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MR355 Assembley Instructions

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These Instructions show you how to assemble the timer & use it.

This is a Pulse timer, also known as a ‘bistable timer’. When the timer is triggered by applying power
to +- 12v terminals the timer will switch ON & OFF (pulse). The ON time is set by VR2, the OFF time
is set by VR1. This pulsing will continue until power is removed from +- 12v terminals.

Basic operation:
The timer is started by applying power to the +- terminals as shown in the drawing
below. The pulsing ON/OFF will continue until the power is removed.
Adjustment of the pulse is as follows. To increase the OFF time turn
the Variable Resistor VR1 to the right (clockwise), to increase the
ON time turn the variable resistor VR2 to the left (anticlockwise).
The output relay will be energised during the ON period (pulse).
The relay has two sets of changeover contacts, this means that
in the OFF (pause) state there is a circuit between the
COM and NC terminals, and in the ON (pulse) state
there is a circuit between the COM and NO terminals.
The Green LED behind the Variables will indicate when
the timer is in the PULSE state and will be Off during
the PAUSE state, use this indication to set the timer

You will need
Soldering Iron (no more than 30w)
Side cutters (miniature)
Ensure that each solder joint looks like a pyramid, and not like a round blob ( blobs usually mean a bad solder joint.

Now you must insert the Integrated Circuit IC1 into the 8 pin socket. You will need to bend the pins inward very slightly so that they line up with the IC socket. Please take care here.
Turn the preset VR1 to 3/4 to the right and VR2 1/4 to the left
Connect a 12 v supply to the + - terminals, take care to get the correct polarity, with this connected and the power switched on the timer will start to pulse, now adjust the 2 VR's to give you the desired ON/OFF time.

Once you have determined that the timer is working you can now connect it to the switches you want and the relay to control the circuit you require.

The following is an example of the timer being used, for further details see other projects on thehobbyshed.co.uk
A Simple Red /Green Flashing LED. If the Pause and Pulse are set the same then the Green will be ON for the Same Period as the Red.