September 2008 Tech Talk Online Q & A
Q: I have been heard that one should be careful at replacing standard Alkaline 9 volt batteries in smoke detectors with 9-volt Lithium batteries. To me it would seem that the Lithium battery would last a longer time so what is the problem?
A: Yes, you typically do get longer time with a Lithium battery. The caution is that a Lithium battery discharges at a different rate as an Alkaline battery and my not work with the typical 30 day low battery warning circuit of the smoke detector. While Alkaline batteries have a long, slow low battery decay, Lithium batteries keep a high voltage longer but drop more quickly near the end of the batteries life. Customers should be made aware that if they get a smoke detector’s low battery warning with a Lithium battery they should change it right away. It is always recommend that you check with the smoke detector manufacturer to find their recommendations on Lithium batteries.
Q: Recently I was working with some access control equipment that required a serial RS-232 connection with a PC computer. There was some trouble with the serial communications and it was thought that the serial port of the computer was bad. Is there a quick an easy way to test just he serial port (COMM(X)) of a computer?
A:
An old trick for testing a computer’s communication port is the use of a simple improvised hardware device call a loop-back plug. The two key pins in a RS-232 connector pins three and two, which are for signal receive and transmit respectively. If you short out these pins you are basically sending a transmitted signal back into the comm port receive, thereby testing the port. This can be done simply with a paper clip on a female DB-9 or a spare motherboard jumper on a male DB-9. You will need to use something like Microsoft Hyper-Terminal program to send test data to the port. Hint: If you have Echo on you will see double letters in this test.
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