Clock & Timer Circuit DiagramsFeature Slider

2/4/6-hour Timer Schematic Circuit Diagram

Solid-State Relay Timer Circuit Overview

This circuit provides a straightforward solution to drive a solid-state relay, allowing users to select a time period of 2/4/6-hour. It plays a crucial role in the author’s project, enabling remote control of a heating system via telephone, specifically in a holiday home scenario. The primary objective of the circuit is to mitigate the risk of the heating system running excessively in case of issues, ensuring it doesn’t operate beyond a specified duration when there’s no one available to intervene or switch it to a frost protection setting.

2-4-6-hour Timer Schematic Circuit Diagram

A pulse of one second or longer on pin 6 of the microcontroller sets off the timer and the output is energized. Once the chosen time has elapsed, the microcontroller deactivates the output.

The duration is selected via the DIP switches connected to ports GP2 and GP3:

2,4,6-hour Timer Schematic

Selecting a Suitable Relay

When selecting a relay for this circuit, it’s crucial to consider the maximum current that the microcontroller output can source, which is limited to 25 mA. It is advisable to opt for a solid-state relay, and you can find various suitable options discussed in this issue.

Software Implementation and Availability

The software for this circuit has been developed using E-Blocks Flowcode, and the complete project files can be accessed at [1]. For individuals who do not have access to Flowcode, alternative versions of the project are provided, including files in C and assembler languages, along with a HEX file. The preprogrammed microcontroller required for the circuit, specifically the PIC12F675 in an 8-pin DIL package, is available for purchase from the Elektor online store under part number 110219-41 [1].

Internet Link


Understanding Your Pulse

Your pulse is a measure of your heart rate, indicating how many times your heart beats per minute. With each heartbeat, your heart contracts, pushing blood through the arteries in your body. This action creates a momentary increase in pressure within the arteries, reflecting the heart’s effort to maintain circulation.

Introduction to PIC12F675 Microcontroller

The PIC12F675 is an 8-bit CMOS microcontroller manufactured by MICROCHIP TECHNOLOGY. It operates on a high-performance RISC architecture, making it a preferred choice among hobbyists and engineers. Its popularity can be attributed to its affordability and compact size, making it versatile for various applications.

Product Feature

    • 128 bytes of EEPROM data memory
    • Programmable pull-up resistors
    • 4 oscillator selections including a 4 MHz RC oscillator with programmable calibration and Power-On Reset

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