Controlling A Relay With A Digital Logic Level Circuit

Description 

The schematic below illustrates 4 methods of controlling a relay with a digital logic signal. Figure (A) can probably be used in most cases where the relay coil requires 100 mA or less and the input current is 2 milliamps or more. The resistor value (R) is determined from the input voltage and the available current. For example, a 5 volt input signal supplying 2 milliamps would require (5-.7)/.002 = 2150 ohms, or a 2.2K standard value. If the transistor has a minimum current gain of 50, there will be 100 mA of current available for the relay coil. The following table shows various resistor values that can be used to obtain various relay coil currents assuming a transistor current gain of 50 such as the 2N3053. 74XX refers to standard TTL logic, 74LSXX refers to low power TTL logic, 74HC is high speed CMOS and CD40XX is the older CMOS devices. The currents given are approximate values and may not be correct for all devices but should be close. 

Input Voltage - Input Current - Relay coil current - Standard Resistor

• 4 - 74LSXX .0004 - 20 milliamps - 8.2K
• 4 - 74XX .0008 - 40 milliamps - 4.3K
• 4 - 74SXX .001 - 50 milliamps - 3.3K
• 5 - 74HCXX .004 - 200 milliamps - 1K
• 6 - 74HCXX .004 - 200 milliamps - 1.3K
• 5 - CD40XX .0003 - 15 milliamps - 13K
• 12 - CD40XX .0006 - 30 milliamps - 18K

Figure B can be used when the input voltage is the same as the relay coil voltage. The voltage on the emitter of the transistor will be about 0.7 volts less than the input, so a 12 volt relay would operate on 11.3 which should be close enough. No resistor is needed since the emitter follower configuration presents a high impedance at the input. The input current will be the relay coil current divided by the transistor gain. For example a 120 ohm relay coil will draw 100 mA at 12 volts and if the transistor gain is 50, the input current will be about 2 milliamps.

Figure C can be used to provide additional gain when the input current is very small. You can also use a Darlington transistor in place of the two transistors which is a better approach, but this idea works just as well when you dont have a Darlington transistor handy. The overall gain will be the product of the individual gains of the two transistors or about 2500 for two transistor with a gain of 50 each. This will enable supplying over 250 mA to the relay with only 100 microamps of input current. The R value will depend on the input voltage and current and gain of the first transistor. For example, using a 5 volt input and 100 microamp current and transistor gain of 50, the R value will be 5 minus two diode drops (5 - 1.4) divided by the input current times 50, or about (5 - 1.4) / (.0001 * 50) = about 750 ohms. So this setup can be used when controlling heavy duty relays with low power CMOS logic signals.

Figure D can be used to reverse the relay action so that it engages when the input is low and disengages when the input is high. The R value is determined the same as in Figure A. The R1 value should be high enough to ensure saturation of the first stage and low enough to saturate the second stage. For example, if a 12 volt relay coil requires 100 mA and the driving transistor gain is 50, then the base current will be 100/50= 2 mA and the R1 value must be less than 6000 ohms so that 2 mA does not drop more than the supply voltage of 12. If the first transistor gain is 50 and the input current is 100 microamps, the collector current will be 5 mA and the R1 value must be greater than 2400 ohms so that 5 mA drops the entire supply voltage of 12. So we need to select something between these two limits of 2.4K to 6K, something around 4.3K would be near the midrange.

Circuit Diagram

Source http://www.bowdenshobbycircuits.info/r_ctrl.htm

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Direction Sensor CMPS03

CMPS03 Compass Module Overview

Compass is a tool for navigation for a direction, a direction in this article referred to is the magnetic module CMPS03 Compas. Magnetic Compass Module CMPS03 often used in making robots in the contest.

Magnetic Compass Module Functions in the contest  CMPS03 usually to provide a reference where the robots are in position and lead anywhere, then the position and direction provided by the Magnetic Compass Module reference sebgai CMPS03 the next robot motion. Magnetic Compass Module uses I2C data communication lines to mirokontroler. With adalanya I2C data communication lines from this CMPS03 this module can be connected directly to a microcontroller that suport with I2C data communication channels such as AVR ATMega. Magnetic Compass Module CMPS03 require 5 V voltage with 15mA current.

CMPS03 Circuit Diagram

Because the module using I2C Magnetic Compass CMPS03 we can use 5 lines are:
VCC + 5 V on pin 1
SCL with Pull Up resistor 10 K
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Calibrate the PIN associated with micro switch 6
Ground on PIN9

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Telephone Call Recorder

Today phone has change into an essential component of our lives. It is essentially the most extensively used communique tool on the earth. Owing to its big reputation & in style use, there arises a necessity for name reporting gadgets, which find application in name cent-res, inventory broking corporations, police, offices, homes, and so on. Here they are describing a name recorder that makes use of just a few phases. But with the intention to remember its working, must first have the basic knowledge of standard phone wiring as well as a stereo plug.

In India, land-line rings essentially use RJ11 wiring, which has wireless-tip & ring. While tip is the certain wire, ring is the terrible. & together they full the cellphone circuit. In a phone line, voltage between tip & ring is around 48V DC when handset is on the cradle(idle line). In order to ring the telephone for an incoming name, a 20Hz AC current of round 90V is superimposed over the DC voltage already present in the idle line. The poor wire from the phone line goes to IN1, whereas the positive wire goes to IN2. Further, the poor wire from OUT1 & the certain wire from OUT2 are linked to the phone. All the resistors used are zero.25W carbon movie resistors & the entire capacitors used are rated for 250V .

The poor terminal of To AUX IN is linked to pin one of the crucial stereo jack while the certain terminal is hooked up to pins two and three of the stereo jack. This stereo jack, in turn, is related to the AUX IN of any documenting device, any suchs pc, audio cas-setts participant, CD participant, DVD player, and so on. Here they will be connecting it to a pc. When a call comes in, around 90V AC current at 20Hz is superimposed over the DC voltage already present within the idle line.

This current is transformed in to DC through the diodes & fed to resistor R1, which cut backs its magnitude & feeds it to LED1. The present is additional scale backd in magnitude by using the resistor R2 & fed to the suitable & left channels of the stereo jack, that are connected to the AUX IN port of a computer. Audio fileing application,can be used to file the decision. When a call is available in, needs to launch the audio documenting software and start documenting.

For phone documenting, basically connect the stereo jack to the AUX IN port of the PC. Install the Audacity audio recorder . Run the executable Audacity file. By & huge window, you'll discover a drop-down box within the top right corner. From this box, make a selection the AUX choice. Now you are ready to report any name. As soon as a name is readily available in, press the record button current within the Audacity primary window & then choose up the telephone receiver & answer the name. Press the stop button one time the decision ends. Now go to the file menu & choose the Export as WAVE choice & save the file in a desired location.

You may exchange the price of resistor R2 if you require to vary the output volume. You can use a variable resistor in collection with R2 to range the amount of the output. The recorded audio clip may additionally be edited the usage of different choices in the Audacity application. You can gather the circuit on a general-purpose PCB & enclose it in a small cupboard. Use an RJ11 connector & stereo jack for connecting the phone set & laptop (for call reporting). Phone twines can be utilized to connect to the telephone line & the circuit. Use of a shielded cable is beneficial to reduce disturbances in the fileing. These will also be scale backd by way of growing the price of R2 to about 15 kilo-ohms.

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Battery charger using LM350

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Notes

Use a 20 to 30 V / 3A DC power supply for powering the circuit.
This circuit is not possible for charging GEL type batteries as it draw large amounts of current.

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Green USB switch

According to the Energy Saving  Trust, if you add up all the current drawn in standby mode by items such as stereos, TVs, VCRs and DVDs over a year in the UK alone, it amounts to 3.1 million tonnes of CO2 released into the atmosphere.This is without factoring in the current drawn by all the PCs,laptops and their associated peripherals left in standby mode. 

Circuit diagram :

Green USB switch Circuit Diagram

It  is  not  necessary  to  spend  a  great deal of money or time to  make a difference on a personal  level. The circuit described here  is designed for use by laptop or  notebook computers. It will automatically switch off all mains  powered peripheral equipment  including monitor, printer, scanner, TV tuner and USB hub etc  when it detects that the notebook  is switched off. The circuit is quite  straightforward; in addition to an  optocoupler it requires a 12 V  double-pole  relay  with  mains  rated contacts and a small power  supply  for  the  optocoupler.  When the laptop is switched on  5 V appears at the USB socket,  activating the relay and switching  through  the  mains  supply  on K3 and K4. The notebook’s  USB socket is still available to be  used as normal but it’s worth remembering that the optocoupler  takes a few milliamps from the  USB supply and this may cause a  problem if a high-current device  is plugged into the USB socket.  In the case where the laptop has  more than enough USB sockets it may be worthwhile us-ing one of them solely for this  circuit, the extension USB connector K2 would then not be  required. 

The circuit is mounted into a  mains plug enclosure which  provides a socket where the  mains extension strip will be  plugged into. With any luck  there will be sufficient space  to fit the entire circuit into the  mains extension strip enclosure and save the need for a  separate enclosure. The slow-blow 6.3-A fuse (F1) protects  the equipment plugged into  the strip. 

In  addition  to  the  optocoupler  and relay the circuit also has a  ‘freewheel’ diode D1 and a relay  driver formed by T1 and its base  bias voltage divider network R2/ R4. The two ‘snubber’ networks  C1/R3 and C2/R5 reduce the  possibility of arcing which can  occur  when  the  relay  contacts  open (especially with inductive  loads). Capacitors C1 and C2  must be class X2 types which  can handle mains voltage plus any  spikes.  The  power  supply  consists of a small mains trans-former  (12 V,  50 mA),  bridge  rectifier and smoothing capacitor C3. 

The laptop’s mains adaptor itself  can also be switched by this circuit when the laptop is fitted with  its rechargeable battery which  allows the computer to boot up  without a mains supply. The en-tire USB switch circuit draws cur-rent even when it is off but this value  is  tiny  compared  to  the  combined standby current of all  the peripherals. 

Note that parts of this circuit are  connected to the (potentially lethal) mains supply voltage; it is  essential to provide protection  to ensure that nothing can accidentally make contact with these  parts of the circuit. It is also important to observe correct separation between parts of the circuit carrying low voltage and  those carrying the high volt-age. Please observe the electrical Electrical Safety guide-lines which are reprinted in  Elektor  Electronics  several  times a year. 

The  circuit  is  less  suitable  for use with desktop PCs be-cause  the  majority  of  these  machines supply 5 V over the  USB socket even though they  have been shut down via soft-ware. The only way to turn off  in this case is to reach around  the back of the machine and  switch off at the main switch. 

http://streampowers.blogspot.com/2012/06/green-usb-switch.html

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