ART
BEAUTY & WELLNESS
CRAFT
CULTURE & HISTORY
ENTERTAINMENT
ENVIRONMENT
FOOD & DRINKS
REVERSE ENGINEERING
SCIENCES
SPORTS
TECHNOLOGY
WEARABLES
Youblob (generated from this blueprint's notebook) · CC0
The Time-Delay Relay: Switching a Set Time Later
Many control jobs need a pause: start the motor, wait until it is up to speed, then load it; stop the burner, then run the fan a little longer to clear the heat; light the stairway, and switch it off a few minutes later. The time-delay relay does it. An on-delay closes its contact a set time after it is energised; an off-delay keeps its contact closed a set time after it is de-energised.
The earliest timed their delay with a dashpot — a piston pushing air or oil through a small adjustable hole — or with a bimetal warmed by a heater. Electronic relays charge a capacitor through a resistor and switch when it reaches a threshold.
This rung works out an RC delay and why capacitor tolerance and leakage limit it, draws on- and off-delay timing, and builds an on-delay relay with a 555 timer.
Beginner
About 3 hours
Instructions
1
1
The RC delay and its limits
The RC delay and its limits
Loading Jupyter Notebook...
2
2
Build a 555 on-delay relay
Build a 555 on-delay relay
On a breadboard wire a 555 as a monostable from a 9–12 V supply: pins 4 and 8 to the supply, pin 1 to 0 V, a resistor R from the supply to pins 6 and 7 joined, a capacitor C from pins 6 and 7 to 0 V, 10 nF from pin 5 to 0 V, and pin 2 (trigger) held high through 10 kΩ with a push button to 0 V.
Pin 3 goes high for 1.1 RC after the button is pressed. Drive an NPN transistor from pin 3 through 1 kΩ, with the relay coil between the supply and the collector and a diode across the coil, reversed, to catch the coil's kick. Wire an LED through the relay's contact.
Time the relay with a stopwatch for three values of R. Plot delay against R: a straight line whose slope is 1.1 C. Swap in a second capacitor of the same marked value and watch the delay change — its tolerance.
Materials for this step:
NE555 Timer IC1 piece
NPN Transistor1 piece
SPDT Relay1 piece
Diode1 piece
Capacitor Kit1 piece
Resistor Kit1 piece
Push Button1 piece
5mm LED1 piece
Breadboard1 piece
Jumper Wires1 piece
Time Delay Relay1 pieceTools needed:
DC Power Supply
Multimeter
Stopwatch3
3
The relay it times
The relay it times
A time-delay relay is a relay with a clock in front of it. The embedded blueprint shows the electromagnetic relay it drives.
4
4
A timer that times wrong
A timer that times wrong
Time-delay relay faults.
Flow
Loading...
5
5
Context and honest limits
Context and honest limits
Pneumatic dashpot timers, thermal timers and motor-driven timers served machine and process control for decades; the 555 timer IC, introduced in 1972, made cheap electronic delays universal, and programmable controllers now provide timers in software.
**Honest limits.** An RC delay drifts with temperature and with the capacitor's age. For accurate long delays use a crystal-timed or counting timer. A relay switching mains loads must be wired and enclosed by someone qualified; the bench build stays at low voltage.
Materials
11- 1 piecePlaceholder
- 1 piecePlaceholder
- 1 piecePlaceholder
- 1 piecePlaceholder
- 1 piecePlaceholder
- from$5.60
- from$0.51
- from$9.36
- from$1.59
- 1 piecePlaceholder
Tools Required
3- Placeholder
- Placeholder
- Placeholder
Related Blueprints
These blueprints share knowledge with this one — techniques, materials, or principles that connect them in the learning graph.
CC0 Public Domain
This blueprint is released under CC0. You are free to copy, modify, distribute, and use this work for any purpose, without asking permission.
Support the Maker by purchasing products through their Blueprint where they earn a Maker Commission set by Vendors, or create a new iteration of this Blueprint and include it as a connection in your own Blueprint to share revenue.