Mic-Level Controlled Relay-0.5 to 5 s Delay

The RDL ST-ACR1M provides relay switching controlled by a microphone-level audio signal. It senses both audio activity and silence, operates double-pole-double-throw contacts, and supplies an open-collector SLAVE output for an indicator or compatible LCR relay. Adjustable sensitivity and release-delay controls let the module respond to the required signal threshold and determine how long the relay remains active after audio falls below that threshold.

Ideal Use Cases

This model is intended for audio systems that require switching based on the presence or absence of a microphone-level signal. Its DPDT contacts provide two-pole, double-throw switching, while the SLAVE output can drive an indicator or a slave LCR relay. The adjustable release delay makes the ST-ACR1M appropriate when the relay must remain active for a defined interval after the sensed audio stops. It can accept a balanced or unbalanced source, allowing it to integrate with either connection arrangement.

Why Choose This Model

The ST-ACR1M combines audio sensing, silence sensing, relay switching, and a separate control output in a compact module. A SENS potentiometer adjusts the microphone-level input sensitivity, and an audio-threshold LED supports accurate setup. The SENS control information specifies a trigger range from -65 dBu to -20 dBu. A dedicated DELAY control adjusts the nominal relay release time from 0.5 to 5.0 seconds, so sensitivity and release behavior can be configured independently.

Installation and Integration

The audio input is a 10 kΩ balanced-bridging input and may be connected in either balanced or unbalanced form. Power requires a ground-referenced 24 Vdc supply at 50 mA; the stated requirement assumes a maximum 20 mA load at the SLAVE output. Recommended power supplies, which are not included, are the PS-24AS for the USA and PS-24AX for international use.

The open-collector control output is rated at 25 mA and is identified as suitable for driving indicators or a slave LCR relay. The module measures 0.7 inches high by 3 inches wide by 1.6 inches deep, equivalent to 1.7 by 7.6 by 3.9 cm. Its specified ambient operating range is 0°C to 55°C. These published dimensions, power requirements, and operating limits provide the essential information needed when planning placement and system power.

Performance Highlights

Relay activation response time is specified at 25 ms, with a 250 ms retrigger delay. Once audio drops below the selected threshold, the DELAY setting determines when the relay releases, with an adjustable nominal range of 0.5 to 5.0 seconds. The switching contacts are double-pole-double-throw, and the published maximum switching specification is 60 W, with listed ratings of 220 Vdc, 125 Vac, and 2 A.

The threshold LED gives direct visual feedback during sensitivity adjustment. Together with separate SENS and DELAY potentiometers, it allows the input threshold and release timing to be set for the connected audio source rather than relying on fixed operating values.

What Makes It Different

The ST-ACR1M is centered specifically on microphone-level signal control. It does more than detect audio: it also provides silence sensing, adjustable delayed release, DPDT switching contacts, and an open-collector SLAVE output within one module. The balanced-bridging input supports balanced or unbalanced wiring, while the threshold indicator assists with configuration. This combination provides both direct relay action and a separate low-current control path from the same sensed audio signal.

Final Assessment

The RDL ST-ACR1M is a focused choice for systems that need microphone-level audio or silence to control relay contacts. Its 25 ms activation response, adjustable 0.5-to-5.0-second nominal release delay, DPDT contacts, and 25 mA SLAVE output define its core capabilities. Before integration, match the connected load to the published switching limits and provide the required ground-referenced 24 Vdc power supply.