Loop Detect Board

Model: LDB-1

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Product Manual

Product Details

The LDB-1 provides a loop activated contact closure when used in series with telecom devices on analog phone lines. The LDB-1 will initiate a dry relay contact on any off-hook condition. Alternatively, add the optional PS-2 power supply to provide switched DC power.

The relay itself is phone line powered and does not need an external power supply. Because both TIP and RING currents flow through the relay, excellent line balance is maintained.


  • Provide relay closure on off-hook
  • Trigger a security camera
  • Trigger a tape recorder
  • Phone “In Use” indicator


  • FCC Part 68
  • FCC Part 15


  • Dimensions: 47.6mm x 30.5mm (1.875” x 1.2”)
  • Mounting: (2) #4 screws (not included) or foam tape (included)
  • Shipping Weight: 0.45 kg (1 lb)
  • Added Loop Resistance: 40 Ohms
  • Maximum Loop Current: 125 mA
  • Minimum Loop Current: 18 mA
  • Operating Temperature: -26° to 54°C (-15° to 130° F)
  • Maximum Supply Voltage Input: 35 VDC
  • Maximum 12V Supply Current: 500 mA with PS-2
  • Longitudinal Balance: 63 dB minimum
  • Maximum Contact Voltage: 200 VDC
  • Maximum Contact Current: 500 mA
  • Maximum Contact Power: 10 W Resistive*
  • Connections: 7 pin screw terminal block

* Note: If driving an inductive load a protection device must be placed across terminals 6 and 7.