features include Sense input which enables the IC, Save Memor for Valet Parking, Convenience Delay to maintain Unlock condition for short term interruptions of the Sense input and Save Status and Lock Status outputs which can be used for direct drive of LED indicators.
following simple example the use of LS 7220 as Electronic Combination Lock
Electronic Combination Lock
- C1 1uF/25Vr
- C2 220uF/25V
- R1 2.2K
- Q1 2N3904 NPN Transistor 2N2222
- D1 1N4148 Rectifier Diode
- K1 12V SPDT Relay, Any appropriate relay with 12V coil
- U1 LS7220 Digital Lock IC
- S1-S12 PST Momentary Pushbutton
- HD1 12 Position Header
To set the combination connect the appropriate switches to pin 3,4,5 and 6 of the IC through the header.As an example if S1 is connected to pin 3, S2 to pin 4 , S3 to pin 5, S4 to pin 6 of the IC ,the combination will be 1234.This way we can create any 4 digit combinations.Then connect the rest of the switches to pin 2 of IC.This will cause the IC to reset if any invalid key is pressed , and entire key code has to be re entered.
When the correct key combination is pressed the out put ( relay) will be activated for a preset time determined by the capacitor C1.Here it is set to be 6S.Increase C1 to increase on time.
For the key pad, arrange switches in a 3X4 matrix on a PCB.Write the digits on the keys using a marker.Instead of using numbers I wrote some symbols!.The bad guys will be more confused by this.