555 timer icClock & Timer Circuit Diagrams

Single-IC Timer Schematic Circuit Diagram

Simplified Timer Design with 1CM7250 Timer Chip

Maxim’s 1CM7250 timer chip simplifies the process of designing a timer. This integrated circuit (IC) features eight programmable inputs, allowing the connection of devices like thumbwheel switches. The units are configured in BCD code, with the four lowest inputs (pins 1-4) representing units and the highest inputs (pins 5-8) indicating tens. Consequently, users can select any time between 00 and 99 units.

Understanding IC Timers

Integrated circuit timers (IC timers) are versatile semiconductor circuits used to generate or set timing for electronic circuits. These chips can execute single or multiple functions. The operation of an IC timer involves determining the on and off intervals in the output pulse using an external capacitor. The timer chips’ counting sequence defines their function. In the up direction function, the counter in an IC timer advances forward in the counting sequence. Conversely, the down counter function allows the counter to move backward. In the bi-direction function, the chip can set the counter for either forward or backward counting sequences.

Single-IC timer tubes Schematic diagram

Setting Time Units in the Circuit

The duration of each time unit is established by the components P1, R2, R3, and C1. For this specific application, time units of one second have been assumed, although other units can be easily chosen with minor adjustments.

Critical Parameters for Timing Network

Referring to the relevant datasheet, it’s crucial to note that the total resistance in the timing network must not exceed 22 MΩ, and the capacitor’s value should not be less than 10 pF. When opting for long time units, capacitors with minimal leakage currents must be utilized to ensure accuracy.

Operation and Output Control

Upon pressing switch S3, an internal bistable is reset, initiating the counter. The output of IC1 (pin 10) subsequently switches states, becoming low. Once the predetermined number of time units has passed, the output reverts to a high state.

Voltage Supply Range and Prototype Performance

The timer can operate within a voltage range of 2–9 V, despite the datasheet indicating a permissible limit of up to 16 V. In practical testing, the output remained consistently high, with supply voltages ranging from 9.5 V to 16 V.

Relay Control and Circuit Efficiency

The relay, connected to the output, is activated by a power transistor, T1. This Darlington transistor has the capability to handle currents up to 4 A. Remarkably, the circuit itself draws a mere 1 mA of current, showcasing its efficiency.

 

Single-IC timer tubes Schematic diagram

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