In sports shooting competitions I attend, there is one requirement to shoot five shots onto a paper target either first 20 seconds (one "mode of competition"), and then another five shots within 10 seconds. To get used to the rhythm here, I am building a device that issues five beeps with the correct timing to be plugged into my electronic headset's line-level input (it's a Peltor SporTac active hearing protector).

Circuit description

The device has one power switch, three push-buttons labled "Start", "Mode", and "Prog", two LEDs colored red and green, and a connector to the headset's input plug. It is powered by a 9V "block" type battery. When turning on the device for the first time after manufacturing, it may start a counting sequence immediately, on its own. In this case, please press the "Mode" button once after the counting sequence has finished to have the device initialize its internal settings.

After turning the device on using the power switch, the red LED lights up while the green LED blinks a number of times, signalling the current mode of operation:

The interval mode can be changed by pressing the "Mode" button. After changing the timing mode, the LED signals the current setting as described above. Interval settings are saved even when the power is turned off, the device will start up with the same timing setting at the next power-on.

When the "Start" button is pressed, the shooting sequence is signalled:

Once the sequence has run, the next sequence can be started with the "Start" button, or another timing mode can be selected with the "Mode" button. A started sequence cannot be interrupted, but must run until the timer has expired and the signals described above have been given by the device. Power can be turned off at any time.

The "Prog" button is currently unused.


The case used is a "Bopla BOS 502", available e.g. from Conrad, order number 522473.

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The finished device in its case Photo of the inner workings Backside of the PCB