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MR350 Assembley Instructions

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

This is a one shot, also known as a ‘monostable timer’. When the timer is triggered by it
will remain ON for a predetermined period set by a pre-set. The preset varies the time ON
from approx. 1 sec to 120 seconds. The ON time can be Reset to OFF by a second switch.

The timer is available fully assembled and tested MR350, or as a Self-assembly kit MR351

Basic operation:
The timer is started by a normally open contact connected across SW2 this could be a push
button switch, leaf switch, reed switch, etc. This activates the relay and starts the timer. The
relay will change state and remain in the new state for the timer period. There is also a
normally open Reset switch SW1 to reset the timer to OFF. The reset can be used at any time
during the ON period

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 pre-set fully anticlockwise and then a 1/4 turn clockwise.

Connect a 12 v supply to the + - terminals, take care to get the correct polarity, with this connected and the power switched on nothing should happen.

Connect a normally open switch to the SW2 (Start) terminals. press this switch and the LED should be ON and the relay will have energised. After a short period the LED should switch OFF, this indicates the timer has finished its cycle.

It will take a little trial and error to set the pre-set to give you your desired 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.

Connection to the Timer.
The following drawing shows how to connect your power supply, START switch or sensor & the RESET switch if you are using one.
To set the time period move the Preset (shown below) from left for minimum time &  right for a longer ON time.
                                                                                                                The time period can be from 1 second to 120
                                                                                                                seconds. To get an exact time is unfortunately
                                                                                                                a little trial and error.

                                                                                                                The Green LED on the circuit board will be
                                                                                                                Illuminated during the time period.

                                                                                                                The relay will be energised during the time
                                                                                                                period. You have 2 changeover contacts
                                                                                                                available. Both contacts are rated at 2 Amps.

An example of using one set of change-over
contacts on the timer. With the timer off but
power on the + - terminal of the timer, and
the lamps wired as shown, the RED lamp
will be ON. When the timer is started the
RED lamp will go out and the GREEN lamp
will come ON. The green lamp will stay on
for the duration of the ON time.

The other set of changeover contacts could
be used to drive a buzzer, or motor, or any
item you want on for the time period.