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Further Explanation of Block Diagram
Tuesday, 14 August 2012 ?
- The two Binary Mixers, IC3a and IC3b ( see the block diagram ), are each based on one half of a CMOS 4520 dual binary counter. These mix a signal from high frequency oscillator IC1a ( as it incorporates the sensor, we call it the "sensor H.F.O " ) with a benchmark frequency produced by IC2a ( Benchmark H.F.O ). Both oscillator are based on the 7556 dual timer i.c, and both are tuned roughly to the same frequency of around 100kHz.
- Sensor H.F.O. IC1a is an RC oscillator, so when metal sensor is approached, C increases and frequency drops, creating a frequency difference ( difference frequency ) between the two h.f.o. oscillator. The point at which this difference frequency drops to zero is called "the null point".
- The difference frequency is further mixed with the output of low frequency oscillator ( L.F.O ) IC1b - also based on the 7556 i.c.- so that the smallest difference frequencies only are detected. These are indicated audibly by a piezoelectric sounder ( WD1 ), in the form of crackles or a beep.
- The difference frequency is fed back to the Benchmark h.f.o. IC2a through resistor R6 to improve the circuit stability, and the unit has intelligent frequency compensation. An important feature of the circuit is that the frequency of IC2a, the benchmark h.f.o. is fuzzed with the assistance of IC1b, the low frequency oscillator (l.f.o). the effect of such fuzzing is illustrated in figure below :
"Fuzzing" the benchmark frequency.
- The low frequency oscillator IC1b creates a "detection zone" around the benchmark frequency, so that the fluctuating frequency of IC1a is detected as soon as it strays into the detection zone. this overcome the possibility of the two h.f.o.'s " locking on " to each other near the null point, and also assists with adjustment of the circuit. it is easy to tune in to a detection zone than a spot frequency.
- Finally, a short delay is provided at switch on, through capacitor C11 and resistor R9, so that the user has time to step out of range before monostable IC2b and the relay are activated.
" It is no use saying, 'We are doing our best.' You have got to succeed in doing what is necessary. "
Thanks for reading :)
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 Further Explanation of Block Diagram
- The two Binary Mixers, IC3a and IC3b ( see the block diagram ), are each based on one half of a CMOS 4520 dual binary counter. These mix a signal from high frequency oscillator IC1a ( as it incorporates the sensor, we call it the "sensor H.F.O " ) with a benchmark frequency produced by IC2a ( Benchmark H.F.O ). Both oscillator are based on the 7556 dual timer i.c, and both are tuned roughly to the same frequency of around 100kHz.
- Sensor H.F.O. IC1a is an RC oscillator, so when metal sensor is approached, C increases and frequency drops, creating a frequency difference ( difference frequency ) between the two h.f.o. oscillator. The point at which this difference frequency drops to zero is called "the null point".
- The difference frequency is further mixed with the output of low frequency oscillator ( L.F.O ) IC1b - also based on the 7556 i.c.- so that the smallest difference frequencies only are detected. These are indicated audibly by a piezoelectric sounder ( WD1 ), in the form of crackles or a beep.
- The difference frequency is fed back to the Benchmark h.f.o. IC2a through resistor R6 to improve the circuit stability, and the unit has intelligent frequency compensation. An important feature of the circuit is that the frequency of IC2a, the benchmark h.f.o. is fuzzed with the assistance of IC1b, the low frequency oscillator (l.f.o). the effect of such fuzzing is illustrated in figure below :
"Fuzzing" the benchmark frequency.
- The low frequency oscillator IC1b creates a "detection zone" around the benchmark frequency, so that the fluctuating frequency of IC1a is detected as soon as it strays into the detection zone. this overcome the possibility of the two h.f.o.'s " locking on " to each other near the null point, and also assists with adjustment of the circuit. it is easy to tune in to a detection zone than a spot frequency.
- Finally, a short delay is provided at switch on, through capacitor C11 and resistor R9, so that the user has time to step out of range before monostable IC2b and the relay are activated.
" It is no use saying, 'We are doing our best.' You have got to succeed in doing what is necessary. "
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