Products

Circuit - Design Considerations

- Connection Configuration
- Membrane tail or cable

CONNECTION CONFIGURATION: By connection configuration, GGI International means array circuits or circuits with a common connection. GGI International recommends that you entrust the connection configuration to its professional team of engineers so that they can optimize the circuit and reduce its manufacturing costs to a minimum. During the design stage, GGI International engineering can adapt to most any predetermined configuration, whether it be an array with a common connection or a combination of both.

  • Circuit with a common connection: Each component of a particular circuit (Dome, LED, or non-tactile) must be connected to a minimum of 2 traces. Consequently, the simplest configuration for a circuit is where a trace is used to make contact with all the components and other independent traces are assigned individually to each component.

    Representation of a common connection diagram on 8 traces for 5 LEDs and 2 keys

    Pin# 1 2 3 4 5 6 7
    8 L3 L4 L5 L1 S1 S2 L2
    • Advantages:
      • Usually, a simple configuration for circuits having few components.
      • Possibility of having more than one common connection for each circuit.
      • Requires low voltage for elements placed in parallel.
      • If all LEDs do not have to be lit at the same time, the common connection can be assigned to several LEDs.
    • Disadvantages:
      • The trace acting as the common connection can carry a maximum current of 100 mA.
      • Considering that each LED requires a minimum of 20 mA to function adequately, if all LEDs must be lit at the same time, this means that each common connection can only support 5 LEDs.
      • The number of necessary traces can be very high (one trace for each component and one or more traces for the common connection).

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  • Array circuit: The array circuit, as its name indicates, is arranged as an X by Y array. This arrangement makes it possible to significantly reduce the number of traces. For example, let us suppose that we have a circuit comprising 20 domes. In a configuration with common connection, a minimum of 21 traces would be required to make this circuit. On the other hand, with an array circuit, only 9 traces would be required using a 4 x 5 array.

    Representation of an array on 9 traces for 20 keys

    Pin# 1 2 3 4 5
    6 S1 S5 S9 S13 S17
    7 S2 S6 S10 S14 S18
    8 S3 S7 S11 S15 S19
    9 S4 S8 S12 S16 S20
    • Advantages:
      • Considerable reduction of the number of required traces
      • Large variety of possible combinations
    • Disadvantages:
      • The layout of this type of circuit is often complex and usually requires the use of crossovers in order to create bridges between the various traces.

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  • Mixed circuit: Finally, according to the complexity of the circuit or simply by customer request, GGI International can offer you a combination of the two types of circuits mentioned above. The general tendency is that LEDs share a common connection and that the keys are arranged in an array. It is then possible to benefit from the best of both worlds.

    Illustration of a array circuit with 11 traces for 5 keys and 4 LEDs

    Pin# 1 10 9
    2 L1  
    3 L2
    4 L3
    5 L4
    6   SW1  
    7 SW2 SW4
    8 SW3 SW5
  • MEMBRANE TAIL OR CABLE: The membrane tail is not a separate cable but rather an integral extension of one or more circuit layers in the membrane interface assembly. The tail of the membrane switch keypad is a flexible extension which allows the electrical interconnection with the electronic components. It can include several traces (a minimum of two), whose width and spacing are determined by the application and the type of connector required for the application.
    • Important characteristics and notes:
      • To change the length of a tail does not mean to replace it by a new one. The tail is an integral part of the circuit therefore a new circuit is required.
      • It is possible, but costly to lengthen the tail by adding an extension cable.
      • A tail should never be folded nor curved with a radius smaller than 0.100" (2.5 mm).
      • If a pronounced curve is required, GGI International can provide stress-free thermoformed elements.
      • The exit position of the tail should not affect the position of the switches or the LEDs.
      • For more protection against electrostatic discharges and abrasion, tails can include a layer of laminated polyester to seal the conducting traces.
      • GGI International is able to produce tails with complex forms to meet your needs.
    • Basic information required by GGI International:
      1. Length of the tail
      2. Position of the tail exit
      3. The number of traces
      4. Distance between traces
      5. Position of trace #1
      6. Type of contact or connector
      7. If available, size of the opening in the housing or backer which the tail will fit through.

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