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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Saturday, December 19, 2020

Differential to TTL convertor using LM339

Some outputs are via Dual Differential Line Driver type DS8830. This device will interface with standard TTL systems.

Differential to TTL convertor using LM339

The differential outputs are balanced and are designed to drive long lengths of coaxial cable, strip line, or twisted pair transmission lines with characteristic impedances of 50 ohms to 500 ohms. Differential transmission is superior to single wire transmission in that it nullifies the effects of ground shifts and noise signals which appear as common mode voltages on the transmission line.

Mixed and Interface Circuits

If the signal voltage at the end of the line is found to be of insufficient magnitude then the following circuit may be used (at the recipient equipment end) to boost the levels.

Simple Digital Event Counter

The basic digital circuits are Flip Flop and Counter, both are here. This circuit can be cascaded to make even a 6 digit event counter, even a simple frequency counter can be made. 

Digital Timers, Counters and Clocks

These are best done with microcontrollers today. Then what if you have to design your own microcontroller on a FPGA, so the basics have to be sound, hence you have to know what gates, flip flops and counters are.

Simple Digital Event Counter

See the seven segment display. Inc, Dec, and Set buttons are momentary acting and Clk Button is latching type. The Dip Switch in the also can be set. 

Sunday, December 13, 2020

Simple Millivolt Source for Calibration

This is a modification of a mV Source that can be whipped up easily. You could use a DPM or Multimeter to read the output. The ability of this circuit to perform well depends on the quality of all the MFR resistors and the MultiTurn Pot. Use a Bourns 10T Pot.

Good Soldered Joints, Keep all Resistors and temperature sensitive parts from Transformer and Regulators. Keep Ripple in power supplies low, no EMI tolerated. If you have problems, make a Battery Powered Unit. Shield well in case you are in a Electrically Noisy environment.

Millivolt Source In this link see at bottom this circuit millivolt source, pdf.

Simple Millivolt Source for Calibration


I have put a better offset null, OP07 has around 75uV offset error which may show as +/- 1 count error on 4 1/2 DPM 19999 counts. You can skip it if you are using a 3 1/2 digit DPM as the error will not show, even it 4 1/2 it may be upto 2 counts only.

Tuesday, November 03, 2020

Astable Multivibrator with 555 Timer

The 555 Astable oscillator gives a square wave output at pin 3, The output drives two LEDs, LED1 lights up when pin 3 is low and LED2 when pin 3 is high. 

Astable 555 Timer Flasher

 The 555 can source (LED2) or Sink (LED1) upto 200mA. It can even drive a small motor or lamp with diodes added to protect from inductive kickback. Vary Ra, Rb and Ct and see the change of frequency, period and duty cycle.

Astable Multivibrator with 555 Timer  

The max power dissipation of 555 is 700mW so overload of more than 200mA will damage the device, connecting the battery in the reverse or wrong polarity will also damage device, ensure also Ra and Rb do not go less than 2.2K (use 4.7K minimum) as it may damage the discharge transistor at pin 7. The supply voltage can go upto 18V. For CMOS 555 like 7555 see the datasheet they are different.

Running Lights with CD4017

The 555 Astable generates a clock for this circuit, an oscillator giving a square wave output at pin 3 which is counted by 4017 to give a running lights effect. 

Running Lights with 555 and CD4017

The decade counter-divider CD4017 has 10 outputs, for every low to high transition at the clock input, rising edge, the counter advances one LED. After going one full circle the the first LED lights again and it goes on. You can vary the value of R2 100K Linear potentiometer to make LEDs run fast or slow.
Running Lights with CD4017
The frequency of oscillation of astable 555 is given as f = 1.44 / ((R4 + 2 * (R2 + R3)) * C3)
The 10 outputs have 10 green LEDs. The current thru the LED is limited by R1, the current can be calculated like this (9V - 1.6V) / 1K = 7.4mA this is within 20mA which is the danger limit of the CMOS output. You want it to be bright use transistors for every output. 

Dual Polarity Power Supply

This supply gives both positive and negative outputs. Appropriate Fuses should be used to protect from fire hazard and overload of transformer.

Voltage Regulators LM7812 and LM317

You could use LM7824 or LM7815 or LM7812 for 24V, 15V and 12V respectively. You could use LM7924 or LM7915 or LM7912 for -24V, -15V and -12V respectively.

Dual Polarity Power Supply

The Filter capacitor C1 4700uF has an impedance of Xc = 1 / (2 * 3.14 * f * C) which comes to 0.6 ohms at 50 Hz.

Power Electronic Circuits

The impedance of the load at 2A for 24V is R = V / I that is 12 Ohms which is more than 20 times the impedance of the capacitor at 50 Hz. That means less than 1 / 20 of ripple current will flow thru the load. The Regulator also reduces the ripple a little.

Saturday, October 10, 2020

Current Amp digital control - DMM Project

R6 is the Shunt thru which the current to be measured passes. F1 fuse is to protect shunt. D1-D4 ensures that the current flow is not broken if the shunt blows. The Ammeter is always used in series in a circuit.

 Current Shunt Amplifier with digital control - del20014 

OP07 is used here as a digitally controlled amplifier as the voltage offset error is around 75uV. 4052's digital controls A-B set the range by selecting R1, R2, R3, R5 for the digital code at A-B. The inverting amplifier changes the gain and four current ranges are got. The output of this circuit has to go to a buffer and cannot be loaded directly. R8 is offset trim at very high gains, it has to be adjusted for a zero output of opamp for zero current measured.

Current Amp digital control - DMM Project
Rf and Ri are 0.1% MFR, if costly, use bourns 10T trimpot or a difficult way - use series parallel combination and scratch 10% part of resistor network to increase value.

Voltage Attenuator Amp - DMM Project

LF356 opamp FET input is in a inverting amplifier configuration here. R4 + R5 make up Ri each 1/4 W MFR withstands 250V so both will take upto 500V. Use more in series for higher voltage withstand with care in PCB layout and cabinet insulation.

Voltage Attenuator Amp - DMM Project

Rf is selected by a digital value at A-B inputs of 4052, that way R1, R2, R3, R6 are selected for four ranges giving various attenuation levels. The important thing in this circuit is the on resistance of 4052 of 100 ohms comes in series with the output resistance of opamp, so the output is taken before the cmos switch . The output of this digital attenuator should not be loaded and should be buffered before use.

Gain = Av = Rf/Ri and Vout = -(Rf/Ri) * Vin

Voltage Attenuator Amp - DMM Project
Rf and Ri are 0.1% MFR, if costly, use bourns 10T trimpot or a difficult way use series parallel combination and scratch 10% part of a network R to increase value.