Schematic, Amazon Relay Module: 1 Channel, Optocoupler Isolation Hi/Low Trigger

A ham radio friend (Dan, KA6RCZ) recently purchased an inexpensive single channel relay module (made by HiLetgo, in this instance) from Amazon, and he wanted to know if it would work in an application he had planned.  

Because of local high noise at his location, Dan uses a remote webSDR site (KFS) through his PC for the receive side of his communications, and he wanted some way to turn off the PC's audio (to an external speaker) whenever he was transmitting.

Unfortunately, the module came with no documentation, and so to verify if it would work in my friend's application, I decided to draw its schematic.

This schematic was created from tracing out the circuitry of the 12 V version of the module, but it is probably applicable to the other voltage versions of the same module (e.g. the 5V relay module), assuming that the only change between different modules is the voltage rating of the relay.

Note that when the jumper is in the 'H' position, the relay turns ON when the IN voltage is raised to about 1.5 V above ground (i.e. 1.5 V above the voltage at the DC- connector).  This threshold should be independent of the spec'd relay voltage, assuming that the only component that changes between different voltage-rated modules is the relay.  

So, for example, a 5V relay module should turn on when the IN voltage is above about 1.5 V (note: IN voltage level referenced to the DC- pin). 

When the jumper is in the 'L' position, the relay turns ON when the IN voltage is less than about 1.5 V below DCV (where 'DCV' is the DC voltage applied to the module between the DC+ and DC- inputs).  

So, for a 5V relay module with 5 VDC applied between the DC+ and DC- connectors, I'd expect the relay to turn ON when the IN voltage is less than about 3.5 V (note:  IN voltage level referenced to the DC- pin).

A Circuit for Dan's Application:

I drew the connection diagram, below, for Dan's webSDR application.  

Please note the following:

1. An Icom 7300 controls the relay module's on/off state using the radio's back-panel "SEND" jack.
2. The module's JUMPER should be in the 'L' (not 'H') position.
3. DC power to the module is assumed to be 13.8 VDC (i.e. the same voltage as the radio's power).
4. An optional series Capacitor and Resistor can be added between the module's IN and DC-  terminals to delay when the module turns off at the end of TX.  This delay is to prevent you from hearing the end of your transmission when you transition back to RX (there is typically a delay in the webSDR audio). The value of the capacitor sets the "release" delay (47 uF gives roughly 300 msec of delay), and the resistor limits the current into the SEND jack at the start of TX, when the capacitor discharges (the SEND jack is rated at 0.5A, max).

Standard Caveat:

As always, I might have made a mistake in my equations, assumptions, drawings, or interpretations.  If you see anything you believe to be in error or if anything is confusing, please feel free to contact me or comment below.

And so I should add -- this information is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.