Nuts & Volts - February 2004

Tech Forum

Figure 1

LMC6082 is a dual, I used the second op-amp in a low-pass filter so the average voltage can be measured. The capacitors should be film type for accurate results. The internal offset of the op-amp is less than 1 mV, so I assumed that was neglectable.

Russell Kincaid Milford, NH

[11037 - November 2003]

Does anyone know of a simple data logger I can use to record the time and date of each instance a switch is turned on and off and keep it in memory?

coin cell that can easily be popped out of its holder. Some, quite possibly yours, will have a three-cell battery which is soldered in place near the edge of the motherboard. If this is the case, then look for a small header with three pins and a shorting plug near the battery. Moving the shorting plug to the opposite set of pins will disconnect the battery from the CMOS backup memory. In all cases, be sure that the power to the computer is off, otherwise the backup memory will be powered from the main supply and disconnecting it will have no effect.

[110310 - November 2003]

I need a circuit that will track a changing voltage (+0.1 to +0.9 V) and allow me to use a potentiometer to create an offset of ± 0 to 3 millivolts and adjust to an average of 0.45 V. This circuit is to track the output of an automotive O2 sensor.

The H06-001-02 Hobo™ Data Loggers from Onset will record up to 2,000 different changes (on/off) and the time each happens. They require the BoxCar 3. 7 (BC3.7-DL) software to download the information. This system was very user-friendly for me. Both should be at www.digikey. com

Brian German via Internet

David Sarraf Elizabethtown, PA

In this circuit (Figure 1), the LM78L05 provides isolation from the noise on the 12 V supply. The U1A amplifier circuit has unity gain for the input signal and the ± 5 volts that is available at the pot. You should use 1% resistors for accurate results. The MAX1681 is a + 5 to - 5 inverter; use film or ceramic 1 mF caps. Since the

[12031 - December 2003]

What is the difference between an S-video input and the plain old video input on a television set?

F o r

E l e c t r o n i c s

NUTS & VOLTS E v e r y t h i n g

An S-video cable is a higher grade of the plain old composite video input. The difference between the two is that S-video provides more bandwidth to the TV set. There are basicially two feeds coming in at once, chrominance and luminance (or color and brightness) and that's why there are four pins.

When using S-video, there is better picture quality. To put it in easiest terms, a data path for color and a path for brightness — where composite video has to accomodate for both and the picture sometimes looks "washed out".