Digital-Circuits

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

Sample and Hold with Standby CD4053

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.

I don’t remember if this circuit worked properly. But a few were made and i might not have shown the modifications that were done to make it work. This was meant to be a portable, low cost, insulation tester for an electrician. If you try it out and debug it it may work well.

High Resistance Insulation Materials

A negative voltage is derived by shifting gnd with two diodes, i feel this did not work very well. Two pins of CD4028 pins are also used to boost the reference to get two extra ranges as 4051 has a 100E on resistance.

High Resistance Meter

The 555 clock makes 4029 counter count. But the clock can be clamped to gnd by a TL062 window comparator. The clock is frozen when the input value to comparator pin 5-2 is within a lower limit and upper limit “window” pin 3-6.

Insulation Tester

The 4029 counter BCD is decoded to decimal by 4028 which drives the LEDs, keep LED drive within 3mA or chip will be loaded. Use high efficiency extra-bright LEDs.

The 4029 BCD also controls a shunt resistor array with CMOS switches 4051. The voltage across shunt is a sample of leakage current. This is compared in the window comparator to freeze the Clock and LED display to give a reading of the leakage current or Insulation Resistance.

The CD4020BC, CD4060BC are 14-stage ripple carry binary counters, and the CD4040BC is a 12-stage ripple carry binary counter. The counters are advanced one count on the negative transition of each clock pulse. The counters are reset to the zero state by a logical “1” at the reset input independent of clock.

CD4040BC, 12-Stage Ripple Carry Binary Counters
CD4060BC, 14-Stage Ripple Carry Binary Counters

1 Hz or 1 PPS Crystal Clock Base

CD4060 – 14-Stage Ripple Carry Binary Counters

you can also use a crystal between pin 10 and 11 with two caps 22pF from 10, 11 to gnd and a 10M resistor between 10 and 11 in place of R C network for more precision.

74HCU04 is a chip that was made for this purpose, HCT may not work for such a circuit. C1 and C2 can go to upto 33pF and R2 can be increased to make R2 * C2 = t.

Crystal Oscillator - Parallel Resonant

 

Time constant much less than the period T of the crystal T = 1/F . This is to remove higher frequency components in the Oscillator.

More on Piezoelectric Crystal Oscillator

The circuit above is a parallel resonant oscillator circuit. The Crystal works by the piezoelectric principle, piezo means pressure. The electric field causes the impedance of the crystal to change. The LP Record Player needle is the reverse of this, the bumps on the spiral groove of the record applies pressure to needle which generates electricity. Both are piezo-electric effects.

This was a attempt to make a Sequential Timer with ICM7217 of Intersil, even though it worked well, it was not developed beyond the prototype stage or first iteration. Only when a product is made in some numbers, the documentation and designs become clear, streamlined and seasoned.

Timer Circuit

The PCB and Circuit are not complete. It may give ideas. During this time, as far as i can remember, these were the only large CMOS devices. 8080-85 and Z80 devices consumed lot of power and needed big boards and supplies.

ICM7217 4-Digit, Presettable, LED Up/Down Counter Maxim

7217 Timer Counter

Study this, if you are not good at firmware or you need a simple solution, this is still a versatile chip. It is better you make your own PCB. This board can be used for prototyping only.

Timer Circuit pdf

Clock Circuit pdf

The MM5369AA and 3.579545 MHz

I have converted from DOS Orcad to Windows, corrected some mistakes, use with care. Orcad on DOS had a very user friendly interface, it had a near windows like GUI on DOS, when windows did not even exist, It had right mouse button controls too.

This is a Test Circuit for Logic Analyzer software, with the Simple port circuit. The VB Logic Analyzer works, but is just an example program to test and learn.

Printer Port Logic Analyzer

The speed at which the logic state changes say like 10 M Hz while probing even a PIC or 89C51, is too fast for this circuit. For that, the incoming data has to be spooled or stored in RAM at real time, by the external Hardware itself.

Test Circuit for Logic Analyzer software – del20006

As this is a Parallel Port Interface, an Embedded High Speed Digital RAM Storage of Multiple Logic input Channels with Signal Conditioning in the front end, could do the job. This is the minimum, if you want to program the rest of the instrument on Computer Software. Here is one you can see from Bitscope using USB or Ethernet.

Printer Port Circuit to see the inputs logic state and drive a few outputs. The preset control program helps test out the circuit operation. Use safe 5V Levels.

Simple Printer Port Interface, Input-Output – del20005

So i made some example circuits and VB programs for students. A demo Milli Volt source, Digital Voltmeter and Logic Analyzer examples for learning, are on these pages. I have tried to derive power from PC itself in this circuit, Care should be taken not to short circuit or apply any voltages above 5V to PC Port Pins.

Simple Printer Port Interface

74HCT373 is the only chip used to interface the real world with the PC Parallel port. The Inputs to this chip are protected with Resistors and Zeners. 3 outputs of PC are also monitored using LEDs. This gives you a IO interface for experimenting. Below is a Preset counter simulation that you can use with this circuit for testing. Schmitt Triggers and Signal Conditioning may be required for Noisy and Non-Sandard Inputs.