Showing posts with label Discrete-Circuits-3. Show all posts
Showing posts with label Discrete-Circuits-3. Show all posts

Tuesday, October 04, 2016

RS232 with Opto-Isolation

I had to once interface an high voltage circuit to PC, The uC had to communicate thru RS232--Comm port--Serial Port.

Part of the 80C31 8051 SBC

Even though i had isolation at the sensors and actuators to make doubly sure the PC also has been isolated. There are chips that are available for this purpose, The circuit above is built with discrete and passive components except for the opto 4N35. You can use MCT2E and CNY17-3 Optos too. For MCT2E some tweak may be needed as current transfer ratio is 20, for the other two CTR is 100 so above design will work.
RS232 with Opto-Isolation

The circuit derives power from PC but does not load the PC supply. Any voltage above 5V applied to the PC connectors may lead to damage of motherboard in PC. Old PCs were more vulnerable but PCs today maybe a bit rugged at the Ports. Due to internal current limits and clamping.

The VCC, VDD and Agnd are derived from PC no other power needs to be applied on PC side of opto. On uC side of opto the uC power supply lines +5 and gnd has to be used. There is no copper link between the two sides and depending on opto a 1KV isolation is possible if PCB is well designed. The PCB should show the visual isolation above and components should be laid on separate areas of PCB to prevent creepage.

The LEDs are to indicate the port activity Rx and Tx, they are not required once testing is over. The circuit can be simpler, but this worked for me and it is not tested at very-high buad rates.

The levels of RS232 are not TTL like 0-5 we have both polarities +10 and -10. The circuit has to change that to drive the Opto Leds.

RS232 software. Understanding RS232 Serial Port Communication.

Monday, June 13, 2016

Edison Bulb Life Extender

The Edsion Filament lamp may be less popular, but it is the most cost-effective light even today. It is very affordable, The light is soothing to the eyes and best of all gives a warm feeling.

Edison Bulb Life Extender

Sometimes due to the mains being restored when bulb is on, or a rapid flick of switch, blows it. This may be due to the cold filament resistance which is low, allowing a huge inrush current.

LED Lighting - The Future is Here

The problem can be solved with a soft start based on thyristor or mosfet using PWM etc. The circuit here is a low cost solution which may help a bit in reducing the inrush cold current Protection from long duration high voltages is also required but will make circuit more complex.

Now why would anyone spend for a R-C network for a bulb, you could as well buy a new bulb. But I once got a back sprain while replacing a bulb in a hurry, So the price of the bulb alone is not the issue.

CFL Lamps and Simple Inverter

The two diodes 1A form a AC path with a switching delay of diodes, The R-C network is for soft start. The Varistor-Thermistor has a cold resistance 4.7E which reduces as it warms up. If switch is flicked rapidly or power fluctuates, then varistor cannot help as its response is slow. The 10E resistor ceramic fusible wirewound resistor and C1 does the job of absorbing .

This circuit has not been tested for long times at multiple places, so i am not sure of its performance.

Monday, December 19, 2005

Relay Driver - Electromagnetic

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.

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.

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.

Some complained there are no explanations for the PDF circuits, so i am trying this, so please bear with me.

Circuits by Application

Analog Circuits

  1. Battery Level Indicator
  2. Simple Sample and Hold
  3. Sample and Hold Standby
  4. Voltmeter Attenuator
  5. Precision Current Source
  6. Opamp Supply Virtual Ground

SCR and Triac

  1. Solid State Relay
  2. Normally Closed AC SSR
  3. AC-AC-SSR
  4. DC-DC SSR
  5. 2N2646 based Pulser
  6. Drive SCR thyristor

Mains Power

  1. Flashing Neon Lamp
  2. Dimmer power control
  3. Edison Bulb Life Extend
  4. Mains Current LED
  5. Mains Voltage LED

Digital Circuits

  1. Simple Digital Counter
  2. Running Lights
  3. Frequency Divider
  4. Crystal Oscillator
  5. Simple High speed switch
  6. Differential TTL converter

Measureall DMM

  1. Ohmmeter Measure Resistance
  2. Precision Digital Attenuator
  3. Precision Amplifier

Mixed Circuits

  1. Monostable Multivibrator
  2. Digital to Analog
  3. LM311 Oscillator
  4. PLL using 4046
  5. VCO with LM331
  6. BCD Thumbwheel to Analog
  7. V to F Converter ICL8038
555 Circuits
  1. OR gate with two 555
  2. fixed frequency duty cycle
  3. Pulse width modulation
  4. Astable Multivibrator
  5. uC Reset Generator
  6. LM555 Voltage Doubler
  7. 555 Power Oscillator
Discrete Circuits
  1. Isolated dual supply
  2. Sound to light converter
  3. Water operated relay
  4. Telephone Indicator
  5. Passive volume control
  6. RS232 Opto-Isolation
  7. Voltage Level Indicator
  8. Relay Driver
  9. Constant Current LED
  10. Voltage Doubler
  11. FET Current Source
Opamp Circuits
  1. Three Opamp Differential
  2. Two Opamp Differential
  3. Buffer Opamps
  4. Differential Op-Amp
  5. Inverting Opamp
  6. Non Inverting Opamp
  7. Digital gain control
  8. Square Triangle Oscillator
  9. Dual Polarity Output Amps
  10. Ammeter Precision Rectifier
  11. Voltage / Current 4-20 mA
  12. Current Source for RTD
Power Electronics
  1. Dual Power Supply
  2. Single Power Supply
  3. Battery Backup Supply
  4. 5V 1A Supply LM2575
  5. 5V Power Supply L296
  6. Dual Power Supply
  7. Tubelight Electronic Choke
  8. Voltage Doublers Multipliers
  9. White LED Lamp on Ni-Cd

uC and uP

  1. PC RS232 with MAX232A
  2. Battery Backup SRAM
  3. watchdog uC uP systems
Instrumentation Circuits
  1. Mains monitor LM3914
  2. Simple Mains monitor
  3. single digit voltmeter
  4. High Resistance Meter
  5. Diode Thermometer
  6. Function Generator
  7. Diode Leakage Tester
  8. Analog LED Ohm Meter
  9. Millivolt Source Current Loop
Process Control
  1. AD590 - temperature
  2. Thermocouple Amplifier
  3. Linearizing Thermocouple
  4. Thermocouple Amplifier
  5. 0-1V to 4-20 mA
  6. 1-5V to 4-20 mA
  7. InfraRed - Optical Switch
  8. InfraRed Detector