electronics question Parallel port Relay?
hi i have a question about this circuit
http://www.dehnes.com/pp_powerSwitch/switch.html
im a beginner and i have a few questions .
1. where do i connect the "ground" to the - sign ?
2.in the relay coil , do i simply connect two ends of a cable from something like a light , or small motor ?
Thank you!
Answers & Comments
Verified answer
(1) In electrical engineering, the current flow is possible only if circuit is complete. To make relay operative the negative terminal of battery is to be grounded, i.e. ground the –ve terminal.
(2) A relay has two terminals meant to carry a current through its coil. This is the current that makes relay operative, hence sometimes it is referred to as controlling current. Other than these two terminals, relay has contact points. These contact points may be N/O or N/C. N/O means the terminals are normally open and get closed when current flows through the coil., i.e. the circuit connected to the contact points becomes closed. Contrary to this is the case with N/C contacts. They are normally closed and get opened when coil carries current. How much load can be connected to these terminals depends upon the current making and breaking capacity of the contacts, which every manufacturer specifies. The capacity is different for ac and dc systems. Generally it is high for ac system.
As you r a beginner, I add some other information about this circuit.
(i) The circuit will be operative when output from the parallel port pin is HIGH.
(ii) If u change the switch position to ground the lower end of the coil, it will carry current continuously, and u will loose the comtrol.
1. Ground over here is the same as negative (B-).
2. Do not connect any light or motor to the relay coil. There is at least one switch or more including inside the relay. As the relay close or open,the contacts (switch) become ON or OFF. You need to feed power to one contact. Another contact connect to a light or motor. Using this relay circuit as an electronic switch to control light or motor.
the power supply (-) for the +5 or +12 volts power supply for the relay is connected to ground at pin 25 on the connector.
in addition to the relay coil terminals, the relay may have three contacts: a common, a normally open and a normally closed. you will be interested in the normally open and common contacts. when the relay is energized the normally open contact is connected to the common. this connection completes a circuit like lighting a LED or other function.