Schematics of delabs

This circuit is built around the chip CD4067, now called 74HC4067, it works like a single pole 16 throw rotary switch that can be controlled digitally. Clamping protection diodes are built in. Use resistors to enable this protection.


Pan and Zoom the Circuit for detailed Study here - Sixteen Channel Multiplexer

The ON Resistance of this chip is around 100 ohms and OFF resistance may be in Giga ohms. Use  74HC4067 for CMOS periphery. 74HCT4067 for a TTL environment.

16 Analog channels are controlled by a Digital User Interface circuit made of 4093 and 4029. Up/Down and Auto/Man are four Push-buttons. A LED Display to show the Channel Number that is selected.

Mixed and Interface Circuits

The output of the Mux goes to OP07 whose high input impedance and low offset enables an accurate low impedance output that can go to the A/D Convertor, PLC Unit or DPM - Digital Panel Meter or voltmeter.

This circuit has two analog mux 4051 operating in synchrony to store an analog value in a low leakage tantalum capacitor. This makes an Analog Memory possible and overall system accuracy of around 2%, which was more than adequate for this process.

Mixed Circuits Analog with Digital

The analog value from a temperature transmitter is available for a short duration when it is collected from a rotating system with copper brushes and contacts on the shaft.


Pan and Zoom the Circuit for detailed Study here - Synchronized Analog Mux 

The CA3140 with one tera ohm input impedance ensures the accuracy of the analog memory. The scanning by 4029 counter frequently refreshes and updates the analog data.

The 4-20mA signals are converted to voltage by a 50 ohm shunt 1% MFR of 1Watt rating. The clock and reset signals are coming from 12V proximity switches. This is filtered and tamed by a simple transistor circuit. That way the 5V Logic circuit is safe from the 12V external inputs.

Since both the 4051 operate in tandem the analog value in the tantalum capacitor does not discharge through the 50 ohm shunt current receiver.  The CMOS switches offer very high OFF resistance, that makes this circuit workable if properly adapted.

A single Voltmeter or Digital Panel Meter DPM can monitor 8 Analog inputs from sensors or potentiometers using a Mux chip and creating simple digital controls for that.

The Pushbutton Logically Interlocked Controls are Auto and Manual. For Manual Setting Up and Down push-buttons select the channel. In the Auto mode the 4029 counter gets pulses from a 4093 Schmitt Nand Gate wired as an Oscillator. This circuit shown for six channels.

Industrial Process Control Circuits

Four pushbuttons on the front panel control the scanner.  One 4051 is used to multiplex 8 trimpots that hold the Analog Alarm Settings. The channel number in BCD is  translated to a LED channel Display with a 4511 chip.


Pan and Zoom the Circuit for detailed Study here - Digital Control for Mux

The 6 or 8 LEDs decoded by the 4017 are placed just above each Trimpot. Select the channel and tweak the trimpot of the LED that is turned on. The output of U7 OP07 can be measured with a digital voltmeter to monitor the trimpot setting value.

Digital Timers, Counters and Clocks

This way all the channel alarm settings can be trimmed or tweaked by watching the voltmeter while turning it. Carbon or metal film presets should not be used for this. Something like Bourns ten turn trimpot. If changes made are more than ten times a month, you would rather use a bourns ten turn potentiometer.

This is the full circuit of a V/F convertor interface for 80C31 SBC. The Mux is configured for selecting between two inputs. It uses analog switch 4066. LF353 along with LM331 form the VCO, you can further study such configuration in the Application Notes of TI/NS.


This design is built above an application note.  Two Pt-100 RTDs are switched to the A/D using the FET Switches.  Here a 1mA Precision current source is shown at the bottom for RTD and a 50mA Current source is shown above for special uses as an example.

Mixed Circuits Analog with Digital

The Output Fout is a Frequency which is directly proportional to the measured voltage Vin. The pulses can be isolated using opto-couplers to avoid ground loops or electric hazard. An additional protection and scaling circuit at the input may be required for some sensors.

delabs designs - delabs notes

This circuit is alternative approach to same solution show in earlier post. Here i have put the complete circuit in PNG format. 8038 is a marvelous chip, a custom monolithic analog computation unit, a device popular around the 80s, it was far ahead of its times indeed.

Now its availability and application are much reduced. Intersil made Popular Analog ASICs, the word ASIC itself came much later. They were also early in making low power cmos, this was at a period when microprocessor system consumed a lot of power and microcontrollers had just started coming in.
Tacho Counter for Speed and Quantity Measurement

This was a small circuit made for driving an Impact counter. The heart being ICL8038. It must have been a Motor driving a Conveyor, the motor has a feedback attachment called Tachogenerator.


Only part of the circuit is shown here. See the image of product here Tacho Counter. The configuration is derived from the Application Notes of Intersil. The Voltage from Tachogenerator is Measured on a DPM-DVM and also fed to this circuit after attenuation and filtering.

Function Generator using ICL8038.

The square pulses of 8038 is used to derive a Logic pulse train for a CD4040. The CD4040 works of 0 and 12V. The above circuit is on +12 and -12. That is the reason R10-R15-Q1 are used. The pulses are 0-12V pulses. The Zero is Virtual like the Virtual Ground in low current power supplies.

 delabs designs - delabs notes