The Rentron page

http://www.rentron.com/3-bit-infrared.htm

shows some of the principles that you should try to
observe for good reliable IR comms

Short pulses allow greater instantaneous power through the
LEDs, but doesn't over-stress them with high average current.
You'll feel them getting warm if you start over-doing it. A large
reservoir capacitor (>100uF) right next to the LEDs will help
deliver this instantaneous current. You can isolate this cap
with a diode if necessary to prevent noise getting to the circuit

Depending on the voltage available, series or parallel LEDs
are a good idea. Choice of beam angle is up to you but the
narrower the LED's beam angle (eg 5-10 degrees rather than
60-80 degrees) means better line-of-sight efficiency. Narrower
beams tend to bounce off walls better

A carrier frequency, typically 40kHz. With that in mind, the
period of the pulses must be long enough to contain some
40kHz waves for the receiver to latch on to

Use a receiver that has an integral 40kHz filter. This improves
data extraction markedly, and outputs it as at logic levels as
well as giving good immunity from ambient light such as lights
or the sun. The Tiny IR would appear to use a carrier. Assuming
the Tiny IR is a PIC, you've 26 instruction cycles for a full carrier
wave (approx 4,000,000 / 4 / 38,000). Most convenient for a
system that has many command sequences is to store them in
a table and pull the bits out one at a time.

You'll have to decide on a protocol too. The presence of a
carrier indicates a "1"  bit,  but it doesn't tell you the context
of that "1". No carrier can either indicate a "0" or end-of-
transmission

Use a low-saturation high-speed transistor. The Zetex range
are ideal. Normal types (BC337, BC548 etc) may be fast
enough, but they do not have the switching speeds at high
current that the Zetex ones do

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body