Control a Servo with an LMR?

[Wags_Yokota]

Hello! First time user of this forum but I'm hoping you can help me out.

I'm stationed at an Air Base in Japan we have a need to control a small servo or actuator with a Motorola LMR or any other radio system? Does anyone know of any way, preferable a ready-to-use commercial solution, that connects to an LMR and uses the radio to control a small motor? Alternately, is there any way to activate a remote siren with an LMR?

Many thanks for any help!

 

[cpg178]

Many Motorola radios have pins on the back that can trigger relays when activated with various forms of signaling such as MDC, Two Tone, and with the newer radios DMR and P25 alerting. That relay could then activate your servo or siren.
Are you trying to do this over an analog or digital channel?

 

[Project25_MASTR]

Setting most commercial radios to perform some generic output action via their GPIO isn't trivial and as stated, can be done (especially with Motorola) in a various number of ways. Good if you are trying to do simple on/off commands but you are trying to analog or variable commands you will likely need to convert those values to serial data and send via some sort of modem/digital protocol (again, not trivial to do you just have to know how to do it).

 

[prcguy]

If the LMR has a discriminator output you could use an external CTCSS decoder and use a high tone like 250.3 Hz for fast response. In this case you can have a line go high or low for the duration of a transmission. You could even use two or more CTCSS decoders and program different channels with the same frequency but different tones to run the motor backwards, etc.

 

[RFI-EMI-GUY]

The old school way was to use DTMF for on/off or momentary relay closures. Below is a cheap solution. There are better decoders with some level of security, however even with a security code, the DTMF tones can be recorded and read by anyone and spoofed. DTMF is for analog FM radios. If your system is P25 or DMR the transmission and reception of the tones will be distorted. it would help to have some context of your application because a more sophisticated protocal may be required. There are SCADA products that use a digital signal and have more features, perhaps better for siren control.

https://www.amazon.com/Hilitand-AD22A08-Signal-Decoder-Controller/dp/B07CSZB976/ref=sr_1_10?keywords=dtmf+decoder&qid=1692035515&sr=8-10

 

[Wags_Yokota]

Everyone - thank you for your help!

So, the use-case is as follows. Yokota Air Base had a lightning strike that blew out an electric line that controlled an on-demand-only stoplight. The stoplight is not on a timer, it is only activated when needed similar to stopping traffic in front of a fire station. The stoplights are all powered and work fine, only the control line is damaged. It's probably damaged under the flightline and will take a long time to diagnose and repair. The stoplight operator is between 500 and 1,400 meters from the lights and the workaround is to have teams go out and manually flip a switch… which is a huge pain, waste time, and frustrating.

All we need is to flip a light switch with a radio, cellphone, or other wireless solution over a 1,400 meter distance. We have power on the lights we can draw from to power the controller. It does not need to be encrypted but that would be nice. We have a small team of Airmen to work on this problem but we need to know what to buy and how to configure it.

If anyone can give me an amazon parts list for what we need to buy and some instructions for how to configure the system, many Air Force Airmen would be extremely grateful! We have several Motorola APX 6000 radios and old cellphones for this use but could also buy a radio if needed.

 

[wa8pyr]

Everyone - thank you for your help!

So, the use-case is as follows. Yokota Air Base had a lightning strike that blew out an electric line that controlled an on-demand-only stoplight. The stoplight is not on a timer, it is only activated when needed similar to stopping traffic in front of a fire station. The stoplights are all powered and work fine, only the control line is damaged. It's probably damaged under the flightline and will take a long time to diagnose and repair. The stoplight operator is between 500 and 1,400 meters from the lights and the workaround is to have teams go out and manually flip a switch… which is a huge pain, waste time, and frustrating.

All we need is to flip a light switch with a radio, cellphone, or other wireless solution over a 1,400 meter distance. We have power on the lights we can draw from to power the controller. It does not need to be encrypted but that would be nice. We have a small team of Airmen to work on this problem but we need to know what to buy and how to configure it.

If anyone can give me an amazon parts list for what we need to buy and some instructions for how to configure the system, many Air Force Airmen would be extremely grateful! We have several Motorola APX 6000 radios and old cellphones for this use but could also buy a radio if needed.

Presumably all you need is a momentary button push, which starts the traffic light into a normal cycle, correct?

You could do this with Call Alert (or even QC2 or DTMF) and the Horn/Lights feature of a mobile radio, which uses a relay connected to the Horn/Lights pins on the accessory connector. When the proper call is received (CA, QC2, DTMF, etc), the relay is energized and makes or breaks the necessary contact. The reset delay can be programmed in the radio; once that delay time expires, the relay is de-energized and goes back to normal.

I've used this with Call Alert for fire station alerting many times, by simply using the relay to pass audio to the PA system in the firehouse (center pins of a DPDT relay to the radio speaker connector, NC contacts to a power resistor of approximately the same resistance as the impedance of the speaker - 8 ohm, 3.2 ohm, whatever - and NO contact to the proper input on the PA system. Works like a charm, and about all you need is the appropriate connector for the back of the radio, a diode and a SPDT or DPDT relay.

The instructions are in the back of the radio installation manual for XTL and APX mobiles.

If you're on a trunked system, I'd go with Call Alert.

 

[Firebuff880]

One of these offerings is probably a better choice than LMR radio is for this based on your latest update.

The uSwitch Product Line

The uSwitch is an ethernet web-controlled relay device that integrates with existing systems to keep your critical systems running. Contact us to learn more!

uhavecontrol.com

 

[xmo]

Wags_Yokota wrote: "It does not need to be encrypted but that would be nice."

If security is a concern, one solution might be to use the base trunking system if one is available. That would preclude any casual tinkerer from deducing the control method.

Otherwise, a simple decoder as suggested by RFI-EMI-GUY would be straightforward. The decoder would be connected to the receiving radio audio output and it can be configured for a latching function so the 'ON' command would enable the light which would stay on until the 'OFF' command is sent.

 

[KevinC]

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[AM909]

More than the parts needed, which you probably already have available, you need someone with some basic electronic skills to put it together in a way that won't fall apart during the first storm or when someone bumps into it.

APX could be used to send the necessary signal, but you'd need to have the software, hardware, and expertise needed to program it.

You'd then need a receiver with an output that can either drive a relay or connect directly to the switch. No need for an external decoder – most any mobile made in the last decades has some kind of selective call and a horn-relay or GPIO output that can be triggered by it.

[Add] Even some handheld radios may have such outputs, if form factor is an issue.

 

[RFI-EMI-GUY]

This device, RITRON Teleswitch packages the receiver (several bands available) and DTMF decoder into one package. It also responds with acknowledgment tone. You will need a DTMF analog FM transmitter to activate it. This could be a permanent solution.

https://prd-mp-docs.azureedge.net/ad417ac7-c753-43c0-a131-b1d4aad122e9/document/199e8dc8-8d14-4728-adc5-035cdac2d67c/teleswitch_ts142_442_10_08.pdf

Radio Controlled Remote Switch Teleswitch | Ritron Wireless Solutions

The TeleSwitch is a versatile, easy-to-use 2-way radio system to remotely turn off / turn on equipment as far away as 10 miles or more.

www.ritron.com

It appears this second device will send DTMF codes from a contact closure. You might want to ask a RITRON dealer to quote to your requirements.

https://prd-mp-docs.azureedge.net/ad417ac7-c753-43c0-a131-b1d4aad122e9/document/bc8fc303-824f-4bf1-8b49-2da7babb9966/quicktalksellsheetfeb2012.pdf