This is a R-2R Digital to Analog Converter, It converts a byte (8 bit) to a analog value. It has 256 levels including zero.

This was the first Digital Pot i Built decades back – Digital Potentiometer

This can be used to convert a byte sent from a microcontroller to a analog value like say 1.51 V. At full scale, when all 8 bits are high calibrate to give 2.55 V then ever bit increment is 0.01V, 10mV steps.

Digital to Analog with R2R Ladder Network

If the eight bits inputs are from a counter you then will see a staircase waveform at output, each step being 10mV higher or lower depending on whether the counter is counting up or down.

The accuracy of the analog output depends on the resistor ladder. The OP07 has an offset error of about 70uV only. The 74HCT373 power is derived from LM336 a stable reference so that the D-A is accurate. The 8 bit data can be latched with the 74HCT373 to get a stable analog value for control systems.

See another circuit in which both these ICs are used Mini RTD Pt-100 Three Wire Transmitter

OP07E has very low input offset voltage 75 µV max and low input bias current ±4 nA

This will monitor telephone status without loading the telephone line, this way if you have two phones in parallel you will know if one of them is busy. Connect the two ends of circuit in parallel to phone lines.

Telephone LED status indicator

D1 to D4 make a bridge so that LED’s are powered in correct polarity. LED1 indicates line ok no broken line, LED3 can light only when a 12V Zener breaksdown, this shows if line is busy or free, so that you dont go online when someone is talking on the phone in another room. LED2 lights on an incoming call ringing signal.

Learn on Gadget Hacks and Making Things

This is a higher voltage at least in older exchanges, so the cap protects the LED, and LED Lights when a AC ringing signal occurs. D6 protects LED2 from reverse polarity.

Learning Science to Promote Scientific Thinking

Science is best learnt with practical lab work in tandem with theory. Theory becomes appetizing only with practical experiments. In fact theory should follow practical experiments.

ICL8038 and XR-2206 can help you build a Function Generator or Wavform Generator. It is needed along with the Oscilloscope and Power Supply on the Workbench.

The ICL8038 waveform generator is a monolithic integrated circuit capable of producing high accuracy sine, square, triangular, sawtooth and pulse waveforms with a minimum of external components. The frequency (or repetition rate) can be selected externally from 0.001Hz to more than 300kHz using either resistors or capacitors, and frequency modulation and sweeping can be accomplished with an external voltage.

See the Full page with parts list at my Website – Function Generator using ICL8038.

Function Generator using ICL8038


Frequency range – 0.95 Hz to 105 KHz in five decade ranges
Waveforms – Sine, Triangular and Square.
Output amplitude – Adjustable from 10 mV PP. to 10 V PP
Output impedance – 50 ohms.

This circuit is a standard way of driving Small Power Relays from Control Signals generated by Logic or Opamp Circuits.

C2 and R5 form a snubber which improves the life of the metal contacts, the contacts can erode due to sparking when switching inductive or even big loads. reduces EMI_RFI.

Basics of Electronics

The Electromagnetic Solenoid Coil is rated by Volts and Ohms. If you choose 12V ensure a stable 12V is provided, more voltage will heat coil, less voltage will cause sparking or will drop out the magnetic holding. A high coil resistance is better as the heat will be less and power consumption of your design is low.

Basic Relay or Solenoid Driver

Q2 is any 500mA-50V-NPN device. For a relay drawing 100mA-12V use a 200mA-50V device or better. D1 is a freewheeling diode, inductive kickback diode or snubber or something that stops the coil from zapping the Q2. Q1 and Q2 form a Darlington pair to amplify the low current drive of some CMOS gates.

Infrared Optical Proximity Switch

R2 and R1 is to hold the bases to ground and avoid floating or else they will pick up noise and relay will chatter….. the contacts will spark ……. the motor or heater will fail to work well……… and your product will get rejected ……….. the payments will be held up …… the customer may even ……………………… stop that right now !

R3 and C1 is a dampener for the signal so that quick relay operations can be avoided, this is important if your relay is driving a three phase contactor which runs a huge Motor. C1 can be increased if required. When huge loads are switched on-off in a factory, lots of spikes and drop outs will reset timer and logic circuits, this will turn on off above relay … leading to the load switched by this circuit going on-off. This may even lead to a Oscillation with the spikes as feedback which can cause great trouble during the troubleshooting process. R4 limits current.

The gain of U1 can be controlled by a digital binary 1248 nibble at ABC. The gain at digital 000 is unity or 1 and the gain at various stages are set by 4051.

Precision Attenuator with Digital Control – delabs

There are eight different gains as the steps of gain resistor network is chosen by 4051. The on resistance of 4051 channel around 100E gets added to U1 pin 2 internal impedance.

Digital gain control of Opamp

Auto ranging 4-1/2 Digit Digital Voltmeter – delabs

You can use separate resistor networks with trimpots for each channel if you require but keep the networks total burden on U1 pin 6 to around 10K, not less than than. You can use this to set the gain of a amplifier with the help of a microcontroller.

This circuit changes the gain of opamp U1B in four steps or segments. It can be used to get a linear output from most transducers to 1% levels.U1A is a amplifying buffer use it to boost the signal to the required level.
Linearizing Circuit for Thermocouples

The resistor values i have put are for an imaginary transducer, you have to design them. The buffered input signal is compared to reference switching points by LM339.

Temperature Measurement and Control

LM339 changes the gain resistors of U1B thru the mux switch 4066. JP1 to JP4 can select either amplification or attenuation of signal. The resistor switched by 4066 can be across R1 or R2 based on JP1 to JP4.

You may have to input transducer values into a spreadsheet and draw a graph. Then divide the graph into 5 segments and deduce the switch points and gain.

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.