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Water Level Controller with Reed Sensor

This is a way by which you can monitor the level of fluids like water in a tank. Based on data from the sensor you can control things like solenoids or motors as required or even turn on a buzzer, hooter or annunciator in a control panel. A simple Water Level Controller.


Look at the picture on the right, the float can be a Styrofoam type with a couple of ceramic magnets stuck inside. The float must move freely up and down a long plastic pipe of around 10 mm dia. If the fluid is not water but a solvent then design a non-soluble float or coat the float you made with something like an epoxy resin.

Water Level Controller

Then you need to assemble a small circuit within the long plastic pipe. Many reed relays with a chain of resistors in series has to be inserted in the pipe. The resistor and the glass reed relays should be in different levels of the pipe where you need an alarm or indication. Seal the pipe hermetically at both ends with epoxy resin after taking out a shielded cable of just 2 wires + 1 ground shield.

When the fluid level changes, the float moves up or down with it, when the float moves over a section of pipe where the reed relay is mounted, the magnets on the float make the reed operate and the resistance of the sensor changes.

The resistance is measured and the alarm can be operated as you like. The advantage of this arrangement is the electric circuit does not come in contact with the fluid, no sparking risk.

Reed Relay. It was invented by Dr. W. B. Ellwood at Bell Labs in 1936. Contacts are in a sealed glass tube filled with inert gas like in a bulb, so they do not corrode. It is faster than regular relays and as no spring is used it has a longer mechanical life. The two contacts are ferromagnetic blades plated with rhodium. When you take a magnet close by, the contacts touch each other. You can also put the reed in a coil, then when you energize the coil the reed operates. Used in telecommunication.OKI is one manufacturer of this type of component.

Design and Caution.

When you drive inductive loads you have to use RC snubbers, freewheeling diodes, varistors or zeners. when you drive lamps the cold current is high so use thermistors. The Reed relay is best used in telecom and instrumentation and avoided in power electronics. It can handle high RF frequency as the path of current is straight and footprint small.

Here is a Circuit to Build and Learn this Concepts – This can help make a Water level controller from sump to overhead tank. This can also be used in industrial fluid level control like oils and thick fluids. It may not work with highly viscous fluids or sticky mixes.

Fluid or Water Level with Reed Relays

“When you use the DMM or digital multimeter, try not to use it for high voltages and currents, use external shunts and attenuators instead. If you try to measure 230V AC in the Ohms mode or in the Current mode with the probe in the current socket then you will see fumes in your DMM and a hole in your pocket !!”

– Solderman Talks 1702

Wenzel Associates Technical Library

Since 1978, Wenzel Associates has defined the state-of-the-art in ultra-low phase noise while providing system manufactures with the highest quality, cost effective frequency components and instruments.

Wenzel Associates introduced the Blue Tops system building blocks to offer oscillator users well-characterized, low noise components, which improved the time to market for new frequency based systems.

Wenzel Associates Technical Library

  • Time and Frequency Circuits and Articles including frequency synthesis and conversion.
  • Crystal Oscillator Tutorial Articles cover oscillator types, terminology, and selection.
  • Spreadsheets/ Programs to calculate pll response, phase noise under vibration, and others

Phase Noise Measurement

Wenzel Associates Technical Library

“The measurement technique compares the phase of an oscillator under test to a reference oscillator with similar or superior noise performance.”

Wenzel Associates, Inc
2215 Kramer Lane, Austin, TX 78758, USA

Dual-Low-Noise JFET Opamp TL072 TI

The JFET-input operational amplifiers in the TL07x series are designed as low-noise versions of the TL08x series amplifiers with low input bias and offset currents and fast slew rate.

Quadrature Oscillator – 100 kHz – TL072-TI – TL072-TI  Opamp

TL072-Quadrature Oscillator.png

The low harmonic distortion and low noise make the TL07x series ideally suited for high-fidelity and audio preamplifier applications. Each amplifier features JFET inputs (for high input impedance) coupled with bipolar output stages integrated on a single monolithic chip.


Low Power Consumption
Low Input Bias and Offset Currents
Low Noise
High Input Impedance JFET Input Stage
High Slew Rate – 13 V/µs Typ
Common-Mode Input Voltage Range Includes VCC+

Two Stage Sequential Timer Docs

The circuit is a two stage sequential timer with auto reset. It can turn a Solenoid On/Off after a Sequence of delays that are preset. This is also a basic example of timer usage in automation.

Design Documents

Source Files Orcad Format

All Timers are 1 – 30 Secs Analog with Presets to adjust with a screwdriver. The Switch, Solenoids and Power supply has to be via terminal blocks or plug-jacks. The PCB may be upto six Square Inches for standard DIP components but with SMD it may be smaller.

Block Diagram :

Sequential Timer Specs

The PCB has to be tested to conform with the circuit, this has to be Meticulous. The Circuit is for the Battery and Solenoid Specified and will have to be modified if battery and solenoid are different. D1 to D4 can be replaced by a 300V 3A Bridge Rectifier Module. F1 fuse could be 2A – 3A Slow Blow depends on Solenoid inrush current. Presets can be with some graduations if possible for ease of adjustments. LED resistors can be a bit lower if more brightness is required.

Embedded Microcontroller – delabs

Analog devices like transistors and diodes lead to opamps and analog computing. This takes more parts but with fast devices can be real time. Then came Logic and Digital Circuits, here also big systems will take too many parts. A very Old hp Logic Analyzer instrument, could be HP1607A, had more than five large PCBs, Toggle Switches and numerous 74Fxx TTL Chips. I tried to revive it, it could not be fully restored.

Embedded Microcontroller – delabs

Then came the solution the Microprocessor. Here the entire system goes into the firmware and a Hardware Tool Set in the Microprocessor made up of Logic and Math is sequentially used to perform the same operation that would require innumerable Gates in a plain hardware digital circuit. But as it performs the operations one after another, it takes time and is defined by the CPU Clock Speed.

Embedded Microcontroller - delabs

When the External RAM and EPROM and other peripheral devices moved into the main package, MicroController were born. When more external devices merged with the MicroController. It formed a nearly complete computer, this is known as the SOC.

gEDA Project – Open Source EDA

The gEDA project is working on producing a full GPL’d suite of Electronic Design Automation tools. These tools are used for electrical circuit design, schematic capture, simulation, prototyping, and production.

gEDA – Electronic Design Automation

Currently, the gEDA project offers a mature suite of free software applications for electronics design, including schematic capture, attribute management, bill of materials (BOM) generation, netlisting into over 20 netlist formats, analog and digital simulation, and printed circuit board (PCB) layout.

gEDA Project’s Homepage

gEDA - Electronic Design Automation

gschem is the schematic capture program/tool which is part of gEDA. Its sole purpose is to facilitate the graphical input of components/circuits.

PCB is an interactive printed circuit board editor. PCB offers high end features such as an autorouter and trace optimizer which can tremendously reduce layout time. For custom requirements,


Icarus Verilog is a Verilog simulation and synthesis tool. It operates as a compiler, compiling source code written in Verilog (IEEE-1364) into some target format. For batch simulation, the compiler can generate an intermediate form called vvp assembly.

GTKWave is a fully featured GTK+ based waveform viewer. GTKWave is designed to handle many signals at once, it has three signal searching modes (Regular Expressions, Hierarchy, and Tree) as well as the ability to display data in many different formats.