I used ohm resistor ohm resistor 12V AC source alternating current Breadboard SCR control with Arduino circuit: Example circuit schematic diagram is shown below. All grounded terminals are connected together. In the circuit there are two optocouplers, I used optocoupler 1 to detect the zero crossing of the AC voltage signal and optocoupler 2 for firing the SCR. The optocouplers are used to isolate the Arduino control circuit from the power circuit. Diodes D1 and D2 are with the same type 1N , D1 is used to protect optocoupler 1 from reverse voltage and D2 to feed the SCR gate with positive current.

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They are also called Thyristors. The figure on the left shows the standard electronic symbol of an SCR. It shows the three lead pin outs of the part, the upper one being the anode, the lower one the cathode, and the central extension the gate.

The symbol quite resembles an ordinary rectifier diode symbol having an extra lead from the cathode side. As you can see in the actual picture of an SCR on the right, it looks like a transistor.

Externally they may look exactly like transistors, but are entirely different as far as technical specifications are concerned. Both act as switching devices, although SCRs comfortably handle high voltage AC, whereas transistors normally are dedicated for low voltage DC applications.

The lead orientation specifies the first lead from the right to be the gate, the extreme left is the cathode, and the center pin is the anode. The gate and the anode leads always work with respect to the ground; the cathode lead is specified to be connected with the ground and serves as the common release terminal for the gate as well as the anode.

How SCRs Function Unlike transistors, which may show an exponentially varying output current pattern, equivalent to the applied input switching current, SCRs have specific triggering levels below which they may not conduct properly. However, once the trigger level crosses the optimal value, an SCR may swing into full conduction.

The following few simple SCR circuits are based on the above properties of the device. The circuit incorporates two transistors and one SCR as the main active components, touching the capacitor input immediately switches the Darlington transistor pair, which in turn triggers the SCR, sounding the bell. Since the load bell is being operated in the DC mode, latches on to ring continuously even after the input touch trigger is removed.

The unit may be used in door handles in restricted areas, such that the alarm gets triggered every time the handle is touched by an intruder in an attempt to open the door. Parts List.


Electronic ComponentTO-220 New original TYN1225



TYN1225 Datasheet, PDF, Circuit Diagram, Application Notes


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