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+5 to -5 using a 555 Astable Multivibrator

This is a very simple -5V supply using one 555, useful for analog blocks using FET Opamps using low power. This circuit came up when i had to design limited by inventory. It worked well for its need. It converts Positive Five Volts to Negative Five Volts to create a dual supply.

+5 to -5 using a 555 Astable Multivibrator

This +5 to -5 using a 555 Astable Multivibrator.is not a high efficiency design, in fact it cannot take a heavy load. Circuits having some CMOS Opamps and a A/D convertor is ok. Even very small battery designs must avoid this circuit.

Home Made Circuits

This suits well when you want to power an analog amp which has to measure voltages which swing on either sides of zero. It can be used in a LCD based portable measuring instrument running on a rechargeable 9V battery.

Powering a strain gauge amp may be one use, another may be like a RTD temperature meter for -50 to +150 deg C.

Thermocouple Amplifier Standard

Thermocouple is the most common sensor in Industrial Temperature Measurement. The Signal Conditioning involves Cold Junction Compensation and High Gain DC Amplification. The output of a Themocouple is in millivolts.

The OP07 is a low offset 75uV opamp, here it is used to amplify the output of a Thermocouple, the gain of this stage is high. The zeners are to protect any high voltage at input zapping the opamp.

Thermocouple Amplifier Standard

The Resistor R6 limits the current. The zeners should be low leakage or use clamping pull-up and pull-down diodes to +5 and -5 respectively.

The RC low-pass filter formed by R6 and C2 reduce the mains hum or 50 Hz pickup of long thermocouple cables laid close to high current heater wiring. R1 is a offset null use or add if required. R11 is gain control of OP07. The TL072 is a FET input opamp used here as a summing amp.

Blind Dial Proportional Temperature Controller

Adding one more inverting amp with some gain to the output of this circuit can give you a 1-5V suitable for ADC or PC analog I/O cards. C1 also serves to filter, it is an integrator here. It suppresses EMI and RFI from motors, contacters etc., R13 sets an output value for 0mV input.

Voltage to Current Source 4-20 mA

The 0-1V to 4-20 mA Converter published earlier is a current sink, Here is a circuit that is a voltage to current converter but with a current source.

Voltage to Current Source 4-20 mA

You can use a LM358 or LM324. The first opamp is a Voltage to Current with a sink output. That current creates a varying voltage w.r.t the 12V DC supply, this varying voltage is mirrored by the second opamp across the source output resistor. This way a constant current is obtained with a sourcing output. The control elements are small signal high gain transistors. Any suitable equivalent can be used. Even the opamp can be chosen by the precision and application you want.

In this form of feedback. way to understand …. “Op-Amp drives the output to maintain both inputs at the same level” and also the “Output takes the polarity of the dominant input” and lastly “dominant means, more positive”. +5 is more Dominant than +3 or 0 or -2. Then -3 is more dominant than -12. See which is more positive.

Long distance of current loop may need higher voltage and lower source resistor value. Then the output transistor needs to change, if you use 24V DC then that voltage should not reach opamp. Design needs to foresee all possibilities of I/O troubles, as these are wired by a customer, mistakes happen. Hence, Industrial Designs have to be rugged.

Solid State Relay – Common

This is a DC controlled Solid State Relay which can turn 230V AC equipment on and off. The output is like a NO normally open contacts of a relay and have to be in series with the Load like any other switch.

Solid State Relay - Common
This should not be used for large inductive loads like big motors. The Q1 transistor limits the current thru the LED by providing an alternate path for more current. The DC input can be from 3V to 20V.

The Triac can be chosen depending on current in the load. Look for datasheets and applications at STMicroelectronics for BTA41600 triacs. MOC3041 zero crossover opto-diacs.

Read more at my main page – Solid State Relays – SSR I used to make them long ago.

Solid State Relay - Common

555 based Reset Generator

You must have read all the circuits and explanation on the other pages at delabs to understand this, as i cannot repeat the same thing as i have done it more than once already.

The circuit is a 555 monostable, The push-switch is to trigger and generate a reset pulse for uC. The diode is for OR’ ing later. The High will go thru the diode but the Low of 555 cannot drink any current as diode blocks.

555 based Reset Generator

The bottom part of the Circuit is the CD4093 Schmitt nand based flipflop. See more at 555 Timer based Circuits

What is the Schmitt then ?, It is better to visit the links below to learn. It can make a sine or triangle or any shape waveform to square. It can help square a very messy waveform.

Two nand gates are connected to form a flip-flop toggle switch. When 555 gives out a pulse, the pulse is delayed by a R-C which results in a ramp, the third nand-Schmitt gives out delayed low trigger to toggle nand-flipflop-switch. The Nand-toggle-switch is rest at any time with the lower pushbutton. The fourth nand output gate is not really required. But the 4093 is quad nand, so unused nand inputs should not float , pull-up or pull-down. So it has just been added in circuit so that he can fit some role, or else he will be bored.

Now you can figure out how such blocks can be used like Lego blocks in your own amazing designs.

0-1V to 4-20 mA Converter

This two opamp circuit converts analog voltage signals to current (sink) signals in a proportional manner. Current signals are more immune to noise and cross talk, hence long wires can be used. Voltage Signal to Current Signal Analog Converter.

Ensure +5/-5 dual supply for chip TL062 IC3. Gnd is common ps ground, let grounds radiate from ground plane in one side of PCB. R3-R8 is an attenuator that may need to be designed or modified.

0-1V to 4-20 mA Converter

In output R23 is for protection from shorting of +5V supply, R23 can also go to an unregulated or external. supply upto 24V DC which is referenced to this circuits gnd. More voltage more distance.

Q2 is the current control device, and R22 50E is the shunt for taking a sample of current. 4-20mA in the output (provided suitable load is connected) means 200mV- 1000mV across 50E shunt. This is fed to close loop control system of IC3a inverting pin.

An opamp on this type of feedback tries to drive the output in such a way, so as to maintain both the inputs at same level.

Mini RTD Pt-100 Three Wire Transmitter

If there is 1V at pin 3 and no current is flowing pin 2 is at 0V so output goes positive and drives Q2. this results in a flow of current till a 1V builds across shunt, if it exceeds then output of opamp falls This reduces drive to transistor and hence current reduces. That is the part of V to I conversion with open collector output.

Now we need 200mV to 1000mV to get 4-20mA 4mA is good for 0 as low level measurements are more noise prone. that is the reason 4mA and not 0mA.

Now we need to convert 0-2 V to 0.2 – 1.0 V using IC3B. R14 is a representation of that 200mV offset set by R16 pot. the opamp IC3B adds both the input and this offset to get 200mV to 1000mV. for that the opamp IC3B is an analog computer, summer, subtracter. Try to now calculate the values for that.

Astable Multivibrator with 555 Timer

This is a demo of the popular 555 timer. you can try out the project on this page by a javascript simulation. Press the Red button below to turn on the circuit press it again to turn off. The 555 can source (LED2) or Sink (LED1) upto 200mA. It can even drive a small motor or lamp with diodes added to protect from inductive kickback.Vary Ra, Rb and Ct with the controls given and see the change of frequency, period and duty cycle.

This is a tutorial with calculator to help learn the application of 555 which is a very rare chip innovation. It is simple, versatile, flexible and programmable (by tweaking of pots).

Astable 555 Timer Flasher – Interactive demo

The 555 Astable oscillator gives a square wave output at pin 3, The output drives two LEDs, LED1 lights up when pin 3 is low and LED2 when pin 3 is high.

The 555 can source (LED2) or Sink (LED1) upto 200mA. It can even drive a small motor or lamp with diodes added to protect from inductive kickback. Vary Ra, Rb and Ct and see the change of frequency, period and duty cycle.

Astable Multivibrator with 555 Timer

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