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Versatile Multi-Mode Timer

Versatile timer is based on an Atmel microcontroller and has seven different operating modes.

By Frank Crivelli & Peter Crowcroft

Everyone who becomes involved with electronics builds a timer at one stage or another. There are thousands of designs using a variety of circuits, some of which have been around for decades. Witness the 555 timer IC, for example. This is one of the longest surviving ICs, being introduced about 30 years ago.

In the past, most timers were quite specialised in that they only performed one function - eg, an egg timer, a delayed timer, a timeout timer, a flasher, or a photographic timer, etc. Those days are now well and truly over - microcontroller ICs now allow us to easily design multi-purpose timers that can perform a variety of tasks, all at very low cost.

And that's exactly what you get with this new "Multi-Mode Timer". It supports no less than seven different timing modes using two ICs and a handful of other parts.

The various timing modes and delay ranges are selected using on-board DIP switches. You simply select the time delay you want and that's it - no further adjustments are required.

An optocoupler is used for the trigger input and this allows for complete electrical isolation between the trigger source and the remainder of the timer circuitry. This is important when high voltages are to be used for triggering the timer. An on-board relay provides electrical isolation of the output as well.

Operating Voltage 12VDC (see text)
Trigger Voltage 6-81V DC (see text)
Trigger Current 5mA minimum; 80mA maximum (see text)
Trigger Pulse Width 20ms minimum
Relay Contact Rating* 10A @ 240V AC max.
Timing Modes 8 (see text)
Timing Ranges 1-255s, 10-2550s, 1-255 minutes, 10-2550 minutes

NB: although the relay contacts are rated at 240VAC, the relay should be limited to switching voltages up to about 40-50V DC or AC. DO NOT use the on-board relay to switch 240VAC (mains) voltages (see text).

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