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Discussion Starter · #1 · (Edited)
I'll start ;) Couple minutes with a dremel cutoff wheel to make an opening for the DTMF decoder LCD display and drilled some holes for the wiring, needs some more filing on those holes to get rid of the burrs...



A little hot glue to hold the decoder/LCD in place, small power bank to power it, and one of our HTs to act as the receiver.



Tones were sent from a different radio of course, this just displays them when plugged into the audio jack. Might add some weatherproofing to protect the display and to plug the gaps around the holes for the cables, and since this one will likely end up in our primary BOV need to find a small case/container to keep everything together in a glovebox/console kit.

So what's it good for? Maybe not too much - but how we might use it is to leave a message for a party that doesn't respond when called. Plug it in to your mobile radio when leaving your vehicle and someone calling you can leave a message on the display you'll see when you return. Or while working in a loud environment. Going to build at least two more of these and give them to a couple survivalist friends in our MAG, we have a HF comm (and bugout) plans with them and this would be handy to leave a message if someone is going to be away from their radio, or for sending encoded messages. Will have to work out the details of that latter part with them first. Anyway we likely won't have enough personnel to do a 24x7 radio watch so this is just a method to cut down on missed messages.

Parts used:

Altoids mints tin.

DTMF decoder (x4) w/32 character LCD.

2.5mm to 3.5mm audio cable (Kenwood/Baofeng headphone jack is 2.5mm, decoder uses a 3.5mm connector).
www.amazon.com/2-5mm-replacement-Headphone-QuietComfort-QC35II/dp/B0BRK9QM11

5V power adapter, USB to 5.5x2.1mm male adapter.
www.amazon.com/SinLoon-5-5x2-1mm-Connector-Electronics-Charging/dp/B08FY476MY

USB A to USB A male cable.
www.amazon.com/Ruaeoda-Double-Transfer-Compatible-Monitor/dp/B0B3TNSXQQ

Revisiting another radio related Altoids tin project I started on a couple years that needs some cleanup and will post that up in this thread once its finished, but what radio related DIY hacks/gadget projects do you have or are working on?
 

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I have used a Sucrets tin for electronics placing a wood block inside when drilling to avoid drill punch through worked out pretty well. My brother had a little chassis nibbler that worked well for rectangular holes, just mark the outline drill a hole and start nibbling.
 

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Discussion Starter · #7 · (Edited)
DTMF relay controller with 4 relays.




Spare relay board I had in the radio junk drawer/box, bought two when I was improving on the burglar alarm in the pole barn a few years ago. Only using two relays on that one, one to turn power on or off on a Dakota Alert mounted inside the barn and another for an outside entry light. The connection points for the relays are quite small, 14 gauge is about the largest wire that will fit, and the physical connection is not very strong so for this spare one I added a wiring panel on the underside of the Altoids box so it'll be easier to wire devices to each relay. The four connectors on the left in the second pic are connected to the 'normally open' contact of each relay, with 12V (+) wired to the 'common' of each relay. The right two connectors are for the (+) and (-) 12V from a battery.

Tested it and thought I screwed something up, until I remembered I forgot to solder a jumper to configure it in Toggle mode. As shipped it's configured to momentary close the relay for one second (Momentary, or Mode 0) when the tones for the particular relay are received. For use in a logic circuit that might be desirable but for my intended use as more of a light switch I want it configured to toggle the relay and remain that way until I send the tones to toggle it the other way. Since I had already put the soldering iron away, and would need to change tips for soldering the tiny micro pads, decided to call it a day.

These have a lot of uses for home automation, like being able to call your BOL and turn on the furnace a couple hours before you arrive, I'm currently just using them with a Baofeng as the receiver for home security uses. Each relay requires a 7 digit control tone sequence to activate/deactivate it, if your sending/transmitting radio has DTMF autodial memories that's an easy way to program the tones for each so you don't need to memorize the tones for each one.

Edit to add the link to the controller: www.ebay.com/itm/282017607551 It shows some wiring configurations, but there are also two manuals for them you should be able to find by doing a web search on "AD22B04_4 channel DTMF controller commands setting manual".
 

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Discussion Starter · #9 ·
Using CTCSS codes in your radios also helps to add more security
Couldn't hurt imo.

Speaking of tones, as I was playing with the LCD display one it crossed my mind how voice inversion, enabled on both the sending and receiving radios, might make a DTMF encoded message a little more secure too.

Background: Not long after changing to our current VHF radios for group comms (our third attempt to get reliable short range comms for our group) around 2010, I selected ones with built-in voice inversion scramblers. We don't use it normally, but I wanted that option, mostly because I couldnt afford anything better/stronger. To see just how easy it was to defeat I recorded our scrambled communcations using a scanner and digital voice recorder, and moved the mp3 file to my computer to use de-inversion software on it. The software doesn't automatically deinvert it, but by playing with the inversion frequency settings in the program while listening to the recording it doesn't take long until you get close enough to the inversion freq that the words become intelligible. It may sound Donald Duck'ish, but it doesn't require finding the exact frequency to understand what is being said - "close enough" works. But DTMF tones are actually two tones (frequencies) combined to represent one of the 16 possible characters. 941 Hz and 1209 Hz tones combined being a " * " for example. So while it's a pretty wide window when deinverting speech to something understandable it may not be quite as wide a window when it comes to decoding inverted DTMF tones, it'll still need to be close enough that whatever they're using for a DTMF decoder (after deinversion/descrambling) can recognize it and decode it to the actual DTMF characters that were sent. Mostly just thinking out loud, but at least it would add an additional step that would further slow down anyone's decryption/decoding efforts.
 

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Discussion Starter · #10 ·
MURS Dakota Alert, with the main cover open and the PIR sensor cover removed to show the wiring.



The cube shaped item at the bottom is a standard 30 amp 12V automotive relay, and wired to the Dakota Alert such that when the motion sensor detects motion and transmits the "Alert Zone x" message the relay also closes while the message is being sent. Nothing is attached to the switch contacts of the relay of this spare detector, but I add one of these relays to each Dakota Alert to save time if I want to use it later. It fits nicely inside the plastic clips which seem to have been intended to hold a single 9V battery to power the Dakota Alert before the manufacturer switched to the 6 AA battery power pack. Currently of the four I have deployed around the offgrid homestead I'm only using the relay on two, both used inside outbuildings as intrusion monitors, and the relay switch contacts are connected to a car horn which sounds when motion inside is detected. In a ROL world I like this setup, as it alerts us about a 1/4 mile away by MURS radio that there's motion inside our buildings, but also the horn(s) sounding at the outbuildings will likely scare off the burglars. This may not be as effective in the city or 'burbs, where sirens and car horns are common 24x7, but in our remote offgrid area with no street lights or traffic and where you can hear a twig snap 100 yds away it's a little different. In a WROL situation I'll likely disconnect the horn so it's back to being a silent alarm by MURS radio only, because reasons.

A car horn being just one example of what could be activated by the relay when motion is detected obviously.
 

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you can also wire in series a second enclosure with PIR in series to give more coverage, in parallel to add false trigger redundancy or use a ELK security module to wire in a normally open contact closure for a door or window into the NC terminals on the board. This would give you the ability to hardwire in doors or windows into the same MURS transmitter
 
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