Jim Andrews, KH6HTV developed a circuit to control the PTT line for his repeater so when the receiver detected a valid signal it would turn on the transmitter. This is the same one used in the W0ATN repeater. The PTT line is connected to an open collector transistor which could turn on other things like a relay, another light or in this case, a visual and audio alarm. Refer to the schematic and PCB layout.
The alarm “beeping” level may be controlled by simply blocking off the hole on its miniature “Sonalert” type of audio indicator. The alarm is available from eBay and Amazon for a few dollars. A switch was included to “disarm it.” A low cost plastic enclosure would work fine too. The interface between the Green LED and the alarm is made with a small PC Board mounted inside the receiver. The 2N3904 Bi-polar NPN transistor will handle up to a couple of hundred mills at a nominal 12vdc. Refer to the docs and pictures for building one for your Hi Des HV-110/120 or 122 DVB-T receiver. A bare PCB is available free to SLATS club members. Thanks to Bob, KD0JIY for help with the PCBoard design developed using open source KiCaD.
12v at <50ma. RCA cable for signal to alarm
Inside view showing the Alarm. Come in a variety of colors (and prices!). P/N uxcell AD16-22SM 12v
Enclosure found at surplus house.
Schematic of the Alarm circuit
Valid Signal Board available from K0PFX
Valid Signal PC Board in a HV-120/122 receiver. PCB is located on top of the HDMI connector using double sided foam tape. 1/8th jack used here for PTT out.
Connection to the RED/GREEN LED made here for HV 120/122 receivers
Valid Signal PC Board in a HV-110 receiver. PCB is mounted using double sided foam tape. RCA jack for PTT out to alarm.
Connection to the RED/GREEN LED made here for HV 110 receiver.
For more information or questions, please contact Mel, KØPFX, using the Contact Us page. Happy building!