Here 4052 is used as an analog multiplexer, U3A TL062 opamp is wired as a 1mA Constant Current Source. It pumps 1mA into U2 4052 pin 13 X . Depending on BCD code on inputs A, B of 4052 the current is routed to any one of the four RTD 100E, whose one end is connected to X0-X3. The current then flows to GND thru the Platinum 100E resistance. The Y0-Y3 monitors the mV developed on RTD in tandem with X0-X3 positions. Like a ganged rotary switch. The Output mV at Y is the mV of Active Channel as selected by the BCD of 4029.
RTD Pt-100 Four Point Alarm – del90001
The BCD is provided by 4029 counter which is clocked by a 555. U5A cancels out the 100E mV (1mA * 100E) of a cold RTD and Amplifies the differential mV. This output of U5A is in proportion with measured temperature. U5B compares the mV that was obtained with a preset mV of POT1, which is a user setting called setpoint. The difference is amplified by U5B which is saturated by U3B comparator which adds a little hysteresis too. R7-C2 further dampen and slow the response. This finally drives Q2 to provide a Logic Signal indicating if temperature is below or above setpoint.
Four points in a Closed Loop Temperature Control System is Monitored and a Alarm set to go off when the temperature goes beyond the set limit.
A, B, and C are the Digital Control for x, y and z input and output pairs.The voltage at Vinx is stored in C1 when A goes high, when A is low the voltage stored in C1 is read by buffer U2A.
It could be used in DMM circuits as Analog Memory DMM range, AC-DC mode, logic control
Another application of Mux 8 Channel 4-20mA Analog Multiplexer
The stby or standby input should be low when sample and hold is operating. If stby is taken high then C1 Cap is isolated and leakage is minimum. The supply of +/- 7.5V is chosen as OFF resistance of 4053 is high at this supply.
A sample and hold is like an analog memory. If The digital control A is low 4066 switch is open, and when A is high switch is closed. U2B is a buffer so as to ensure quick charging of C1 thru 4066 on resistance of 100E.
Mixed and Interface Circuits
U2A is a FET input opamp buffer which does not load or drain the cap C1. When A goes high the input analog sample is stored in C1. A has to be high for say 10*1uF*100E = 1mS, so that a proper stable sample is stored. When A is low C1 undergoes very slow discharge as opamp input resistance and 4066 off resistance is in giga ohms. The accuracy of reading Vout falls with respect to time due to leakage currents.
CD4046 is a PLL or phase lock loop, it mainly consists of a VCO and phase comparators. This is a component in FM demodulation and modulation.
Mixed and Interface Circuits
It is used in a closed loop control to maintain a stable frequency. The Circuit above is good for learning the full use of a small Dual Trace Scope. The Circuit has both Analog and Digital areas and is a part of communication.
Read the pages above for building more Knowledge on PLL
LM311 is a comparator, It operates from single 5V supply or dual supplies,input current 150 nA, 50 V-50 mA output drive capability. TTL-CMOS compatible output.
Even LM324 used as a comparator Water Level Indicator with Reed Relays
The Output is open collector so it can sink current but cannot source, a totem pole output can source and sink. In this Circuit R2 is the source or pull-up.
The Output being high or low depends on which input is more dominant or positive. If + or non-inverting input is more positive than the – inverting input then output of LM311 is high impedance or high Z as output transistor of LM311 is turned off, but output goes high due to R2 pull-up 1K, so you can apply a load of 10K and above for source. When the – input or inverting input is more positive, output goes Low as transistor turns on, now a current of upto 50mA can sink here, a LED or Relay can be driven.
Mixed Circuits Analog with Digital
On turn on C2 capacitor is discharged and pin 3 the inverting input is at a lower potential than pin 2 the non-inverting which is at 2.5V. Hence output goes high and C2 starts charging thru R5, When C2 charges a little beyond 2.5V pin 3 is more dominant and output goes low now, this slowly discharges the C2 bringing the voltage at pin 3 again below 2.5V so output goes high again. This process goes on, hence it oscillates. The charging and discharging is at the rate of R5 * C2 approx. , R3 serves as hysteresis or feedback to ensure clean turn on and off.
CD4538 is a dual Monostable Multivibrator. When you trigger the chip the output sends off one single pulse or one high-low event.
Mixed Circuits Analog with Digital
The T+ pin 4 of U1a is the positive edge trigger or raising edge trigger input, the T- pin 5 is falling edge or negative edge trigger input. Now see the image of the single pulse above which shows both the edges, If this is the input pulse at pin 5 then the falling edge turns the output pin 6 from low to high, this output remains high for time T = R2 * C1 and then goes low again, The output Q at pin 6 also looks like the image of pulse above.
The Output pin 7 is the complementary state of pin 6, it is the reverse state or inverted form of pin 6 output.
Now why is a slope shown in the edges, this i have exaggerated a bit so that it can be explained. But then there is a slight slope due to gate input and output capacitance.
In fact if you had a wire or twisted track coming to the input and the R2C1 was in nano seconds, then you would see a ringing at the edges, a tiny peak or spike, which will have giga hertz frequency components, in fact a square way may be many sine waves put together, this you know from a spectrum analyzer.
Two Stage Sequential Timer
CD4538B can give an output with pulse width of 1uS and above. 74HC4538 gives 120nS to 60 Seconds pulses. The above circuit produces a pulse of width T = R3 * C2 after a delay of T = R2 * C1. Some Chips formula is T = 0.7 * R * C .
This circuit is based on a very old application note from exar, in this the frequency is fixed by IC1 and IC2 -P1 controls the duty cycle. you need to compute the R and C values to get what you need, LM555 data sheet.
You have to study the circuit and do something more innovative perhaps, just copying is ok for learning but it will get you nowhere, so learn and then innovate, the eagle circuit is given below so you can learn by editing it, also design a PCB with it, and you can even make a PCB at home to learn, but it is always good to get PCBs done by a PCB vendor, but you should understand his problems, then you will design well, so make a few PCBs.
Edit the circuit eagle cad file del00012.zip