Monday, May 27, 2019

LM331 A to D with Mux Input Switch

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.

LM331 A to D with Mux Input Switch

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

Sunday, May 26, 2019

Tacho Counter usong ICL8038

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.

Tacho Counter usong ICL8038

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

Friday, May 24, 2019

Tacho Generator - VCO using Opamps

The opamp section of VCO was published earlier for better readability. The full Orcad Schematic in PNG format is here. Many an instance, analog solutions are not only cost effective but very reliable if properly manufactured. They are also as Real-Time as real time can be. Hence never give up on analog for small solutions. It can never be substituted in the front end where the device has close encounters with Real World Parameters.

Even if you have a miniature IoT device, there is a analog front end to it and it gets integrated into the chip too. The designers should always understand how to ensure that the analog front end is robust by using proper protection, filtering or isolation when necessary.

Tacho Counter for Speed and Quantity Measurement

The pulses can be used to advance digital counter or mechanical counter using a solenoid driver transistor circuit. The Voltage Vin can be further scaled and fed to a Digital Panel meter to read the rate.


This is a Voltage to pulse converter using opamps for measuring speed or rate from a Tacho Motor mechanical coupled to a Conveyor System.

See the complete circuit in my site to study other sections. The motor DC out is filtered and scaled. Then the clean safe dc is fed to this VCO based on a generic application note design. 

VCO - Voltage Controlled Oscillator using Opamps. LM339 is a quad  Comparator.

The complete PDF circuit and other such circuits at my Mixed Circuits Analog with Digital

delabs designs - delabs notes

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