delabs (Page 3)

Product Design - Industrial Automation and Instrumentation. -

This Circuit helps in the monitoring of mains supply voltage. It does not use a isolation step down transformer. This has to be constructed only by skilled people with knowledge of safety requirements.

C1 limits the current and drops most of the voltage. The zener regulated supply is for the chip. C2 can be raised to 220uF or more if required. The bar mode display may consume more power.

Mains Voltage Power Transformers 

R2-R3-R5-R6 form a voltage divider to get a sample of the input voltage, D11-C3 get the DC value.

Adjust R5 preset with a log Plastic tweaker to get the 5th led to just turn on when input voltage is at 138V AC. This has to be done after PCB is put in a sealed fire-retardant-plastic or epoxy box. drill a hole in box for plastic tweaker.

National LM3914 – Dot Bar Display Driver
This Circuit is Not a Tested Design. It is an Idea for study

Mains Voltage monitor using LM3914

Warning : This Circuit is Mains Operated without Isolation Transformer and will give lethal electric shock if touched when the circuit is turned on. Test circuit only with DC 9V Bench Power Supply to try it out. Do not use 230V AC.

This is a Digital Panel Meter based on ICL7107. This was the workhorse Digital Readout chip before Low power uC designs were developed. Even now it is the easiest way an analog parameter can be displayed in an instrument.

Instrumentation and Measurement Circuits

3-1/2 Display is just enough resolution for recording process data or troubleshooting equipment. With 4-1/2 you notice the problems of thermoelectric EMF of probes and connectors. That is one reason gold plating is used another being low contact resistance. In 4 1/2 the reading can change due to contact resistance too, if the input impedance of the analog signal conditioning is low or the protection diodes, RC filter caps are leaky.

ICL7107 DPM When you measure an analog parameter from a sensor; you attenuate or amplify it, to scale to the A/D converter range. You also need to protect or isolate the analog front end from high energy mis-connections, which will happen during field use. The operator should not get injured from any high energy leakage while measuring.

Resolution is the finest detail you can enumerate in a parameter or object. You can say the crowd was 3000 or 4000 people. Here 1000 is the resolution, finer data does not matter here. You would also hear things like, there were 80 to 90 boys in that classroom. 10 is the resolution there.

Accuracy is how precise a statement or number is. If there was 85 boys in that class, the above statement is accurate. If there was 65 boys, the measuring method or process needs calibration or examination.

In this circuit, the plastic caps should be of very low leakage. Multilayer plastic caps are good for instrumentation.

This is a Constant Current Source LED Driver, When the LED driver Upper-NPN is driven by a voltage thru 4.7K the LED lights up. Assume that the Lower-NPN at bottom is absent. The current via LED and NPN is limited by R. 20mA may be ok 15mA even better. Or LED blows even transistor goes.

LED Voltage Level Indicator

BC547 is like 100mA-40V-200b, Limit collector current to 60mA, use it at less than 25V and depending on the individual transistor you may get a DC current amplification of 200 times. That is 1uA of base-emitter current could give a whooping 200uA of collector-emitter current.

Constant Current Source LED Drive

Still Thinking we do not have the Lower-NPN we calculate the resistor. Vcc – ( 2 LEDs * 1.7) – Vce = Vr that is the voltage across the resistor. You know ohms law and the current needs to be 15mA for a bright and long lasting LED. Lastly 1.7 the forward drop of a green LED and 0.6 a saturated or Turrned-On NPN Vce.

Mains Voltage Current LED Indicators

Now you use the Lower-NPN, The above calculations do not hold anymore. Let us think a small current is flowing in the LED. Then the voltage across R is less than 0.7V, that means base-emitter diode of the Lower-NPN will not get to conduct. The Collector does not draw any current away. Now think that more current flows in LED, the voltage across R builds up above 0.7V the Lower-NPN is biased. The collector of Lower-NPN starts drinking current from the base of the Upper-NPN. So The Upper-NPN starts losing its bias. This lowers the LED current and contains, regulates or controls the LED current as shown in the formula.

This is an electronic choke for a Conventional Fluorescent Lamp. This was an application note of MJE13005 a High Voltage Switching NPN Power Transistor. I Might have modified it. This was very popular in the early days, The Coil Winding and Ferrite is very Critical design.

Emergency Light with Fluorescent Tubes

Tubelight Electronic Choke

The diodes, npn transistor and caps are high voltage 350V-1KV, The tubelight is 40W-60W 5 feet long. This circuit replaced the choke and starter in an existing frame.

Low Cost Simple CFL lamp

Read More.

This is a R-2R Digital to Analog Converter, It converts a byte (8 bit) to a analog value. It has 256 levels including zero.

This was the first Digital Pot i Built decades back – Digital Potentiometer

This can be used to convert a byte sent from a microcontroller to a analog value like say 1.51 V. At full scale, when all 8 bits are high calibrate to give 2.55 V then ever bit increment is 0.01V, 10mV steps.

Digital to Analog with R2R Ladder Network

If the eight bits inputs are from a counter you then will see a staircase waveform at output, each step being 10mV higher or lower depending on whether the counter is counting up or down.

The accuracy of the analog output depends on the resistor ladder. The OP07 has an offset error of about 70uV only. The 74HCT373 power is derived from LM336 a stable reference so that the D-A is accurate. The 8 bit data can be latched with the 74HCT373 to get a stable analog value for control systems.

See another circuit in which both these ICs are used Mini RTD Pt-100 Three Wire Transmitter

OP07E has very low input offset voltage 75 µV max and low input bias current ±4 nA

This will monitor telephone status without loading the telephone line, this way if you have two phones in parallel you will know if one of them is busy. Connect the two ends of circuit in parallel to phone lines.

Telephone LED status indicator

D1 to D4 make a bridge so that LED’s are powered in correct polarity. LED1 indicates line ok no broken line, LED3 can light only when a 12V Zener breaksdown, this shows if line is busy or free, so that you dont go online when someone is talking on the phone in another room. LED2 lights on an incoming call ringing signal.

Learn on Gadget Hacks and Making Things

This is a higher voltage at least in older exchanges, so the cap protects the LED, and LED Lights when a AC ringing signal occurs. D6 protects LED2 from reverse polarity.

Learning Science to Promote Scientific Thinking

Science is best learnt with practical lab work in tandem with theory. Theory becomes appetizing only with practical experiments. In fact theory should follow practical experiments.

ICL8038 and XR-2206 can help you build a Function Generator or Wavform Generator. It is needed along with the Oscilloscope and Power Supply on the Workbench.

The ICL8038 waveform generator is a monolithic integrated circuit capable of producing high accuracy sine, square, triangular, sawtooth and pulse waveforms with a minimum of external components. The frequency (or repetition rate) can be selected externally from 0.001Hz to more than 300kHz using either resistors or capacitors, and frequency modulation and sweeping can be accomplished with an external voltage.

See the Full page with parts list at my Website – Function Generator using ICL8038.

Function Generator using ICL8038

Specifications

Frequency range – 0.95 Hz to 105 KHz in five decade ranges
Waveforms – Sine, Triangular and Square.
Output amplitude – Adjustable from 10 mV PP. to 10 V PP
Output impedance – 50 ohms.

This circuit is a standard way of driving Small Power Relays from Control Signals generated by Logic or Opamp Circuits.

C2 and R5 form a snubber which improves the life of the metal contacts, the contacts can erode due to sparking when switching inductive or even big loads. reduces EMI_RFI.

Basics of Electronics

The Electromagnetic Solenoid Coil is rated by Volts and Ohms. If you choose 12V ensure a stable 12V is provided, more voltage will heat coil, less voltage will cause sparking or will drop out the magnetic holding. A high coil resistance is better as the heat will be less and power consumption of your design is low.

Basic Relay or Solenoid Driver

Q2 is any 500mA-50V-NPN device. For a relay drawing 100mA-12V use a 200mA-50V device or better. D1 is a freewheeling diode, inductive kickback diode or snubber or something that stops the coil from zapping the Q2. Q1 and Q2 form a Darlington pair to amplify the low current drive of some CMOS gates.

Infrared Optical Proximity Switch

R2 and R1 is to hold the bases to ground and avoid floating or else they will pick up noise and relay will chatter….. the contacts will spark ……. the motor or heater will fail to work well……… and your product will get rejected ……….. the payments will be held up …… the customer may even ……………………… stop that right now !

R3 and C1 is a dampener for the signal so that quick relay operations can be avoided, this is important if your relay is driving a three phase contactor which runs a huge Motor. C1 can be increased if required. When huge loads are switched on-off in a factory, lots of spikes and drop outs will reset timer and logic circuits, this will turn on off above relay … leading to the load switched by this circuit going on-off. This may even lead to a Oscillation with the spikes as feedback which can cause great trouble during the troubleshooting process. R4 limits current.