sec.... |
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