Re: [Repeater-Builder] active low COR
At 6/3/2010 07:16, you wrote: >Hi Scott, > >Many controllers have pullup resistors on their COR inputs so that they >can be driven from open collector or relay contact COR outputs. With that >arrangement, if the controller is configured for active high and the COR >line is disconnected, the controller will think the receiver is active. > >The best arrangement is the one that works for you. There aren't any >standards -- except perhaps in industrial control, where there are fewer >active low circuits due to the possibility of activating a circuit due to >a pinched wire. I use active high on the COS & active low on the CTCSS. That way any failure that occurs equally to both lines will not key the TX. Bob NO6B
Re: [Repeater-Builder] active low COR
Scott, A while back there was a thread on this subject and one of the members posted the reply below. It really made a lot of sense and I saved it in my archives for future reference. Don, KD9PT Lastly, if you can do it, run your logic level signals as active low, for two reasons: 1) they are much easier to debug, 2) a blown fuse doesn't create a false signal. In addition I prefer to run the interfacing between radio and the controller as open collector since most controllers have their own internal pull-up resistors, and a open collector output is therefore universal - it will work with a five volt logic system, a +12 volt logic system, a relay, a LED (for testing), or anything else, and all with no modifications. Active low signals are easy to debug, and easy to interface - with proper design and component selection you can treat them as if they were a relay contact that goes to ground when active. With an active low environment when the signal is inactive, the transistor is switched off, the collector floats and is dragged high by the pullup resistor. When the signal is active the open collector is pulled to ground. As mentioned above, if you leave the input open (for example unplugging the cable between the control receiver and the controller) the pull-up resistor causes the input to go high. If you program the input for active low and unplug the cable it doesn't care. Personally, because of the above reasons, I dislike active high. I recommend that first you program your repeater controller COR, PL and logic inputs to be active low, and add a transistor inverter to your hardware if necessary. Another benefit of active low interfacing is if a radio loses power or otherwise fails, the pull-up resistor in the controller doesn't "pull up" the dead signal to a false active, resulting in the system being keyed until the timeout timer disables the system transmitter (you DO have a separate backup timeout timer, don't you?), thereby rendering the entire system unusable. Also when you are working on the system you can do a large amount of testing with nothing more than a clip lead shorting the open collector outputs to ground without worrying that you're going to blow something up (picture a site visit some day... PL decode not working? ground the PL decode lead and see if the PL indicator on the controller front panel lights up. yes? the problem's gotta be in the decoder itself inside the receiver chassis!). Also with open collector interfacing you can shut off the system, disconnect or un-cable the bad radio/device/etc. and then turn the system power back on and everything else in the system still works because the pullup resistor in the unplugged open circuit looks like an idle signal... - Original Message - From: scott w To: Repeater-Builder@yahoogroups.com Sent: Thursday, June 03, 2010 3:55 AM Subject: [Repeater-Builder] active low COR Hello to group, What is the advantage of an active low COR. Most I have talked to say they have their controllers set that way, so I set mine that way,plus the Maxtrac I am using as a receiver default is active low. I simulated a power failure to the reciever and the line went low and the transmitter thought it was time to transmit. I also accidently pulled the cord from the controller off the back of the receiver and again a low status and the transmitter thought it was time to transmit. Im not seeing a benefit of a active low COR in those repects. Should I go to active high or since those things dont usually happen often leave it LOW.. Any advice or ideas appreciated.. 73s
Re: [Repeater-Builder] active low COR
Hi Scott, Many controllers have pullup resistors on their COR inputs so that they can be driven from open collector or relay contact COR outputs. With that arrangement, if the controller is configured for active high and the COR line is disconnected, the controller will think the receiver is active. The best arrangement is the one that works for you. There aren't any standards -- except perhaps in industrial control, where there are fewer active low circuits due to the possibility of activating a circuit due to a pinched wire. 73, Bob Bob Schmid, WA9FBO, Member S-COM, LLC PO Box 1546 LaPorte, CO 80535-1546 970-416-6505 phone 970-419-3222 fax www.scomcontrollers.com -Original Message- From: scott w To: Repeater-Builder@yahoogroups.com Sent: Thu, Jun 3, 2010 2:55 am Subject: [Repeater-Builder] active low COR Hello to group, What is the advantage of an active low COR. Most I have talked to say they have their controllers set that way, so I set mine that way,plus the Maxtrac I am using as a receiver default is active low. I simulated a power failure to the reciever and the line went low and the transmitter thought it was time to transmit. I also accidently pulled the cord from the controller off the back of the receiver and again a low status and the transmitter thought it was time to transmit. Im not seeing a benefit of a active low COR in those repects. Should I go to active high or since those things dont usually happen often leave it LOW.. Any advice or ideas appreciated.. 73s
Re: [Repeater-Builder] active low COR
I prefer active high for just the reason that you described. I usually fuse my equipment individually, so a blown fuse in the receiver can cause an active low to be sent to the controller, thereby keying the transmitter. If I do use active low, I put a pull-up resistor in the controller and test it see if it keeps the COR high on a receiver power failure. Joe On 6/3/2010 4:55 AM, scott w wrote: Hello to group, What is the advantage of an active low COR. Most I have talked to say they have their controllers set that way, so I set mine that way,plus the Maxtrac I am using as a receiver default is active low. I simulated a power failure to the reciever and the line went low and the transmitter thought it was time to transmit. I also accidently pulled the cord from the controller off the back of the receiver and again a low status and the transmitter thought it was time to transmit. Im not seeing a benefit of a active low COR in those repects. Should I go to active high or since those things dont usually happen often leave it LOW.. Any advice or ideas appreciated.. 73s
[Repeater-Builder] active low COR
Hello to group, What is the advantage of an active low COR. Most I have talked to say they have their controllers set that way, so I set mine that way,plus the Maxtrac I am using as a receiver default is active low. I simulated a power failure to the reciever and the line went low and the transmitter thought it was time to transmit. I also accidently pulled the cord from the controller off the back of the receiver and again a low status and the transmitter thought it was time to transmit. Im not seeing a benefit of a active low COR in those repects. Should I go to active high or since those things dont usually happen often leave it LOW.. Any advice or ideas appreciated.. 73s
