KrisBlueNZ
Sadly passed away in 2015
Here's an updated schematic with the RF Solutions receiver and some other small additions. There's a lot of extra circuitry to deal with the signals from the manual switch (SWM) and the receiver, but it's really just one IC and a whole lot of resistors and capacitors. Here's a description for the new stuff.
UR generates a +5V regulated rail from the 15V rail coming from the pink noise generator board.
CNR is the connector for the RF Solutions RDF1 receiver board. Pins 18 and 19 configure the board for all momentary outputs. LEDL and SWP are used when "teaching" the receiver to respond to a particular remote control transmitter (see the RF Solutions documentation). Pins 17 and 16 are outputs 1 and 2 respectively; these pulse high then low when the corresponding transmitter button is pressed.
UL is a 74HC14 logic IC, called a "hex inverter with Schmitt trigger inputs". It is a 14-pin device with power and ground on pins 14 and 7, and contains six identical inverter gates, shown individually as triangles named ULA~ULF. Each gate has an input (the wide end) and an output, and it drives its output to the logically opposite state from its input. The Schmitt trigger inputs are mostly significant for ULB, see later.
ULE and ULD form a latch, that "sticks" in one state or the other unless changed by an input pulse. These pulses come through the five diodes that feed into the signals named "+ON" and "+OFF". A positive pulse on the anode of a diode is coupled through the diode and forces the latch into the corresponding state. When the output of the latch (on UL pin 8) is high, this forward-biases QC, which energises relay KC and starts the charging of CT via RR, which causes the noise at the output to ramp up.
Signals that trigger the latch into the ON or OFF state come from the radio receiver, from the manual control switch (via ULB and ULC), and from ULA which forces the latch OFF at power-up via the timing circuit formed by RS and CS. The first four latch trigger signals come from capacitor-resistor circuits that are (loosely) called differentiators.
Any logic signal that is passed through a capacitor then to a resistor to ground will produce a pulse when it changes state. When the incoming signal goes high, it produces a positive pulse at the output of the differentiator; when it goes low, it produces a negative pulse. The pulse duration depends on the time constant of the circuit, which is the product of the resistance and the capacitance (t = RC). (The pulse is not rectangular, it's shaped more like a saw tooth; the time constant is actually the time taken for the pulse to drop to 37% of its initial voltage.)
So a rising edge (transition from low to high) on one of the receiver's outputs is coupled through the capacitor and generates a short positive pulse at the top of the corresponding resistor, and this pulse passes through the diode and triggers the latch into the desired state.
SWM is the manual control switch. The voltage at RM is high when the switch is OFF, and low when it's ON. The 100K resistor and 10 nF capacitor filter out "switch bounce" and ULB buffers and inverts the signal. The gates in UL have Schmitt trigger inputs, which exhibit "hysteresis" and have two trigger voltages. When the input voltage is high and starts to fall, it must drop below the low-going threshold voltage before the gate's output goes high; once this happens, the output remains high until the input voltage exceeds the high-going threshold voltage, which is higher than the low-going threshold. This gives an automatic immunity to poorly defined input voltages between the two threshold voltages, which is important for "cleaning up" the poor-quality signal coming from the mechanical switch. (Mechanical switches produce a lot of noise for a very short time during switching, while the contacts rub and bounce against each other.)
When the switch is turned ON, ULB output goes high, coupling a pulse into the +ON input of the latch; when the switch is turned OFF, ULC output goes high, coupling a pulse into the +OFF input of the latch. The result is that every time the switch changes state, and every time a signal is received by the radio receiver, the latch is triggered into the desired state. Therefore the switch does not actually override the radio receiver; whichever one is operated most recently has priority.
LEDL is the illuminating LED inside SWM. It is driven from the collector of QC, almost in parallel with the relay coil.
I have highlighted the GND rail to make it easier to follow, since the diagram is starting to get messy.
Edit: I've just realised there's a minor simplification I can make to the way the manual switch circuit feeds the latch. I'll upload an updated schematic next time there is a significant change.
UR generates a +5V regulated rail from the 15V rail coming from the pink noise generator board.
CNR is the connector for the RF Solutions RDF1 receiver board. Pins 18 and 19 configure the board for all momentary outputs. LEDL and SWP are used when "teaching" the receiver to respond to a particular remote control transmitter (see the RF Solutions documentation). Pins 17 and 16 are outputs 1 and 2 respectively; these pulse high then low when the corresponding transmitter button is pressed.
UL is a 74HC14 logic IC, called a "hex inverter with Schmitt trigger inputs". It is a 14-pin device with power and ground on pins 14 and 7, and contains six identical inverter gates, shown individually as triangles named ULA~ULF. Each gate has an input (the wide end) and an output, and it drives its output to the logically opposite state from its input. The Schmitt trigger inputs are mostly significant for ULB, see later.
ULE and ULD form a latch, that "sticks" in one state or the other unless changed by an input pulse. These pulses come through the five diodes that feed into the signals named "+ON" and "+OFF". A positive pulse on the anode of a diode is coupled through the diode and forces the latch into the corresponding state. When the output of the latch (on UL pin 8) is high, this forward-biases QC, which energises relay KC and starts the charging of CT via RR, which causes the noise at the output to ramp up.
Signals that trigger the latch into the ON or OFF state come from the radio receiver, from the manual control switch (via ULB and ULC), and from ULA which forces the latch OFF at power-up via the timing circuit formed by RS and CS. The first four latch trigger signals come from capacitor-resistor circuits that are (loosely) called differentiators.
Any logic signal that is passed through a capacitor then to a resistor to ground will produce a pulse when it changes state. When the incoming signal goes high, it produces a positive pulse at the output of the differentiator; when it goes low, it produces a negative pulse. The pulse duration depends on the time constant of the circuit, which is the product of the resistance and the capacitance (t = RC). (The pulse is not rectangular, it's shaped more like a saw tooth; the time constant is actually the time taken for the pulse to drop to 37% of its initial voltage.)
So a rising edge (transition from low to high) on one of the receiver's outputs is coupled through the capacitor and generates a short positive pulse at the top of the corresponding resistor, and this pulse passes through the diode and triggers the latch into the desired state.
SWM is the manual control switch. The voltage at RM is high when the switch is OFF, and low when it's ON. The 100K resistor and 10 nF capacitor filter out "switch bounce" and ULB buffers and inverts the signal. The gates in UL have Schmitt trigger inputs, which exhibit "hysteresis" and have two trigger voltages. When the input voltage is high and starts to fall, it must drop below the low-going threshold voltage before the gate's output goes high; once this happens, the output remains high until the input voltage exceeds the high-going threshold voltage, which is higher than the low-going threshold. This gives an automatic immunity to poorly defined input voltages between the two threshold voltages, which is important for "cleaning up" the poor-quality signal coming from the mechanical switch. (Mechanical switches produce a lot of noise for a very short time during switching, while the contacts rub and bounce against each other.)
When the switch is turned ON, ULB output goes high, coupling a pulse into the +ON input of the latch; when the switch is turned OFF, ULC output goes high, coupling a pulse into the +OFF input of the latch. The result is that every time the switch changes state, and every time a signal is received by the radio receiver, the latch is triggered into the desired state. Therefore the switch does not actually override the radio receiver; whichever one is operated most recently has priority.
LEDL is the illuminating LED inside SWM. It is driven from the collector of QC, almost in parallel with the relay coil.
I have highlighted the GND rail to make it easier to follow, since the diagram is starting to get messy.
Edit: I've just realised there's a minor simplification I can make to the way the manual switch circuit feeds the latch. I'll upload an updated schematic next time there is a significant change.
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