Although the light touch switch is known for its simple structure, low cost, and good switching characteristics, it is susceptible to contact jitter when the key is pressed. This mechanical jitter event leads to multiple on-off changes of the circuit, causing bit error. Unfortunately, jitter is an inevitable disadvantage of light touch switches that must be addressed in circuit design. Ultimately, the goal must be to eliminate bit error caused by jitter, noise, and other factors that may occur during key activation. Therefore, designers must prioritize reliable circuit operation to ensure optimal switch performance.
Jitter in touch switch keys can be eliminated through two methods, one of which involves a hardware circuit. The underlying principle is to utilize a trigger mechanism to lock the key's state, thereby mitigating any jitter. In this approach, the fixed contacts of the light touch switch are connected to the R and S terminals of an R-S trigger, while the moving contact is connected to the ground.
During normal operation, the Q end of the trigger is in the "1" state as the moving contact is connected to the s end. However, when the microswitch is pressed, the moving contact moves away from the s end and makes contact with the R end. After a few transitions, the R end gets stably connected, and the Q end of the trigger is set to "0" through the initial contact pulse formed when the light touch switch is connected to the R end. Let's rearrange the content to generate a highly similar version while ensuring it is based on the original text information.
Each subsequent bounce pulse will not alter the state of the trigger as the moving contact remains detached from the s end. To achieve stability and set the Q end of the trigger to "1", the light touch switch key is released, causing the moving contact to separate from the R end and collide with the s end. This collision is repeated multiple times until the s end is firmly connected. Traditionally, a specialized integrated circuit chip is employed to eliminate any jitter, effectively implementing the aforementioned principle.
One approach to mitigate jitter is to incorporate a software delay method and physically interact with the microprocessor in the switch. This entails introducing a delay in the key switch management program for transmitting data signal and initiating the start command. The key management program is responsible for determining the anti-jitter delay time, typically set at around 20ms. Following the delay, the key is read to ascertain if it remains closed, thereby confirming the key press. Moreover, this technique also prevents unintentional key activation when touching the switch.