Smart Foot Switch

Description: Tasks such as jewel cutting and polishing require workers to repeatedly turn on and off two electrical appliances in succession for different services on the same workpiece. This process can be cumbersome, as it demands full concentration on the delicate handling of precious jewels. Manual switching is impractical in such scenarios, and using ordinary foot-operated switches can be tedious due to the difficulty in sensing and controlling the switch position. Standard pushbutton switches only maintain a momentary contact, which does not suffice for this application. A bistable multivibrator with two independent trigger inputs is needed to address this issue. A foot switch design based on a dual negative-edge triggered master-slave JK flip-flop IC 74LS76 (IC1) is proposed. Inputs J1 and J2 are connected to 5V through 10k resistors (R2 and R5), while K1 and K2 inputs are grounded. The preset pins (2 and 7) are shorted and connected to 5V via a 10k resistor (R7). A push-to-on switch (S3) connected to the preset inputs is also grounded. The clock and clear inputs of the two flip-flops are cross-connected; CLK1 (pin 1) connects to CLR2 (pin 8), and CLR1 (pin 3) connects to CLK2 (pin 6). The clock input pins (1 and 6) are pulled high through 4.7k resistors (R1 and R4). Push-to-on switches (S1 and S2) connect the clock to ground for the flip-flops, with S1 activating device 1 and S2 activating device 2. Switch S3 activates both devices simultaneously. The status of the devices is indicated by LED1 and LED2, which glow to show that device 1 and device 2 are on, respectively. The LEDs connect from +5V to Q1 (pin 14) and Q2 (pin 10) of IC1 through resistors R3 and R6. Initially, when power is applied, Q1 and Q2 outputs of the JK flip-flops are low (logic 0). Pressing switch S1 for the first time transfers a high level (logic 1) from J1 to Q1 output on the trailing edge of clock (CLK1). This high level activates relay RL1 through pin 16 of ULN2003 (IC2), turning on device 1 via its normally-open contacts. The clock CLK1 of flip-flop IC1(A) is also connected to clear input CLR2 of flip-flop IC1(B), allowing for asynchronous clearing. The circuit is immune to switch bounce, as the same J1 state is transferred to Q1 output on subsequent trailing edges. Simultaneously, device 2 is turned off. When switch S2 is pressed, flip-flop IC1(A) is cleared via CLR1, and the high state at J2 input of flip-flop IC1(B) is transferred to Q2 output on the trailing edge of clock (CLK2). This high level activates relay RL2 through pin 15 of IC2, turning on device 2 via its normally-open contacts, while device 1 is turned off. To turn on both devices simultaneously, switch S3 is pressed momentarily, providing ground to the preset inputs PRE1 and PRE2 of flip-flops IC1(A) and IC1(B), making their Q1 and Q2 outputs high, which energizes both relays to activate both devices. The LEDs glow to indicate that both devices are on. It is recommended to place all three switches (S1 through S3) within easy reach for foot operation, and the LEDs should be mounted conveniently to indicate whether the devices are powered on.

This circuit effectively simplifies the operation of activating multiple devices in precision tasks, enhancing efficiency and safety for users engaged in delicate work. The use of JK flip-flops ensures stable operation with minimal interference from switch bounce, while the arrangement of relays allows for safe control of high-power devices. The design can be further enhanced by integrating additional features, such as a debounce circuit for the switches or an indicator for the power status of the entire system. The layout of components should be optimized for ease of use, ensuring that all switches and indicators are accessible and visible to the operator during the operation.Such jobs as jewel cutting and polishing require the workers to switch on/off two electrical appliances one after another repeatedly for two different services on the same workpiece. This is cumbersome as they need to fully concentrate on delicate handwork on precious jewels. Switching in such situations cannot be done by hand, and doing it by foo t using ordinary switches is too tedious. This is mainly because of the difficulty in sensing and controlling the switch position by foot. Ordinary pushbutton switches make or break a contact momentarily, and they can not hold the keypress status. You need a bistable multivibrator with two independent trigger inputs to solve this problem. Here`s a smart foot switch based on dual negative-edge triggered master slave JK flip-flop IC 74LS76 (IC1).

J1 and J2 inputs are conneted to 5V through resistors R2 and R5 (each 10k), respectively. K1 and K2 inputs are grounded. Preset pins 2 and 7 are shorted and connected to 5V via resistor R7 (10k). Push-to-on switch S3 connected to the preset inputs is also grounded. Clock and clear inputs of the two flip-flops are cross-connected, i. e. CLK1 (pin 1) is conneted to CLR2 (pin 8) and CLR1 (pin 3) is connected to CLK2 (pin 6). Clock input pins 1 and 6 are pulled up high through resistors R1 and R4 (each 4. 7k), respectively. Push-to-on switches S1 and S2 are connected between clock and ground of the flip-flops. Switch S1 activates device 1, while switch S2 activates device 2. Switch S3 activates both device 1 and device 2 simultaneously. Device status is indicated by LED1 and LED2. Glowing of LED1 and LED2 indicates that device 1 and device 2, respectively, are in on condition. The LEDs are connected from +5V to Q1 (pin 14) and Q2 (pin 10) of IC1 through resistors R3 and R6, respectively. Initially when the power supply is switched on, Q1 and Q2 outputs of the JK flip-flops are at low level (logic 0).

When switch S1 is pressed for the first time, the high level (logic 1) present at J1 input is transferred to Q1 output on the trailing edge of clock (CLK1). The high level (logic 1) at Q1 activates relay RL1 through pin 16 of IC ULN2003 (IC2), turning on device 1 via its normally-opened (N/O) contacts.

Clock CLK1 of flip-flop IC1(A) is also connected to clear input CLR2 of flip-flop IC1(B) so as to clear it asynchronously. Switch debounces don`t affect the circuit as the same J1 state is being transferred to Q1 output on succeeding trailing edges.

At the same time, device 2 is switched off. When switch S2 is pressed, flip-flop IC1(A) gets cleared via CLR1 and the high state of J2 input of flip-flop IC1(B) is transferred to its Q2 output on the trailing edge of clock (CLK2). This high level (logic1) activates relay RL2 through pin 15 of IC2, turning on device 2 via its N/O contacts.

At the same time, device 1 is switched off. Now if you want to turn on both the devices simultaniously, press switch S3 momentarily. Switch S3 provides ground to preset inputs PRE1 and PRE2 of flip-flops IC1(A) and IC1(B), making their Q1 and Q2 outputs high, which energises both the relays turning on the two devices. LEDs glow to indicate that both the devices are on. ` Place all the three switches (S1 through S3) where you can easily press them by foot when required.

The LEDs can also be mounted at a convenient location to know whether the devices are turned on.