Schematics of delabs

One of the oldest Schematic Archives on the Web. It was in the form of pdf files in the late 90s. Instrumentation and Industrial Designs by delabs and Generic Application Designs.

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Wednesday, September 16, 2020

DMM range and AC-DC mode Logic

This is the third circuit that you will need to build a Simple Benchtop DMM with no Microcontroller.

Here the U1D and U1B 4093 acts like a de-bouncing circuit for the push keys. The 4029 counts up scrolling to binary values 00, 01, 10, 11 for the four ranges.

The binary value of 4029 is decoded to decimal by 4028 in order to light four LEDs which indicates the range or mode on the front panel. When any of these pushbuttons are pressed and held, the nand schmitt 4093 clocks to scroll the range continuously. The binary output of these counters control CMOS switches 4052 which are analog multiplexers.

DMM range and AC-DC mode Logic

The DPM or DVM gives a readout of an Analog Value or process. The Analog reading we obtain from a Circuit Measurement Jig represents some real world parameter.

In a multi-parameter instrument like DMM, the measurement jig functions and the analog signal routing is done by ganged range selection switches.

Read More here DMM range and AC-DC mode Logic

Isolated dual power supply from 5V

This is a unregulated supply for low power circuits. You may be able to regulate the outputs with zeners or small regulators like 78L05.

The transformer can be hand wound in a mini ferrite pot core. you can use 2N2222 or any other fast transistor. The transformer should have 1KV isolation. The dot polarity of TR1 should be properly observed, else it may fail to oscillate or give output.


Isolated dual power supply from 5V


Diode should be fast recovery type, for less than 100mA use 1N4148. transformer, pri-20-20, sec-60-60, a SWG-AWG to suit the current you

Circuits using only  discrete devices

design for, any fast switching transistor would work, no regulation, use regulators like 78L12 if you want, circuit like multivibrator used for flashing LED lights.

Thursday, September 10, 2020

Crystal Oscillator - Parallel Resonant

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.