Open collector output revisited

A while back I blogged about open collector outputs and its basic operation.  I included some diagrams, in particular Figures 7 and 8, which show how to interface an open collector with a relay.  Which relays will it work with?  I was going to say all relays, but in digging around, I found that there could be a minimum requirement for it to work properly.

The GE8016 QuickBridge Receiver is a wireless receiver with open collectors ouputs. Take a look at Figure 1 below.

A relay is connected between the receiver and the alarm panel terminals.  As long as the Zone 1 wireless sensor is “secure,” the  panel “sees” the resistor across Zone 1 and Return. If the sensor goes into alarm, the receiver’s zone 1 is pulled to ground, thus energizing the relay. This effectively shorts out the resistor and the panel goes into its alarm mode.  The minimal requirement for a relay to work with the GE8016 is that the relay coil must be at least 300 ohms.

I checked out the relay board offered by HAI, the HA10A071. This is a 4-relay module, and there’s even an 8-relay module, HA19A001, which would be perfect for use with the 8-channel Quickbridge Receiver, or so I thought.  The coil resistance on both modules are OK at 315 Ohms, but the modules won’t work because they have a common gound.  On the HAI relay modules, one side of all the coils are tied to ground.  To energize the relay, one must apply 12 VDC to the positive side of the coil. When12 VDC is applied, the relay energizes and the on-board LED lights up red providing a visual indicator that the relay has changed states.   See Figure 2. Or for a better image, click here.

 Hmmm…one, however, could hook things up in reverse and apply 12 VDC to the green J1 wire instead of connecting it to the controller’s earth ground and connect the T1 through T4 relay module terminals to the zones 1 through 4 of the  Quickbridge  Receiver and it should work just fine.  This I tried, and it did work, but the LED indicators no longer lit up when the relay was energized. If you want the LEDs to light up, don’t use this relay module with the Quickbridge.

So which relay can be used with the Quickbridge?  Use the ELK912 compact relay.  Hooked up as shown in Figure 3, the relay will operate in the same manner as the circuit in Figure 1. The HAI controller sees the 1 Kohm resistor when the zone is secure, and a short when not secure. Click here to see a full-size image.

 

 

 

 

 

Hope you found the above useful.  Any questions? Drop me a line, and thanks for taking the time to browse our blog.