This circuit can be modified using 7555 and switching transistors like BD139 driving a Ferrite 100 kHz transformer to build a Fluorescent Lamp of 10W to 20W.

From Schematics of delabs

Fluorescent lamps can be fired and lit at high frequency at relatively lower voltages. Experiment both with frequency and pulse width to get nominal lighting at good efficiency. One of the reasons CFL lamps -230V and emergency lamps 12V fail, is failure of the switching devices. These have to be overrated thrice or more, the switching heat dissipation should not be underestimated, during low/high voltage and keep a aging allowance.

Designing a working circuit is no big deal. But making a batch of reliable and robust power electronics products, which are idiot proof and abuse resistant is a challenge for engineering. Then they will need it at an affordable price too… Checkmate !

This is also useful as a level detector for colored liquids like oil. This has some immunity to ambient sunlight as it detects ac pulses.

IC 555 is used as an astable oscillator and it flashes the Infra red LED D1 at a high speed, The object close to this LED reflects the light along with the ambient light which may also be sunlight.

IR Led’s and Diodes

The types available are various and polarity hard to detect even photo IR transistors can be used. The IR Led can be tested in diode mode of a DMM (battery should be in good condition) it should give around 1.1V drop in proper polarity. An IR detector diode or photo diode can be tested in the same way the drop will be 0.5V at 1 feet from a 60W lamp (no sunlight), closing the IR photo diode with your hand will be an over range on DMM this will happen on proper polarity. the photo diode shows around 10k ohm resistance in daylight and in Mega ohms when covered also the photo diode detects light on reverse bias and used like that.

This is a three wire voltage to current loop converter. The 1-5 V DC is attenuated and fed to pin 5 LM723 opamp section which tries to maintain the same voltage at pin 10 across the 10 E, thereby producing a open collector constant current sink proportional to the 1-5V input. By trimming the attenuator you can scale-calibrate 1-5V input to 4-20mA output for looping many instruments in series, like a controller, recorder or PLC. With a supply voltage upto 24V, three instruments can be looped. The connection to pin 6 is required to convert 0-1 input to 4-20mA.

This circuit was designed by me in the eighties, the 555 was for negative supply, The whole thing went into the anodized cast aluminuim head of a sensor.

• LM723 Voltage Regulator
• ePanorama Current Loop
• Wiring 4-20mA Instruments
• How 4-20mA Works

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.

The bottom part of the Circuit is the CD4093 Schmitt nand based flipflop. This is my favorite because of studying designs in Elektor Electronics.

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.

• Schmitt Trigger Applications
• Schmitt Trigger 1
• Schmitt Trigger 2
• Schmitt trigger – Wikipedi
• German Schmitt.

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.

• 555 and 556 Timer Circuits
• Discover Circuits – One Shot / Monostable Circuits
• The 555 Timer

The 555 output is fed to clock input of 4040, the output of 555 will be a square wave, on every high to low transition (falling edge or negative transition) the counter increments by one and the output is 12 bit binary.

If input frequency is F the final output at Q12 is F/4096. The period T = 1/F.
If you make the 555 run at 1Hz, C3 around 7uF, Then this circuit becomes a long duration timer, the Q12 period will be 4096 seconds or 68 minutes.

LM555 pdf datasheet.

These are the formulae used by 555 .

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.

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.

• Datasheet of LM555 here pdf
• More about 555 at Educypedia Timers

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