Project to detect open collector/ high impedance signals

1. Aug 17, 2006

dforde

I am trying to come up with a way to monitor a device that alarms. The signal is open collector: high impedance when not alarm. I would also like to be able to connect this to a computer and monitor and log the alarms when they happen. Any help would be greatly appreciated.

2. Aug 17, 2006

chroot

Staff Emeritus
Use a pull-up resistor. You can connect a TTL-level signal through your computer's parallel port. (This is the easiest way, at least.)

- Warren

3. Aug 17, 2006

dforde

Thanks for the reply, do you know of an available circuit design for this, and the pin assignments for the port, also what kind of software could I use for the monitoring of the alarms, any and all help is greatly appreciated, the commercial solution to this is very .

4. Aug 17, 2006

Staff: Mentor

I understand the desire to save money, but aren't there regulations governing alarm systems? In my experience, there are certain things that need to be done in a certain way, in order for a commercial building's insurance underwriter to approve of an alarm system.

5. Aug 17, 2006

dforde

This project is not for a building or anything like that, so there are no regulations involved, I have a number of alarm devices that when they alarm, there is a 3.5mm mono jack, tip is signal output, ring is 0V. Signal is open collector type: high impedance when not alarm, low. I want to be able to monitor the devices on a single computer, so I can log when they go off. Any help for a solution to this is appreciated, I am also trying to keep cost to a minimum. The pull-up resistor idea might work if I can get details on the setup, and appropriate software to monitor it.

6. Aug 17, 2006

chroot

Staff Emeritus
Schematics (and software) for interfacing TTL-level signals are all over the web -- try using google to search for them. Use a 5V pull-up resistor, and you should be fine.

- Warren