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    Deployment Timer

    This page describes our deployment timer. Its purpose is to  provide a delay after launch to release the parachute at apogee. The design consists of two parts: The NE556 which represents the actual timer and the NE555 which provides the pwm-signal to drive a standard servo actuator.

    Deployment Timer v1.2 assembled

    Schematic of the Deployment Timer

    Download the .sch file created with EAGLE.

    The timer has two stages. The first stage is triggered by the launch detect switch. It waits a defined time before triggering the second stage. The second stage provides a pulse with a duration of approx. one second. This causes the servo actuator to go to its "open" position for about a second.

    Notes:

  • Con1 is connected to a 6V battery. Currently we use four Duracell 1.5 Volt cells of the type "AAAA".

  • Con2 is connected to a standard servo actuator.

  • The delay time can be adjusted via R6. The value of 47k allows a delay of up to 5 seconds.

  • S3 is the launch detect switch. It is default OPEN. Once on the launch pad it will be held in the closed position by a magnet mounted at the launcher. After launch S3 opens again. When using a G-Switch remove R3 completely, remove S3 from V_Bat and connect it to ground.

  • In order to avoid EMC problems design a centre point for ground and Vbat. Supply the timer with an individual branch, use another branch for the single 555 and a third branch for T2. Use a blocking capacitor for each branch in case of persistent interference.

  • Place C2 close to T2 because of current peaks caused by the servo.

  • Follow the switch on sequence: Close S1 first, wait until the red Led lights up, then close S2.