CDM External Alarm

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scvfd1204
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CDM External Alarm

Post by scvfd1204 »

Hello all,

I have looked all over the place on here, and can't really figure out how to do this.

Here is the setup I have right now.

I have a VHF CDM-1250 being used in a base station setup. What I am trying to do, is configure something that will ring a couple 120vac fire alarm bells when my station gets toned out. I currently have the radio set to beep once a call alert is received, and it keeps repeating and repeating until a key is pressed.

I would like to do this with as little purchasing as possible, since we are on a very limited budget (like most VFD nowadays). I have been told that I could use a relatively small PCB type relay connected to the accessory connector on the back of the radio, with a diode connected between the alarm output on the radio to ground. The person telling me about this isnt really familiar with the CDM series and their capabilities.

What I was thinking about was connecting a smaller 12vdc relay to the accessory connector in the radio, and using that to operate a larger relay with a 12vdc coil, and 120vac contacts. I would like for the relay contacts to close for about 1 to 2 seconds, so we wont miss any audio from the transmission.

I was thinking about doing this with an old Minitor II pager, but the only ones we have are for lowband, and we are now dispatched on highband. Currently, we are using Minitor IIIs and IVs, and there arent any extra ones.

Any input would be greatly appreciated, as the Chief keeps asking me about this, and I would like to really get everyones attention when we get toned out. The beeps just arent loud enough, and I want something that will "wake the dead" as one my my guys put it.

Thanks

Jeff
Surf City, NC
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wavetar
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Post by wavetar »

Pretty easy stuff. Pin 7 is ground, Pin 4 can be set for 'external alarm', you can choose between active high or low, and with the CDM series you can vary the time from 1-30 or more seconds, I believe. Other units such as Maxtrac & GM300 had a hard-set 6 second timer.

Todd
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Post by kmoose »

What make and model Fire Alarm? Do you want this to go to the panel as an alarm, or as a trouble? It might be better to run the beep you are using now, through a matching transformer, to a high output speaker.
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Post by nmfire10 »

I think he means just the bells from an old fire alarm system, not an actual connection to the alarm system. :wink:

There is also a delay timer for the external alarm. You can have it delay ringing the bells for up to 30 seconds I think and then you can make it latch the external alarm or set a duration as stated above.
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Post by kmoose »

Ah................I see that...............now. Is it still Monday? God, I hope not.
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scvfd1204
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Post by scvfd1204 »

Thanks guys. I was looking in the CPS at a codeplug from our CDM unit.

I saw that pin 4 could be set for external alarm, and the delays and external alarm time.

As far as amperage output on the pin 4 external alarm, what kind of limitations should I observe?

I do happen to have a relatively small Potter & Brumfield 12vdc coil relay with contacts rated for 120vac plus.

Is they any other type of hardware (diodes, resistors, etc) that should be placed anywhere in this configuration for it to work properly and not damage anything (other than circuit breakers, fuses etc)?

Thanks for your help so far!

Jeff
Surf City, NC
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wavetar
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Post by wavetar »

scvfd1204 wrote:Thanks guys. I was looking in the CPS at a codeplug from our CDM unit.

I saw that pin 4 could be set for external alarm, and the delays and external alarm time.

As far as amperage output on the pin 4 external alarm, what kind of limitations should I observe?

I do happen to have a relatively small Potter & Brumfield 12vdc coil relay with contacts rated for 120vac plus.

Is they any other type of hardware (diodes, resistors, etc) that should be placed anywhere in this configuration for it to work properly and not damage anything (other than circuit breakers, fuses etc)?

Thanks for your help so far!

Jeff
Surf City, NC
I do believe the output is limited to 250mA, the typical coil for a 12vdc relay draws virtually nothing, so it shouldn't be a concern.

Todd
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Post by HumHead »

A reverse EMF protection diode accross the relay coil is almost never a bad idea.
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scvfd1204
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Post by scvfd1204 »

Thanks for the further info.

I happened to find an old SSC siren decoder, and it happens to have that Potter & Brumfield K10P-11D15-12 relay in it. It is 12vdc coil, and the contacts are roated to over 120vac. I looked up the spec on this relay from the manufacturer, and the coil draws 75 milliamps. The relay has a diode across the coil leads. I figure it is safe to assume that the diode is in place to prevent feedback and whatnot.

Thanks for the help guys. I am going to try to get this project off the ground soon, and get things up and running.

Thanks again!

Jeff
Surf City, NC
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scvfd1204
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Post by scvfd1204 »

Another thing...

As far as connecting the 12vdc relay to the accessory connector on the back of the CDM, I should set pin 4 for external alarm, and connect the coil leads to pins 4 and 7, correct?

I am kinda confused (it has been a while since I have done anything near like this). In the CPS for the accessory configuration and accessory pin programming, what is the definition of ACTIVE HIGH and ACTIVE LOW?

I used to know all of this stuff, but it has been way too long since I have done anything like this.

Thanks again!

Jeff
Surf City, NC
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wavetar
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Post by wavetar »

I'm 99% sure active high puts out 12vdc for the pin 4 alarm output, as opposed to 5vdc. You can measure it for yourself before you hook it to your relay, if need be. Yes, you would hook it up exactly the way you described.

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jim
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Post by jim »

I always set up pin 4 as "0 VDC" active and keep the other side of the relay's coil to +12VDC through a 1A fast blow fuse. Use a 1N4007 across 85/86 to clamp the spike. 30/87 will control your AC device. You can always add a latching relay to drive a strobelight or such, if needed.

Make sure you set the external alarm to "permanent" arming and not maunual. Also, set up the signalling to "auto reset."

A Bosch relay peaks about 150 ma. on pullin and will sustain about 80-100 ma. while holding the relay closed.
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scvfd1204
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Post by scvfd1204 »

Ok, so from what I am gathering, I should set Pin 4 to "Actiove Level - Low", correct? Ok, so where do I get the +12vdc for the other side of the coil on the relay? From the power supply that is powering the radio?

I have the external alarm set to permanent arm, but the only setting for the auto reset is time in seconds. What should this be set to?

The way I am thinking about doing this is:

1 12vdc standard relay (75 milliamp coil current) with 120vac contacts. When the radio receives a page, the relays closes for 2 seconds. This is the relay that will ring the 120vac bells I have.

In addition to this, I have added a 12vdc latching relay (100 milliamp coil current), so once the first relay energizes, it will latch, and a 120vac strobe light in the bay will flash until it is reset by a pushbutton near the radio. I am going to use the second set of contacts on the first 12vdc relay to operate the coil on this relay, and then utilize a momentary pushbutton to reset it.

OK on the 1N4007 diode across the coil leads on the relay. One relay has the diode in place already, and I am going to add a diode to the second one.

The relays I have are rather low current. The only one that will connected to the radio output is a P&B relay, and the coil current for it is listed as 75 milliamps. It is a DPDT relay, so I can have one side swtiching 12vdc for the latching relay, and the other contacts will switch the alarm bells.

I would also like to connect a couple LEDs in this setup as well. Such as a power indicator, and a call indicator LED. All of the LEDs I have are listed as 2.0/2.2 typical voltage bi-color LEDs. How do I make these units operate from 12vdc? I remember something about adding a resistor in one lead of the LED, but I can't remember all of the specifics. It has been a long long time since I have learned this stuff, and my memory isn't what it used to be.

Thanks again guys! All of this input is helping me out more than you will ever know, and probbaly more than I will never know.

Thanks,

Jeff
Surf City, NC
jim wrote:I always set up pin 4 as "0 VDC" active and keep the other side of the relay's coil to +12VDC through a 1A fast blow fuse. Use a 1N4007 across 85/86 to clamp the spike. 30/87 will control your AC device. You can always add a latching relay to drive a strobelight or such, if needed.

Make sure you set the external alarm to "permanent" arming and not maunual. Also, set up the signalling to "auto reset."

A Bosch relay peaks about 150 ma. on pullin and will sustain about 80-100 ma. while holding the relay closed.
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scvfd1204
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Post by scvfd1204 »

OK Guys,

I have the radio programmed for permanent external alarm, with the correct timing setting (as far as I know).

The only thing I am trying to figure out now is this:

If I set Pin 4 to external alarm, Active HIGH, when the radio is powered off and then powered back on, 12 vdc is showing between pin 4 and ground. The only way to get this voltage to go away is to allow the radio to receive a call alert. After the appropriate external alarm time, the radio goes back to showing .6 volts between pin 4 and ground. If I set pin 4 for active LOW, it seems to work properly, by 12 vdc being present at all times, and when an alert is received, the voltage drops to .6.

Is the radio supposed to do this on the Active HIGH setting? If so, is there a different way to get the voltage between pins 4 and 7 to go away until an alert is received?

Thanks

Jeff
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Post by wavetar »

It shouldn't do what you're describing while active HIGH, but it's ringing a very fuzzy bell in my memory. What firmware version is the CDM1250? Seems to me that might have been an early bug...

Todd
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scvfd1204
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Post by scvfd1204 »

In the CPS it shows firmware as unknown, however it does show the codeplug version as 2.17, does that ring a bell?
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Post by wavetar »

The firmware will shown as 'unknown' if you're just reading the archived file. You need to read the radio directly to see the firmware version. How old is the radio?

Todd
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Post by scvfd1204 »

The radios were purchased in June of 2001. The original codeplug date is dated in April 2001.

Thanks again!!

Jeff
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jban
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Re: CDM External Alarm

Post by jban »

Found a bunch of CDM1250 in our surplus pile. Want to set them up for station alerting (that part is no problem). I am however, having the same problem on pin 4. It puts out 13.5vdc all the time. Firmware is R05.05.22. Radios shows June 2007. Is it a firmware issue? I would like to trip a relay and timer for alarm lights
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Re: CDM External Alarm

Post by jackhackett »

jban wrote:
Thu May 27, 2021 6:04 pm
Found a bunch of CDM1250 in our surplus pile. Want to set them up for station alerting (that part is no problem). I am however, having the same problem on pin 4. It puts out 13.5vdc all the time. Firmware is R05.05.22. Radios shows June 2007. Is it a firmware issue? I would like to trip a relay and timer for alarm lights
The first thing I'll say is, this thread can be a bit confusing.

The whole bit about active high/low is pretty much pointless. You would almost never want to set it for active high.
The comment from Jim is what you'd want.

The reason you want active low is because of the way the output circuit works. Pin 4 is tied to unswitched B+ (around 13.8V) through a 4700 ohm resistor, it then has a darlington transistor between it and ground.
Note that the voltage is unswitched, even with the radio off you will measure 13.8V on pin 4 (with no load on it).

For a high output the transistor is turned off, so if you measure the pin with a voltmeter you will see 13.8V (or thereabouts). But the resistor limits the current to around 3mA, not enough to drive a relay, if you connect one you'll only read around 1/4 volt across it, because it loads the output down. Active high mode is only meant to drive a very low current load.

For a low output the transistor is turned on, pulling the output down to around 0.6V. The transistor will allow much more current to flow, around 200mA, so it will drive a relay directly.

If you set it for active low, put a voltmeter on pin 4 and set off the alarm, you should see the voltage drop. If you don't, the transistor is probably fried.
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Re: CDM External Alarm

Post by jban »

Thanks. I did have set to low and one of them did drop to .06. The other stays at 13.5. Guess I will cull through them. Luckily I don't need this capability on all if them
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Re: CDM External Alarm

Post by jban »

I was hoping it would supply voltage upon activation
John B
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Re: CDM External Alarm

Post by jackhackett »

jban wrote:
Thu May 27, 2021 7:37 pm
I was hoping it would supply voltage upon activation
If you're going to drive a relay with it it really doesn't matter, you just connect the other side of the coil to the correct polarity.
Actually it's easier to wire a relay to a switched low output, it uses one less wire.

Say you have a Bosch relay to switch +13.8V, to drive it switched low you would use:
+13.8V to pin 30 and jumped from 30 to pin 86
Switched low output to pin 85
Load to pin 87

If they had made it so it could handle a relay load with the output switched high you'd have:
+13.8V to pin 30
Switched high output to pin 86
Load to pin 87
Ground to pin 85

So instead of a running a ground wire you end up with a little jumper between 30 and 86.
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Re: CDM External Alarm

Post by jban »

So doing this I have pin 4 with 13.5vdc normally and upon alert it reverts to .06 momentarily and that will trip the relay?
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Re: CDM External Alarm

Post by jackhackett »

Yes.
I notice you said you are going to use it to trip a timer. Do you know what model timer it is?
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