>The first stage is actually a 303MHz oscillator that is operating all the time.
It produces a clean 303MHz signal and this frequency is too high to be detected or processed by the 4069 chip, as the chip will only operate to about 1MHz.
The theory behind using this type of stage is quite simple.
It is easier to "upset" or modify a stage that is already oscillating, rather than get a non-oscillating stage to begin oscillating.
There are all sorts of electromagnetic radiation at 300MHz and the 2-turn coil picks up all this noise.
The 303MHz oscillator is firstly set into operation by the noise produced by the transistor and this is passed to the tank circuit made up of the 2-turn coil and 2p capacitor as a parallel tuned circuit. The transistor keeps amplifying this until it gets to a stabilized point where the collector is producing "hash" (junk) of about 300mV.
When the transmitter is activated, the receiver circuit will detect a signal as small as a few micro-volts and the 32 kHz signal will be included with all the other noise.
There is a little bit more behind this receiving stage, than first meets the eye.
The stage is actually a transmitter, but we will still call it the receiver circuit. Yes, it is a very weak transmitter and it fills the surrounding with a clean 303MHz signal. When the 303MHz signal from the transmitter enters this space, the signals interfere with one another and the receiver takes more and less current as it tries to maintain the signal strength. When the 32 kHz signal is present, the receiver takes a varying current that corresponds to the 32 kHz signal and this is how the receiver circuit produces the waveform to correspond to the 32 KHz.
A low-impedance path to the 0v rail is provided for the emitter by using a 82uH choke and a 2n2 capacitor across a 560R resistor. This low impedance path is needed so that the transistor has a high gain.
The circuit is put into very delicate oscillation by using a 1k5 from the positive rail.
It operates from 3v and the current taken by this stage is less than 1mA.
The first inverter has a 1M connected between the output and input to set it to mid rail so it becomes a high-gain amplifier.
The second and third inverters also amplify the signal and on pin 6 we have a signal greater than 0.6v containing a lot of noise and an identifiable 32 kHz waveform.
The 32 kHz crystal only allows the 32 kHz signal to pass and the base of the transistor sees a very clean signal. Any other frequencies will not appear on the base of the transistor. The 32 kHz is further amplified with two more stages and appears at pin 10 of the chip.
It is then passed to a diode pump that charges a 47u electrolytic.
Normally, this electrolytic is uncharged and pin 8 is HIGH. The PNP transistor is not turned on and the sound chip is silent.
But when the electrolytic charges, the transistor turns on and the sound chip operates.
It produces a clean 303MHz signal and this frequency is too high to be detected or processed by the 4069 chip, as the chip will only operate to about 1MHz.
The theory behind using this type of stage is quite simple.
It is easier to "upset" or modify a stage that is already oscillating, rather than get a non-oscillating stage to begin oscillating.
There are all sorts of electromagnetic radiation at 300MHz and the 2-turn coil picks up all this noise.
The 303MHz oscillator is firstly set into operation by the noise produced by the transistor and this is passed to the tank circuit made up of the 2-turn coil and 2p capacitor as a parallel tuned circuit. The transistor keeps amplifying this until it gets to a stabilized point where the collector is producing "hash" (junk) of about 300mV.
When the transmitter is activated, the receiver circuit will detect a signal as small as a few micro-volts and the 32 kHz signal will be included with all the other noise.
There is a little bit more behind this receiving stage, than first meets the eye.
The stage is actually a transmitter, but we will still call it the receiver circuit. Yes, it is a very weak transmitter and it fills the surrounding with a clean 303MHz signal. When the 303MHz signal from the transmitter enters this space, the signals interfere with one another and the receiver takes more and less current as it tries to maintain the signal strength. When the 32 kHz signal is present, the receiver takes a varying current that corresponds to the 32 kHz signal and this is how the receiver circuit produces the waveform to correspond to the 32 KHz.
A low-impedance path to the 0v rail is provided for the emitter by using a 82uH choke and a 2n2 capacitor across a 560R resistor. This low impedance path is needed so that the transistor has a high gain.
The circuit is put into very delicate oscillation by using a 1k5 from the positive rail.
It operates from 3v and the current taken by this stage is less than 1mA.
The first inverter has a 1M connected between the output and input to set it to mid rail so it becomes a high-gain amplifier.
The second and third inverters also amplify the signal and on pin 6 we have a signal greater than 0.6v containing a lot of noise and an identifiable 32 kHz waveform.
The 32 kHz crystal only allows the 32 kHz signal to pass and the base of the transistor sees a very clean signal. Any other frequencies will not appear on the base of the transistor. The 32 kHz is further amplified with two more stages and appears at pin 10 of the chip.
It is then passed to a diode pump that charges a 47u electrolytic.
Normally, this electrolytic is uncharged and pin 8 is HIGH. The PNP transistor is not turned on and the sound chip is silent.
But when the electrolytic charges, the transistor turns on and the sound chip operates.
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