Slide-show-timer
Description: The interval can be set between approximately 5 to 30 seconds. A relay controls the slide-change mechanism. Operational amplifier U1 functions as a type of Schmitt trigger. Resistors R1 and R2 bias the non-inverting input at pin 3 of U1 to half the supply voltage. Feedback resistor R3 adjusts the bias at pin 3 based on whether the output of U1 is high or low. Initially, when power is applied to the circuit, capacitor C2 is uncharged, causing the inverting input of the op-amp to be at a lower voltage than the non-inverting input. When the output of U1 is high, C2 starts charging through resistor R5 and diode D1.
It takes approximately one second for the voltage across C2 to equal that of the non-inverting input of U1. At this point, the output of U1 begins to swing negatively. Due to positive feedback through R3, the voltage at the non-inverting input decreases, resulting in a further negative output. The voltage at the non-inverting input is about half of the supply voltage, and C2 begins to discharge through a resistor bank. The timing is governed by resistor R6. The resulting pulses are directed to the base of Q1, which is configured as an emitter-follower buffer stage, activating relay K1. Transistor Q1 is essential as operational amplifiers typically have an output current capability in the range of 20 mA, insufficient to drive the relay.
The circuit operates with a relay that engages a slide-change mechanism at user-defined intervals, adjustable between 5 and 30 seconds. The core of the timing mechanism is the operational amplifier U1, which functions as a Schmitt trigger. The biasing of the non-inverting input is achieved through resistors R1 and R2, which set the threshold voltage for the trigger action to occur at half the supply voltage.
When power is initially applied, capacitor C2 is at 0 volts, causing the inverting input to be lower than the non-inverting input, which prompts U1's output to go high. This output causes C2 to charge through resistor R5 and diode D1, allowing a gradual increase in voltage across C2. After approximately one second, the voltage across C2 matches the voltage at the non-inverting input, prompting a transition in U1's output to a low state. This low output, amplified by the positive feedback from resistor R3, drives the non-inverting input voltage down, resulting in a further negative output swing.
As the voltage at the non-inverting input approaches half of the supply voltage, C2 begins to discharge through the resistor bank, controlled by R6, which sets the timing for the relay activation. The pulses generated from this discharge are fed to the base of transistor Q1, which is configured as an emitter follower. This configuration allows for a higher current output than the op-amp can provide, ensuring that relay K1 is adequately activated to perform the slide-change mechanism. The use of Q1 is crucial, as the output current from the op-amp is typically limited to around 20 mA, which is insufficient for the relay's activation requirements. Hence, Q1 serves as a buffer, amplifying the current to successfully engage the relay.You can set the interval from about 5-30 seconds. A relay operates the slide-change mechanism. Op amp Ul forms a sort of Schmitt trigger. Resistors Rl and R2 bias the noninverting input at pin 3 of Ul to half the supply voltage. Feedback resistor R3 increases or reduces the bias to pin 3, depending on whether the output of Ul is high or low. When power is first applied to the circuit, C2 has a zero charge and the inverting input of the op amp is at a lower voltage than its noninverting input.
When the output of Ul is high, C2 begins to charge through R5 and D 1. It takes about one second for the charge on C2 to reach the same voltage as that at the noninverting input of Ul. At that time, the output of Ul begins a negative swing. Because of the positive feedback through R3, the voltage at the noninverting input is reduced and the output becomes more negative.
The voltage at the noninverting input is about lf. of the supply voltage, and C2 begins to discharge through the resistor bank. The timing is controlled by R6. The resulting pulses are fed to the base of Ql, configured as an emitter-following bufferstage, which is used to activate relay Kl. Transistor Ql is necessary because op amps usually have an output current in the 20-mA range, which is too low to activate the relay.
It takes approximately one second for the voltage across C2 to equal that of the non-inverting input of U1. At this point, the output of U1 begins to swing negatively. Due to positive feedback through R3, the voltage at the non-inverting input decreases, resulting in a further negative output. The voltage at the non-inverting input is about half of the supply voltage, and C2 begins to discharge through a resistor bank. The timing is governed by resistor R6. The resulting pulses are directed to the base of Q1, which is configured as an emitter-follower buffer stage, activating relay K1. Transistor Q1 is essential as operational amplifiers typically have an output current capability in the range of 20 mA, insufficient to drive the relay.
The circuit operates with a relay that engages a slide-change mechanism at user-defined intervals, adjustable between 5 and 30 seconds. The core of the timing mechanism is the operational amplifier U1, which functions as a Schmitt trigger. The biasing of the non-inverting input is achieved through resistors R1 and R2, which set the threshold voltage for the trigger action to occur at half the supply voltage.
When power is initially applied, capacitor C2 is at 0 volts, causing the inverting input to be lower than the non-inverting input, which prompts U1's output to go high. This output causes C2 to charge through resistor R5 and diode D1, allowing a gradual increase in voltage across C2. After approximately one second, the voltage across C2 matches the voltage at the non-inverting input, prompting a transition in U1's output to a low state. This low output, amplified by the positive feedback from resistor R3, drives the non-inverting input voltage down, resulting in a further negative output swing.
As the voltage at the non-inverting input approaches half of the supply voltage, C2 begins to discharge through the resistor bank, controlled by R6, which sets the timing for the relay activation. The pulses generated from this discharge are fed to the base of transistor Q1, which is configured as an emitter follower. This configuration allows for a higher current output than the op-amp can provide, ensuring that relay K1 is adequately activated to perform the slide-change mechanism. The use of Q1 is crucial, as the output current from the op-amp is typically limited to around 20 mA, which is insufficient for the relay's activation requirements. Hence, Q1 serves as a buffer, amplifying the current to successfully engage the relay.You can set the interval from about 5-30 seconds. A relay operates the slide-change mechanism. Op amp Ul forms a sort of Schmitt trigger. Resistors Rl and R2 bias the noninverting input at pin 3 of Ul to half the supply voltage. Feedback resistor R3 increases or reduces the bias to pin 3, depending on whether the output of Ul is high or low. When power is first applied to the circuit, C2 has a zero charge and the inverting input of the op amp is at a lower voltage than its noninverting input.
When the output of Ul is high, C2 begins to charge through R5 and D 1. It takes about one second for the charge on C2 to reach the same voltage as that at the noninverting input of Ul. At that time, the output of Ul begins a negative swing. Because of the positive feedback through R3, the voltage at the noninverting input is reduced and the output becomes more negative.
The voltage at the noninverting input is about lf. of the supply voltage, and C2 begins to discharge through the resistor bank. The timing is controlled by R6. The resulting pulses are fed to the base of Ql, configured as an emitter-following bufferstage, which is used to activate relay Kl. Transistor Ql is necessary because op amps usually have an output current in the 20-mA range, which is too low to activate the relay.
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