Mixed-Circuits

Let us assume you have to Measure Amps and Volts in four independent circuits. This becomes a Multi Channel Voltmeter and Ammeter.

Analog-Multiplexer

This circuit uses a 4052 as a DC  Analog Multiplexer, the inputs to this Mux must be from Low Impedance Output OpAmps. The Resistors Shown are not needed once the Signal Conditioning Opamps are connected. The Restors can be 100K to keep the inputs from floating, that will not load an opamp. The resistors can attenuate signals if  sensors are directly connected.

Instrumentation and Measurement Circuits

The signals from sensors have to be amplified and corrected or scaled before reaching this Switched DVM. For Current a Shunt is the Sensor and for AC current a CT or current transformer is the sensor. Voltmeter has Attenuator as the ‘Sensor’.

The 7107 DPM can be replaced by the Analog Inputs of the Arduino or Microcontrooler A/D Stage.

This is the continuation of the earlier post. Part of 80C39 based Process Controller. In this schematic you can see the Watchdog and D/A Converter.

80C39 and MCS48 based Process Controller is the main circuit that has the LED 7 segment display for output and push keys for input. The old form of Human Machine Interface – HMI.

Digital to Analog Converter with uC Watchdog

My first observation of a very complex watchdog in action was an Agilent(hp) Benchtop Multimeter based on this 8048 family of 1st generation microcontrollers that did not even have a UART among many things.

At that time CMOS was just making an entry and FLASH memory was unheard of. The UV Eprom was the way firmware was set on these systems. These consumed a lot of power. 80C39 was the CMOS one.

The  4040 counter derives a slow clock from the 7555 timer. The counter has to be reset by firmware by periodically sending a reset pulse on port pin P2.7 to say “Alls Well”.

If the firmware or uC “hangs” or due to EMI or Spikes the uC gets into an endless loop. Then the “Alls Well” pulses stop coming. The 4040 keeps counting till Q10 output goes high and resets the uC or can we say Wakes it up rudely.

The D/A converter was used to get the 1-5 V to obtain 4-20 mA control Signal to operate the Actuators like a Motor Drive or Heaters in a Industrial Process control System.

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

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

Specifications

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.