Ideas of delabs Technologies

A very simple one op-amp diff amp. This amplifies the difference between two inputs Vp and Vn the low impedance of this configuration is a drawback, but can be used in analog computing. Optimum VCC VDD can be +12/-12. AC signals common to Vp and Vn are canceled by this configuration.

Differential Amplifier - Op-Amp Circuits



Use a capacitor like 10nF plastic from pin 2 to 3 or across R2 to make circuit stable. For AC applications use LF351 TLO71 as they have good slew rate and also are FET inputs. For AC applications use a capacitor (1uF) in series with Ri to block DC Components.


The Inputs have asymmetrical input impedance this affects CMRR, also use 1% tolerance MFR resistors for Rf and Ri.

Vout = ( Vp - Vn ) * ( Rf / Ri )

Slide the Potentiometers just like you would operate a Sliding Control. Drag the Knob on Pot to increase or decrease the resistance. The Resistance is shown is blue letters and dynamically alters value as you slide the pot.

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If output impedance of a point is a high value then connecting another circuit at that point will load it, resulting in malfunction or error. Buffers are used as interface between circuits.

Low impedance of an output means it can source/sink lot of current, when you need 2 opamps use LF353 or TL072 which are dual opamps.



Buffer Unity Gain Amp - Op-Amp Designs

A non-inv FET input is the best buffer, for inverting buffer use high R values. Using very high R values like 2.2M or higher requires a glass epoxy PCB and guard rings around pin 2, 3 to prevent leakage currents on the PCB reaching the PINs.

Also moisture and dust has to be prevented by using RTV coating or Varnish. Use 78L05 and 79L05 for the dual supply required by this circuit.

Inverting Amp   -   Vout = -1 * Vin

Non-Inverting Amp   -   Vout = Vin

Vary the Millivolt Source by just hovering your Mouse pointer over the Two Buttons (Increment and Decrement). If you leave the mouse pointer on a button, the variation will pick up speed. Set a Value of your choice, positive or negative, you can set from -199.9mV to +199.9mV. Note the Output values on both the DVMs on the right (digital Volt Meter) in a Table. Repeat this for at-least 7 readings of both polarities. Jot the Formula below in your book and relate it to your table.

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The Input Impedance of this module is very high and is symmetric. This circuit can be used for strain gauges and for four wire measurements. If inputs are in mV use OP07. The merit is that it uses only 2 OpAmps yet has high differential Input Impedance.

Dual Differential Amp - Op-Amp Designs



The Outputs of Opamps are low impedance but still have limits they cannot drive more than a few mA of Current into the Load. If low ohmic value loads are to be applied use external transistors as amplifiers. If inputs Vn-Vp are floating, outputs may be random or oscillating, it is good to have a bias network of 10M resistors to a potential even zero or common, this enables some Vout when input floats.


 Vout = (Vp - Vn) * (Rf + Ri) / Ri

The Variable Resistor or Sliding Potentiometer for Rf and Ri are present for Gain Setting. Slide them to vary Rf and Ri, Assume both Rf values vary in tandem, when you slide the Rf Pot. Like a Ganged Pot or Dual Pot. Even Ri is a Dual Pot that varies both Ri Simultaneously. Now set the mV of Vp and Vn using the mV Sources provided. Just Hover Mouse pointer over buttons, variation ramps up if mouse pointer is left on the buttons. No pressing Buttons here. Take the Vout readings, tabulate the Results.

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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.  If you are starting with electronics, this is the first step. So do it now ! Do-It-Yourself.

Screenshot of Astable 555 Timer Flasher

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.

Screenshot



These are the formulae used by 555 and same is used in javascript without any change.


T1 = 0.693 (Ra + Rb) * Ct charge time of Ct
T2 = 0.693 (Rb * Ct) discharge time of Ct
T = T1 + T 2 total period in seconds
F = 1 / T = 1.44 / ((Ra + (2 * Rb)) * Ct) Frequency in Hertz
D = T 2 / T duty cycle, multiply by 100 to get %.

Ct in farads and Ra-Rb in ohms.

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.

Astable Multivibrator with 555

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)

The max power dissipation of 555 is 700mW so overload of more than 200mA will damage the device, connecting the battery in the reverse or wrong polarity will also damage device, ensure also Ra and Rb do not go less than 2.2K (use 4.7K minimum) as it may damage the discharge transistor at pin 7. The supply voltage can go upto 18V. For CMOS 555 like 7555 see the datasheet they are different.

Vary Ra, Rb and Ct with the controls given and see the change of frequency, period and duty cycle.

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Human Beings are helped or hampered by many types of Microbes. From the Sub-Microbe virus to animal like Bacterium and plant like Fungi.

An Affordable Portable Electronic Microbe Detector using Mass Spectrometry; may be very useful for Small HealthCare Centers and Homes. If a Person Breathes into an adapter in the instrument, it should show a simple analysis of the Air Microbe Levels. It can also be used for CleanRoom Air Purity Indication.



This is just an idea for an urgent need, this may prevent spread of flu to escalate into an epidemic; due to early detection of microbe, at the root, in every home.

Here are some Mass Spectrometry Resources that students can study and attempt to research to Develop a cost-effective consumer flu-detection device.

Ideas of delabs - 2004- First posted in my blog Analytical Bionics.

ideas of delabs - id2002

Learn more about the Subject Basics

• Mass spectrometry (MS) An analytical technique
• American Society for Mass Spectrometry  

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