The first project I posted to Robot Room involved a 74HC00 NAND infrared oscillator. Nine months have passed and I'd learned a lot. The power usage of my original NAND oscillator can be reduced without any loss of drive or functionality
- Swap in a Toshiba 74HC00A NAND
- Switch the 10-kilohm pull-up resistor for 100 kilohms
- Eliminate a whole inverting buffer gate by switching the 2N2222 NPN transistor driver to a 2N2907 PNP transistor driver.
EVEN BETTER
I wrote this web page in March 2001. The circuit presented here is perfectly good for builder the 38 kHz emitter. However, because I get a lot of questions about infrared sensors and detectors, I decided to dedicate two chapters (11 and 12) of my second book, Intermediate Robot Building, to the subject. Therefore, if you'd like more information, including an improved schematic with receivers and detectors, pick up a copy of the book.
Usage
The oscillator will be used to generate a square wave at a desired frequency. The wave is fed into a transistor that drives an infrared LED on and off very rapidly. Because the emissions are infrared and very fast, neither is visible to the human eye. Inexpensive infrared receiver chips are available at 36 kHz, 38 kHz, and 40 kHz. The receivers are sensitive to oscillations several kilohertz to either side, although reception distance improves with a better signal to start with. If used for object detection, the signal needs to travel the distance to the object, bounce off the object, and then travel the distance back to the receiver. So, distance becomes a factor.Because infrared receivers amplify the signal to improve detection, electrical noise generated from the oscillator can leak into the receiver and trigger a false detection. This isn't a problem for VCRs or most consumer devices as they tend to contain either a transmitter (remote control) or a receiver (CD player), but not both. Therefore, robot transmitter and receiver circuits must be carefully designed and positioned apart to be useful. Robots that chase electrical ghosts, spin in place, or jerk sporadically are initially amusing, but eventually frustrating. The lower the power of the circuit, the more likely it will be lower in noise. Also, liberal use of decoupling capacitors and metal shielding helps a lot. Greater distance between the circuits makes an enormous difference.
The Popular 555
The 555 IC is an extremely popular timer. The low-power CMOS versions (TLC555, LMC555, and ICM7555) use less power than the older (555, NE555, LM555) versions and don't require a capacitor on the control pin. Although pin and functionally compatible, the component values differ between the low-power CMOS and older versions.
