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Author Topic: Adding scanning to radio with up down buttons  (Read 1740 times)
KE1JR
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Posts: 17




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« on: October 03, 2012, 08:56:00 AM »

If there was a radio with push button up / down channel selection but no a way to scan stored memories, could a simple circuit be added to perform a scanning function to find active channels?

I was thinking an add on circuit could be 'piggie-backed' on either the up or down button switch. Once a second it would close the switch momentarily to move a channel then stop switching when it detects a signal, possible by monitoring the the speaker wire. To resume scanning the 'scan' button would need to be pressed again to restart the process.

Should be fairly easy to make something to trigger the switch so that the radio advances a channel but I'm not sure about making it stop when it finds an active frequency.

Any suggestions or experience? I'm looking at various switch projects to see if anything can be adapted.
Thanks
Dave



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W4OP
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Posts: 423


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« Reply #1 on: October 03, 2012, 09:22:07 AM »

Hi Dave,
You should be able to use an NE555 timer chip in astable mode and a transistor switch to toggle the UP or DOWN circuit (this assumes when  the upper or lower limit is reached, it rolls over). Then also monitor the squelch line to disable the astable when the squelch is opened for a preset dwell time. A second NE555 would be configured in timer mode to set the dwell time.

GL,

Dale W4OP
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W9GB
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Posts: 2623




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« Reply #2 on: October 03, 2012, 01:34:39 PM »

Quote from: KE1JR
If there was a radio with push button up / down channel selection but no a way to scan stored memories, could a simple circuit be added to perform a scanning function to find active channels?
You won't place this circuit in the microphone.
Such a circuit would need to be IN the radio, for access to other analog and/or digital signals, such as the squelch line, as mentioned by Dale, W4OP.

There were a large number of these adaptations in 1970s amateur literature (NE555 and discrete transistors) for crystal VHF/UHF radios to provide a scanning function.

PULL UP the schematic for the radio you desire this function .... That will be a starting point.
You need to UNDERSTAND how your current radio works, BEFORE modification -- otherwise it's an ill-advised hack.

w9gb
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