RS232 with Opto-Isolation

 Digital-Circuits, Discrete-Circuits, Embedded-Systems  No Responses »
Sep 262005
 
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. 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. The circuit derives Read More …

 Posted by admin at 5:37 AM

LED Voltage Level Indicator

 Discrete-Circuits, LED-Circuits  No Responses »
Jul 302005
 
LED Voltage Level Indicator

This circuit is derived from a Siemens Application Note 1974. This circuit uses common components of today. The circuit is here as it is of high educational value. I have not tested it. You can ‘simulate and test’ or ‘wire it up and try’ and let me know how it worked. The Circuit is also a simple analog to digital converter. You can use optos in place of LEDs. T1 and T2 make a differential amplifier. T3, T4 and T5 driving the LEDs are comparators. Now to learn more on how they work you have to study circuits at 4QD-TEC Read More …

 Posted by admin at 9:05 AM

Simple High speed data switch

 Digital-Circuits, Discrete-Circuits  No Responses »
May 162005
 
Simple High speed data switch

This circuit is a small representation of a very low cost printer sharer i made very long ago. This is as much i can remember of the basic ideas behind the product. I used to pot the product in epoxy with a black dye and sold a few, they sort of served the purpose. Output impedance of this circuit is high, sink is 220K source is 3.9K+ so use some buffers or drivers at Output. when Enable A is at float-high impedance or low the output O1-O4 is not influenced by A1-A4 inputs. If Enable A is made logic high Read More …

 Posted by admin at 6:01 PM

Edison Bulb Life Extender

 Discrete-Circuits, Mains-Power  No Responses »
May 022005
 
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. 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. 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 Read More …

 Posted by admin at 8:06 PM

Passive volume control with Potentiometer

 Discrete-Circuits  No Responses »
Apr 212005
 
Passive volume control with Potentiometer

Volume control circuit for speaker 4 ohm or 8 ohm located in the another room far away. by using only passive components. a simple circuit you can build at home at low cost it uses just a rotary switch and wire wound resistors. Add more resistors and a rotary switch with more contacts for finer control.

 Posted by admin at 3:56 PM

Mains Current Indicator with a LED

 Discrete-Circuits, LED-Circuits, Mains-Power  No Responses »
Nov 302004
 
Mains Current Indicator with a LED

This is a mains 230V AC load current indicator and is a LIVE CIRCUIT, so take care. The Resistors have to be a fusible ceramic wire wound. This circuit has been drawn from my memory and i have not tried it out again, just see if it is ok and then try. You should use the fuse of 1A a slow blow if you want but it is very important. You can design the shunt R3 and Fuse rating as required by your load. Note that this circuit is to be put in series with the load like an ammeter. Read More …

 Posted by admin at 2:47 AM

Mains Voltage Indicator with a LED

 Discrete-Circuits, LED-Circuits, Mains-Power  No Responses »
Nov 302004
 
Mains Voltage Indicator with a LED

This is a mains 230V AC voltage indicator and is a LIVE CIRCUIT, so take care. The Resistor has to be a fusible ceramic wire wound and the capacitor 630V AC or higher capacity. This circuit has been drawn from my memory and i have not tried it out again, just see if it is ok and then try. You should use the fuse of 100mA a slow blow if you want but it is very important. This circuit has to be enclosed in a plastic sealed enclosure to avoid contact.

 Posted by admin at 2:46 AM
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